Science 3 is this the real life, Science 2 electric boogaloo
46.Driving along the road at 88 km/h, Reckless Rick runs into Hapless Harry, who is directly in front of him and is driving at 80 km/h. What is the impact speed—that is, the speed of the two vehicles the moment after collision?
0km/h
what happens when a fisher goes upstream with a 10m/s current boat gies at 27 mph compared to water. Compared to land
27m/s. 17m/s
44.A business jet of mass 30,000 kg takes off when the thrust for each of two engines is 30,000 N. Show that its acceleration is 2 m/s2.
2m/s/s=60000N/ 30000kg
43.The sketch shows a painter's scaffold in mechanical equilibrium. The person in the middle weighs 500 N, and the tension in each rope is 400 N. What is the weight of the scaffold?
300 N
48.(a) Show that the average speed of a tennis ball is 48 m/s when it travels the full length of the court, 24 m, in 0.5 s. (b) How would greater air resistance affect the travel time?
48m/s=24/0.5 Greater air resistance greater travel time
59.Rank, from greatest to least, the net force on the block in the four situations, A, B, C, and D.
C,A,B,D
58.The weights of Burl, Paul, and the scaffold produce tensions in the supporting ropes. Rank, from greatest to least, the tension in the left rope in the three situations, A, B, and C.
C,B,A
Equilibrium rule
EF=0
49.The heavyweight boxing champion of the world punches a sheet of paper in midair, bringing it from rest up to a speed of 25.0 m/s in 0.050 s. The mass of the paper is 0.003 kg. Show that the force of the punch on the paper is only 1.5 N.
F=ma=m×Δv/Δt=0.003 kg×25.0 m/s/0.050 s=1.5 N
free fall
Falling under the influence of gravity alone— falling without air resistance.
The action force and the reaction force that occur in an interaction.
Force pair
77.Why can a boxer hit a heavy opponent harder for the same punch than she or he can hit a light opponent?
Hitting involves an interaction between the hitter and the hit. A boxer cannot hit an opponent harder than the opponent can 'hit' back. The amount of hitting force is greater in the interaction between a boxer and a heavy opponent than with a lighter one, just as a punch delivers more force to a heavy bag than to a piece of tissue paper
75.Can an object be in mechanical equilibrium when only a single force acts on it? Defend your answer.
If only a single nonzero force acts on an object, its motion will change and will not be in mechanical equilibrium. There would have to be other forces to result in a zero net force for equilibrium.
When do action and reaction forces cancel each other
If these are the only horizontal forces, with no external force, no net acceleration of the system occurs.
Mutual action between objects during which each object exerts an equal and opposite force on the other.
Interaction
Two assertions of Aristotle held sway for some 2000 years.
One was that heavy objects necessarily fall faster than lighter objects. The other was that moving objects must necessarily have forces exerted on them to keep them moving.
So, overall, does ball A or ball B have the greater average speed? (Do you wish to change your answer to Exercise 107?)
Overall, the two will both exit at the same time because A will roll down a straight path with one boost. B will be rolling down with two boosts, but it will then reach an upward hill that will cancel out one of the boosts, so it will slow down long enough for the other one to catch up.
The speed at which the acceleration of a falling object terminates when air resistance balances its weight.
Terminal speed
Net Force
The combination of all forces that act on an object.
air resistance
The force of friction acting on an object due to its motion in air.
Support Force
The force that supports an object against gravity, often called the normal force.
60.The Moon travels in a nearly circular path around Earth. If somehow gravitation between Earth and Moon disappeared, how would the Moon's path differ?
The moon would gon away from the earth in a constant speed at a syraight line forever unless acted on by an outside force. This is because of NEwton's 1st law. Itb would be moving because it moves around the earth in a circle so it would be like a rockj in a a sling
Inertia
The property by which objects resist changes in motion.
hang time
The time that one's feet are off the ground during a vertical jump.
kilogram
The unit of mass. One kilogram (kg) is the mass of 1 liter (L) of water at 4°C.
Newtons 3rd law simplieifed
To every action there is always an opposed equal reaction.
Formulas for falling objects starting from a rest position
V=G*T
Formula for change in velocity
V=Vf-Vi
The symbol Σ stands for
Vector of the sum
104.Suppose that you're in a moving car and the engine stops running. You step on the brakes and slow the car to half speed. If you release your foot from the brakes, will the car spontaneously speed up a bit, or will it continue at half speed and slow due to friction? Defend your answer.
WHen you slow down your inertia jerks you forward from still beng in the preivious motion of being fast and when you release the brales it jerks you back from being in the previous motion of slow. You are not speeding up, you will, however slow down due to friction.
Objects don't speed up, slow down, or change direction unless
a force acts
Only when there is no force at all, or when two or more forces combine to zero, can an object
be in equilibrium
You cannot change speed without
changing velocity
3 types of friction
fluid, sliding, rolling
Is the speed gained by ball B going down the extra dip the same as the speed it loses going up near the right
hand end and doesn't this mean that the speeds of balls A and B will be the same at the ends of both tracks?- Yes it will because both dips are the same height which means they will have the same downward and upward force. B is also losing speed from gravity when going up the hill so it will return to the speed of only one boost just like A. In conclusion, yes they will both be exiting at the same speed.
44.A different scaffold that weighs 400 N supports two painters, one weighing 500 N and the other weighing 400 N. The reading in the left
hand scale is 800 N. What is the reading in the right-hand scale?-500N
m stands for
meters
mass is
more fundamental than weight; it is a fundamental quantity that completely escapes the notice of most people.
hevaier
more speed harder to get going.
Galileo was concerned with how things
move rather than why they move
net force equiblibrium rule
must have 0 net force to be in equilibirum because the main forces acting on something cancel each other out
Most often, air resistance is not
negligible for falling objects.
Which exerts the force and which receives the force? Isaac Newton's answer to this was that
neither force has to be identified as "exerter" or "receiver," and he concluded that both objects must be treated equally.
hen we say "force," we imply the total force, or __________, acting on an object.
net force
velocity is inversely proportional to
surface area
terminal velocity
the point at whih the downard force of air resistance equal each other. Object will not accelrate (equilibirum). Max accleration in air or on road as fast as you can go.
When direction doesn't change, acceleration may be expressed as
the rate at which speed changes
newtons third law simplified
you cant touch without being touched
The greater weight is more effective in ______________ air, resulting in a higher terminal speed for a heavier person. Increasing ____________ area reduces terminal speed.
"plowing through"; frontal
47.An airplane with an airspeed of 90 km/h lands on a runway where the wind speed is 40 km/h. What is the landing speed of the plane if the wind is head on? What is its landing speed if the wind is a tailwind, coming from behind the airplane? What would be the landing speed of the 90km/h plane landing in a headwind of 90 km/h?
-A. 50km.h B. 130km.h C. 0km/h
55.A ball is thrown straight up with enough speed so that it is in the air for several seconds. What is the velocity of the ball when it reaches its highest point? What is its velocity 1 s before it reaches its highest point? What is the change in its velocity, Δv, during this 1s interval? What is its velocity 1 s after it reaches its highest point? What is the change in its velocity, Δv, during this 1-s interval? What is the change in its velocity, Δv, during the 2-s interval from 1 s before it reaches the highest point to 1 s after it reaches the highest point? (Caution: We are talking about velocity, not speed.) What is the acceleration of the ball during any of these time intervals and at the moment the ball has zero velocity?
-A. Velocity at the highest point is instantaneously zero. B. One second before reaching its highest point, its velocity is 10 m/s. C. The amount of change in velocity is 10 m/s downward during this 1-second interval (or any other 1-second interval). D. One second after reaching its highest point its velocity is 10 m/s downward. E. The change in velocity during this (or any) 1-second interval is 10 m/s downward. F. The change in velocity, from 10 m/s up to 10 m/s down, is 20 m/s downward (not zero). G. The acceleration of the ball is 10 m/s2 downward before reaching its highest point, when reaching the highest point, and after reaching the highest point. In all cases acceleration is downward, toward Earth.
52.A force F acts in the forward direction on a cart of mass m. A friction force f opposes this motion. Use Newton's second law and show that the acceleration of the cart is F−fm. Show that if the cart's mass is 4.0 kg, the applied force is 12.0 N, and the friction force is 6.0 N, the cart's acceleration is 1.5 m/s2.
1.5m/s/s=(12N-6N)/4kg
56.A school bus slows to a stop with an average acceleration of −2.0 m/s2. Show that it takes 5.0 s for the bus to slow from 10.0 m/s to a stop.
10m/s/2m/s/s=5s
96.Harry the painter swings year after year from his bosun's chair. His weight is 500 N, and the rope, unbeknownst to him, has a breaking point of 300 N. Why doesn't the rope break when he is supported as shown at the left? One day, Harry was painting near a flagpole, and for a change, he tied the free end of the rope to the flagpole instead of to his chair, as shown at the right. Discuss with your friends why Harry took his vacation early.
2 ropes being held= double strength. 1 rope being held= single strength.
73.Suppose the monkey weighs 100 N and the vine supporting her pulls upward with a force of 120 N. What is the net force on the monkey? Describe her motion.
20 N. her motion is that she is going upwards and something is pulling upwards on the vine. More than two forces are pulling upward. She will go upward until the force pulling her upward stops pulling or the force pulling her upwards is less than or equal to her own weight. The net force is 120 N − 100 N = 20 N, so the monkey accelerates upward while the force acts.
50.Suzie Skydiver with her parachute has a mass of 50 kg. Before opening her chute, what force of air resistance will she encounter when she reaches terminal velocity? What force of air resistance will she encounter when she reaches a lower terminal velocity after the chute is open? Discuss why your answers are the same or different.
5N, 5N, They are the same because when falling the downward force never changes. In this case, your mass never chanegs when falling
52.Extend Table 1.2 (which gives values from 0 to 5 s) from 6 s to 10 s, assuming no air resistance.
6s 60 m/s 140 m; 7s 70m/s 155m; 8s 80m/s 170 m; 9s 90m/s 185m; 10s 100m/s 200m
41.Lucy Lightfoot stands with one foot on one bathroom scale and her other foot on a second bathroom scale. Each scale reads 350 N. What is Lucy's weight?
700 N
98.When the strong man in Exercise 97 exerts a downward force of 900 N on the rope, how much upward force is exerted on the block?
900 Newtons because the man is pulling on the rope that holds the block so on his side, he is exerting a downward force of 900 N, but on the other side, he is causing an upward force of 900 N to lift the block. He may not leift it, but he still exerting a force on it.
59.The strong man is pulled in the three situations shown. Rank, from least to greatest, the amount of tension in the rope in his right hand (the one attached to the tree in B and C).
A = B, C
vector quantity
A quantity whose description requires both magnitude and direction.
45.A horizontal force of 120 N is required to push a bookcase across a floor at a constant velocity. What is the net force acting on the bookcase How much is the friction force that acts on the sliding bookcase? How much friction force acts on the bookcase when it is at rest on a horizontal surface without being pushed?
A. 0N B. 120N C. 0N
54.A ball is thrown straight up with an initial speed of 30 m/s. How much time does it take for the ball to reach the top of its trajectory? Show that it will reach a height of 45 m (neglecting air resistance).
A. 2s B.30=45m/1.5s
49.(a) Show that Leslie's average speed is 10 km/h when she runs to the store 5 km away in 30 min. (b) How fast is this in units of m/s?
A. 5km/h/0.5h=10km/h B. 10km divided by h* 1h/3600s*1000m/1km=2.8m/s
50.(a) Show that the acceleration is 7.5 m/s2 for a ball that starts from rest, rolls down a ramp, and gains a speed of 30 m/s in 4 s. (b) Would its acceleration be greater or less if the ramp were a bit less steep?
A. 7.5m/s/s=30m/s/4s B. less
60.Different materials, A, B, C, and D, rest on a table. (a) Rank the materials, from greatest to least, by how much they resist being set into motion. (b) Rank the materials, from greatest to least, by how much support force (normal force) the table exerts on them.
A. B,A,C,D B. B,A,C,D
57.An airplane starting from rest at one end of a runway accelerates uniformly at 4.0 m/s2 for 15 s before takeoff. What is its takeoff speed? Show that the plane travels along the runway a distance of 450 m before takeoff.
A. From v = v0 + at, and with v0 being zero, v = at = (4.0 m/s2)(15 s) = 60 m/s. B. With v0 being 0, d = ½at2 = ½(4 m/s2) (15 s)2 = 450 m.
69.You hold an apple over your head. (a) Identify all the forces acting on the apple and their reaction forces. (b) When you drop the apple, identify all the forces acting on it as it falls, as well as the corresponding reaction forces.
A. Two force pairs act; Earth's pull on the apple (action), and the apple's pull on Earth (reaction). Hand pushes apple upward (action), and apple pushes hand downward (reaction). B. If air resistance can be neglected, one force pair acts; Earth's pull on apple, and apple's pull on Earth. If air resistance counts, then air pushes upward on apple (action) and apple pushes downward on air (reaction).
47.Leroy, who has a mass of 100 kg, is skateboarding at 9.0 m/s when he smacks into a brick wall and comes to a dead stop in 0.2 s. Show that his deceleration is 45 m/s2. Show that the force of impact is 4500 N. (Ouch!)
A. a=ΔvΔt=9.0 m/s/0.2 s=45 m/s2 B. F=ma=(100 kg)(45 m/s2)=4500 N
58.Three parachutists, A, B, and C, have reached terminal velocity at the same altitude. (a) Rank their terminal velocities from fastest to slowest. (b) Rank the order of their reaching the ground from longest time to shortest time.
A. c,a,b B. c,a,b
51.Lillian rides her bicycle along a straight road at an average velocity v. Write an equation showing the distance she travels in time t. If Lillian's average speed is 7.5 m/s for a time of 5.0 min, show that she travels a distance of 2250 m.
A. d=? From v=d/t d=vt B. First, we need a consistent set of units. Since speed is in m/s let's convert minutes to seconds: 5 min= 300s Then d=vt=(7.5m/s)(300s)=2250 m
103.In the absence of air resistance, a ballplayer tosses a ball straight up. (a) By how much does the speed of the ball decrease each second while it is ascending? (b) By how much does its speed increase each second while it is descending? (c) How does the time of ascent compare to the time of descent?
A. the ball slows by 10 m/s each second, and B. gains 10 m/s when descending. C. With no air resistance the time of ascent equals the time of descent.
53.A car races on a circular track of radius r. Write an equation for the car's average speed when it travels a complete lap in time t. The radius of the track is 400 m, and the time to complete a lap is 40 s. Show that the average speed around the track is about 63 m/s.
A. v=d/t=2(pi)r/t B. V=2(pi)r/t=2(pi)(400m)/40s=63m/s
formula for acceleration
A=change in velocity/ time interval
93.Consider a freely falling object dropped from rest. What is its acceleration at the end of 5 s? At the end of 10 s? Defend your answer (and distinguish between velocity and acceleration).
Acceleration is 10 m/s2 downward, constant, all the way down. (Velocity, however, is 50 m/s downward at 5 seconds, and 100 m/s downward at 10 seconds.)
89.What is the acceleration of a Tesla automobile that maintains a constant velocity of 150 km/h?
Acceleration is zero since there's no change in velocity.
There is a simple rule for identifying action and reaction force pairs. First, identify the interaction—one thing (object A) interacts with another (object B). Then, action and reaction forces can be stated in the following form:
Action: Object A exerts a force on object B. Reaction: Object B exerts a force on object A.
109.A couple of your friends say that before a falling body reaches terminal velocity, it gains speed while acceleration decreases. Do you agree or disagree with your friends? Defend your answer.
Agree with your friends. Although acceleration decreases, the body is nevertheless gaining speed. It will do so until it reaches terminal speed. Only then will it not continue gaining speed.
107.Can you think of a reason why the acceleration of the object thrown downward through the air in Exercise 106 would actually be less than 10 m/s2?
Air resistance on the thrown object decreases the net force on it (mg − R), making its acceleration less than that of free fall.
Vector
An arrow that represents the magnitude and direction of a quantity.
Europeans thought like
Aristotle
62.Knowledge can be gained by philosophical logic, and also by experimentation. Which of these did Aristotle favor, and which did Galileo favor?
Aristotle preferred to use philosophical logic in his search for knowledge. He would use common knowledge and reasoning to develop theories on how the world works. Galileo, on the other hand, preferred experimentation. He would use tests to provide solid evidence for his claims, which would make his assumptions more accurate than somebody who uses reasoning, which is not something that can be tested multiple times over to see if anything contradicts it. Nobody used experimentation till Galileo. Used experimentation to verify it.
Aristotle life
Aristotle was the foremost philosopher, scientist, and educator of his time. Born in Greece, he was the son of a physician who personally served the king of Macedonia. At age 17, he entered the Academy of Plato, where he worked and studied for 20 years until Plato's death. He then became the tutor of young Alexander the Great. Eight years later, he formed his own school. Aristotle's aim was to systematize existing knowledge, just as Euclid had systematized geometry. Aristotle made critical observations; collected specimens; and gathered, summarized, and classified almost all of the existing knowledge of the physical world. His systematic approach became the method from which Western science later arose. After his death, his voluminous notebooks were preserved in caves near his home and were later sold to the library at Alexandria. Scholarly activity ceased in most of Europe through the Dark Ages, and the works of Aristotle were forgotten and lost in the scholarship that continued in the Byzantine and Islamic empires. Several of his texts were reintroduced to Europe during the 11th and 12th centuries and were translated into Latin. The Church, the dominant political and cultural force in Western Europe, at first prohibited the works of Aristotle and then accepted and incorporated them into Christian doctrine.
64.A bowling ball rolling along a lane gradually slows as it rolls. How would Aristotle probably interpret this observation? How would Galileo interpret it?
Aristotle would reason that an object can only keep moving if a force acts on it. If not, it would return to it's natural rest. Galileo would determine that an object doesn't necessarily need a force acting on it to keep it moving. It's inertia would keep it moving forever, but an opposing force called friction would slowly start to slow it down until it reaches an equilibrium, or it's resting point. Aristotle would say the ball has a nutral resting place and for it to keep moving, a force had to keep it moving. Galileo would say inertia would keep it moving forever, but it would be stopped by rolling and fluid friction.
100.The opening photo in this chapter shows a favorite demonstration of author Steve Hewitt lying on his back with a blacksmith's anvil placed on his chest. When assistant Will Maynez whacks the anvil with a strong sledgehammer blow, Hewitt is not injured. How is the physics here similar to that illustrated in Figure 1.8 (the girl with a stack of books on her head)?
As a force travels through an object, the object's inertia makes the force smaller and smaller. This is true because Newton's 1st law states that all objects will remain in their state of motion unless acted upon by an outside force. This proves that if the force of the hammer beggins to go through the items or the anvil to reach the person and hurt them, the objects begin to resist the new outside force because of their inertia and break down the force as it travels until the force is either gone or so little that it doesn't hurt you
81.Suppose two carts, one twice as massive as the other, fly apart when the compressed spring that joins them is released. How fast does the heavier cart roll compared with the lighter cart?
As in the preceding exercise, the force on each cart will be the same. But since the masses are different, the accelerations will differ. The twice-as-massive cart will undergo only half the acceleration of the less massive cart and will gain only half the speed.
101.When a ball is tossed straight up, it momentarily comes to a stop at the top of its path. Is it in equilibrium during this brief moment? Why or why not?
At the top of its path (and everywhere else along its path) the force of gravity acts to change the ball's motion. Even though it momentarily stops at the top, the net force on the ball is not zero and it therefore is not in equilibrium.
Does ball B roll faster along the lower part of track B than ball A rolls along the straighter track A?
B rolls faster because it gains speed going more downhill. A, on the other hand, gains only one boost while B gains two. This will be canceled out however when it reaches thedip going up since it is the same as the dip going down, but instead of boosting, it is slowing down.
74.You tell your friend that the acceleration of a skydiver decreases as falling progresses. What is your response when your friend asks if this means the skydiver is slowing down?
Because acceleration is decreasing doesn't mean an object is slowing down. If an object is moving at 10m/s/s and after the 1st second it is moving at 10m/s. Then, let's say the acceleration will change to 9m/s/s after the 1st second as well. Once the second second arrives, the object will be moving at 19m/s because it is still gaining momentum, but at a lower rate. Eventually the object will reach terminal velocity where the acceleration will be 0, but it will still be moving because it has gained all that speed from before the acceleration hit 0, but it is no longer gaining any new speed
64.Aristotle claimed that the speed of a falling object depends on its weight. We now know that all objects in free fall, whatever their weight, undergo the same rate of change in speed. Why does weight not affect acceleration?
Because of air resistance, if there is more weight on an object, it will accelerate, but as it accelerates, inertia or air resistance (depending on what is happening) will act on the object. The more weight that acts on an object, the more inertia/ air resistance, which means it will balance out any amount of weight. If one weighed 10 lbs and had 2m/s, it would fall at 10 m/s^2 because that is what gravity exerts on anything. If another object fell at 20 lbs and had 4 m/s it would just be like the first one, and if you divided these two equations, you would get the same answer. Basically NEwton's second law in equation form is net force dividedf by mass is accelration. In this case the net force is weight.
66.When a ball rolls down an incline, it gains speed because of gravity. When a ball rolls up an incline, it loses speed because of gravity. Why doesn't gravity play a role when it rolls on a horizontal surface?
Because the ball is at rest and gravity presses it down, which would cause it to move if it were on a slope. Since it is not, however, gravity is just pushing it down, not sideways. An outside force is acting on the object to move it. Gravity is simply just pushing down, while an outside force can push anywhere depending on what the force is. Support fprce acts on an object from the dirction the ground is. If it wall on level grounf, it would point up. If it was on slanted ground it would point in the direction the ground is facimg. Vector result. Even the slightest change can affect this.
73.How does the weight of a falling body compare with the air resistance it encounters just before it reaches terminal velocity? Just after it reaches terminal velocity?
Before reaching terminal velocity, weight is greater than air resistance. After reaching terminal velocity both weight and air resistance are of the same magnitude. Then the net force and acceleration are both zero.
One of the arguments against a moving Earth was the following:
Consider a bird sitting at rest on a branch of a tall tree. On the ground below is a fat, juicy worm. The bird sees the worm and drops vertically below and catches it. It was argued that this would be impossible if Earth were moving. A moving Earth would have to travel at an enormous speed to circle the Sun in one year. While the bird would be in the air descending from its branch to the ground below, the worm would be swept far away along with the moving Earth. It seemed that catching a worm on a moving Earth would be an impossible task. The fact that birds do catch worms from tree branches seemed to be clear evidence that Earth must be at rest.
81.In order to slide a heavy cabinet across the floor at constant speed, once it is sliding you exert a horizontal force of 550 N. Is the force of friction between the cabinet and the floor greater than, less than, or equal to 550 N? What happens to the cabinet if your push exceeds 550 N? Defend your answer.
Constant speed implies the net force on the cabinet is zero. So friction is 550 N in the opposite direction. If you push harder, the carton speeds up because your force is greater than the force of friction.
91.Correct your friend who says, "Japan's bullet trains can easily round a curve at a constant velocity of 160 km/h."
Constant velocity means constant direction, so your friend should say "... at a constant speed of 160 km/h."
Formula for force of gravity directly and inversely proprotional
D: Mass I: D^2
formula for hang time
D=1/2*G*T^2
In the final days of his life, at the urging of close friends, Copernicus sent his manuscript, _______________,** to the printer.
De Revolutionibus Orbium Coelestium
Speed
Distance traveled per unit time.
102.Suppose that a freely falling object falls from a rest position and is equipped with an odometer. What equation is most appropriate for determining the distance fallen each second?
Do the readings indicate equal or unequal distances of fall for successive seconds? Explain. D=1/2*G*T^2 (formula for free fall) because the object is falling and we are trying to find the distance fallen each second. We would plug in 1 for T and plug in the other numbers and that would give us our answer.
77.Nellie Newton hangs at rest from the ends of the rope as shown. How does the reading on the scale compare with her weight?
Each scale shows half her weight.
87.Emily Easygo can paddle a canoe in still water at 8 km/h. How successful will she be at canoeing upstream in a river that flows at 8 km/h?
Emily will not be successful, for her speed will be zero relative to the land.
45.A rocket of mass 100,000 kg undergoes an acceleration of 2 m/s2. Show that the net force acting on it is 200,000 N.
Fnet=ma=(100,000 kg)(2 m/s2)=200,000 N
formula for force
Force=Mass*Acceleration
Motion under the influence of gravitational pull only.
Free fall
83.In Figure 1.15 we see Marie pushing horizontally on a table that slides across the floor at constant velocity. If she pushed with the same amount of force, but directed that force downward a bit, how would the amount of friction of the table legs with the floor be affected? Defend your answer.
Friction would be greater. With a somewhat downward push, the table would press harder against the floor (as if it were heavier). More friction acts on a sliding heavy table than on a lighter one.
Galileo life
Galileo was born in Pisa, Italy, in the same year Shakespeare was born and Michelangelo died. He studied medicine at the University of Pisa and then changed to mathematics. He developed an early interest in motion and was soon at odds with others around him, who held to Aristotelian ideas on falling bodies. He left Pisa to teach at the University of Padua and became an advocate of the new theory of the solar system advanced by the Polish astronomer Copernicus. Galileo was one of the first to build a telescope, and the first to direct it to the nighttime sky and discover mountains on the Moon and the moons of Jupiter. Because he published his findings in Italian instead of in Latin, which was expected of so reputable a scholar, and because of the recent invention of the printing press, his ideas reached many people. He soon ran afoul of the Church and was warned not to teach and not to hold to Copernican views. He restrained himself publicly for nearly 15 years. Then he defiantly published his observations and conclusions, which were counter to Church doctrine. The outcome was a trial in which he was found guilty, and he was forced to renounce his discoveries. By then an old man broken in health and spirit, he was sentenced to perpetual house arrest. Nevertheless, he completed his studies on motion, and his writings were smuggled out of Italy and published in Holland. His eyes had been damaged earlier by viewing the Sun through a telescope, which led to blindness at age 74. He died four years later.
90.The photo shows Steve Hewitt and his daughter Gretchen. Is Gretchen touching her dad, or is he touching her? Explain.
He is touching her and she is touching him. This is true because Newton's 3rd law states that for every action, there is an equal and opposite reaction. If Steve is touching his daughter as an action, then the reaction is that his daughter is touching him as well, or if his daughter is touching him, his reaction is that he is touching his daughter. If that doesn't prove it then this will: they are both literally touching each other with their hands. Steve has grabbed his daughters arms and his daughter has grabbed his arms. They are both sending actions to each other and receiving reactions from each other.
92.The auto in the sketch moves forward as the brakes are applied. A bystander says that during the braking interval, the auto's velocity and acceleration are in opposite directions. Do you agree or disagree?
I agree because when you step on the breaks, you decelerate the vehicle. You make the acccelration go into the negatives and it slows the car down to a stop, or it goes to an opposite direction and acclerates from there which decreases the speed going the other way
117.The bricks in this road were originally straight. Describe evidence for tires pushing the bricks in the wavy pattern, and explain why they do so.
If the tires didn't push on the road the bricks would still be straight. Where the bricks fold toward the left, tires have pushed in that direction. Where the bricks fold to the right, tires have pushed in that direction. Tires push when the car accelerates forward, gaining speed, and in the opposite direction when tires push backward as the cars brake.
85.What is the impact speed when a car moving at 100 km/h collides with the rear of another car traveling in the same direction at 98 km/h? What is the impact speed when they collide head on?
Impact speed is 100 km/h − 98 km/h = 2 km/h, a small bump. Head on is 100 km/h + 98 km/h = 198 km/h, lethal!
82.Consider your desk at rest on your bedroom floor. As you and your friend start to lift it, does the support force on the desk provided by the floor increase, decrease, or remain unchanged? What happens to the support force on the feet of you and your friend?
It becomes less because you are helping the support force, so it decreases it's power because it only exists to equal out gravity and as you lift the desk it slowly turns to 0 when it is lifted because yu have equalled the support force and surpassed it, causing you to lift the table.
78.A hockey puck at rest is in equilibrium. Is it in equilibrium if it slides across ice at constant velocity? Defend your answer.
It is because an object is the vector sum of forces acting on an object (in this case, friction and an outside force) and is not accelerating equals zero. A constant speed is a speed that doesn't change or accelerate, so that means the vector sum is zero. When a vector sum equals zero, that means it is in equilibrium, so in this case it is in a type of equilibrium called dynamic equilibrium in which an object that is in a constant speed is in equilibrium.
On track B, won't the average speed dipping down and up be greater than the average speed of ball A during the same time?
It will be dipping down, but dipping backup will make the average speed of B the same as A. This is because since they are both the same height, B will lose as much as it gained, so the boost and deboost will cancel each other out.
84.When the athlete holds the barbell overhead, the reaction force is the weight of the barbell on his hand. How is this force different when the barbell is lifted at an increasing speed?
It will only occur whe he begins to lift it and when he begins to slow down when he gets close to finishing lifting it in the air. WHen he begins or ends the weight's inertia will kick in and reists the change of motion. Atthe beginning it will exert mroe force to stop from being lifted or changed in it's form of mpotion andit will exert force to resist it being stopped or its motion being chaneghd again becaus eof NEwton's 1st law.
108.You throw a ball straight upward. Compared with its initial speed when thrown, how fast does it return to its starting point? Answer this for the case of no air resistance, and for the case where air resistance does affect motion.
It will return with the same amount of speed as the initial speed because when the object is thrown in the air, it will begin to start losing it's speed, and once it's speed arrives at 0, it will be at its highest point. It will then start gaining all that speed back on the way down because it took all that speed to get it up there and it began to lose that speed, so now, since it began to lose that speed per every second, it will also gain that speed per every second on the way down like counting down from 10 it would be like this with 0 being the highest point an d the negatives being the way down 10m/s, 9m/s, 8m/s, 7m/s, 6m/s, 5m/s, 4m/s, 3m/s, 2m/s, 1m/s, 0m/s, -1m/s, -2m/s, -3m/s, -4m/s, etc.
92.Suppose that a freely falling object were somehow equipped with a speedometer. By how much would its speed readings increase with each second of fall?
It would move at 10 meters per second squared. This is because all objects in the same vicinity on Earth that are in freefall have the same acceleration which is 10 meters per second squared. An object near Earth's surface will gain an acceleration of 10 m/s, so the speedometer would increase by 10 m/s for every second of freefall.
65.A space probe is carried by a rocket into outer space. A friend wonders what keeps the probe moving after the rocket no longer pushes it. What do you say?
It's inertia will keep it moving forever because on Earth, inertia would keep objects moving forever but it would be stopped by outside forces, friction, gravity, weight etc. In space, however, there is no gravity/weight or anything else. therefore, the object will just keep moving forever until some other force acts on it like a gravitational pull or a meteor hitting it. You say that the probe keeps moving because no force acts to slow it. The probe moves of its own inertia. Changes in motion require a force; no force, no change.
111.How does the gravitational force on a falling body compare with the air resistance it encounters before it reaches terminal velocity? After it reaches terminal velocity?
Just before a falling body attains terminal velocity, there is still a downward acceleration because gravitational force is still greater than air resistance. When the air resistance builds up to equal the gravitational force, terminal velocity is reached. Then air resistance is equal and opposite to gravitational force.
105.A rocket becomes progressively easier to accelerate as it travels through space. Why? (Hint: About 90% of the mass of a newly launched rocket is fuel.)
Let Newton's second law guide the answer to this; a=F/m. As m gets less (much the mass of the fuel), acceleration a increases while force remains constant.
67.What physical quantity is a measure of how much inertia an object has?
Mass
69.Is a person on a diet more accurately said to lose mass or to lose weight? Defend your answer.
Mass, because mass is the amount of matter in something, and you are trying to lose your fat, or lose matter. Weight, on the other hand is the force of gravity on an object. You can't change gravity by going on a diet. A person on a diet loses mass. To lose only weight, the person could go to the top of a mountain where gravity is less. But the amount of matter would be the same.
40.Find the strength of the net force produced by a 30
N force and a 20-N force in each of the following cases: Both forces act in the same direction. The two forces act in opposite directions.- A. 50 N B. 10 N
42.Madison pushes with a 160
N horizontal force on a 20-kg crate of coffee resting on a warehouse floor. The force of friction on the crate is 80 N. Show that the acceleration is 4.0 m/s2.-4m/s/s=80N/20kg
43.Sophia pushes with a 40
N horizontal force on a 4.0-kg box resting on a lab bench. The box slides against a horizontal friction force of 24 N. Show that the box accelerates at 4.0 m/s2.- a=Fnet/m=40 N−24 N/4.0 kg=16 N/4.0 kg=4.0 m/s2
115.When Marie exerts a horizontal force of 200 N to slide a table across a floor at constant velocity, how much friction does the floor exert on the table? Is the force of friction equal and oppositely directed to her 200
N push? Does the force of friction make up the reaction force to her push? Why or why not?- The friction on the table is 200 N, which cancels her 200-N push on the table to yield the zero net force that accounts for the constant velocity (zero acceleration). Although the friction force is equal and oppositely directed to the applied force, the two do not make an action-reaction pair of forces. That's because both forces do act on the same object—the table. The reaction to Marie's push on the table is the table's push back on her. The reaction to the frictional force of the floor on the table is the opposite friction force of the table on the floor.
82.Two 100
N weights are attached to a spring scale as shown. Does the scale read 0 N, 100 N, or 200 N, or some other reading? (Hint: Would the reading differ if one of the ropes were tied to the wall instead of to the hanging 100-N weight?)-
Suggest a bee and a bus make moving at a constant velocity collide, descrube what happens in terms of all of Newton's laws.
NEtwons 1st law states that an object will stay in it's state of motion unless acted on by an outside oforce. This means that the truck will keep going because it's inertia is greater so it will resist the change in motion. It will still have a change, just not as signifcant. Newtons second law staes that a/fnet/m. This means that the truck will have a lesser rate of change than the bee because accleration is inverely proportional to mass. tHis causes the truck to acclerate less and the bee to acelrate more. NEwton's 3rd la wstates that fpor every action there is an equal and oposite reaction. IN this case, the bus and the bee are exerting the same amount of force o n ecah other but the bu's inertia resists the bee's fporce more so it doesn't lokm like they are exerting the same amount of force on each other.
88.Gracie says acceleration is how fast you go. Alex says acceleration is how fast you get fast. They look to you for confirmation. Who's correct?
Neither are because acceleration is the rate at which velocity changes. Gracie was talking about speed, which is a factor of acceleration, but not what acceleration is. Alex said acceleration was how fast something gets fast, or how the rate of change of speed. Speed is not the same as velocity. Velocity is both speed and direction while speed is the distance per unit time. ALex described a component of acceleration but not the whole thing. Alex was closer though and if just said how fast an object's velocity changes, then he would be correct.
114.A farmer urges his horse to pull a wagon. The horse refuses, saying that to try would be futile, for it would flout Newton's third law. The horse concludes that it can't exert a greater force on the wagon than the wagon exerts on itself, so it wouldn't be able to accelerate the wagon. What explanation can you offer to convince the horse to pull?
Net force never comes out of a single ineraction ratehr it comes out of multiple ineractions acting together. Net force cpomes from forces applied to the ground in this instance. It is true though that you can only pull as hard on a horse as hard as the horse can pull back, but net force doesn't coem from that single interaction
What law explained what Galileo couldn't.
Newton's 2nd law of motion
99.Before the time of Galileo and Newton, many learned scholars thought that a stone dropped from the top of a tall mast on a moving ship would fall vertically and hit the deck behind the mast by a distance equal to how far the ship had moved forward during the time the stone was falling. In light of your understanding of Newton's laws, what do you and your classmates think about this idea?
Newton's first law again—when the stone is released it is already moving as fast as the ship, and this horizontal motion continues as the stone falls.
Every object continues in a state of rest, or in a state of motion in a straight line at constant speed, unless acted upon by a net force.
Newton's first law of motion
The acceleration produced by a net force on an object is directly proportional to the net force, is in the same direction as the net force, and is inversely proportional to the mass of the object.
Newton's second law of motion
Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first object.
Newton's third law of motion
80.The strong man will push apart the two initially stationary freight cars of equal mass before he alone drops straight to the ground. Is it possible for him to give either of the cars a greater speed than the other? Why or why not?
No because he is in the air and balancing from both of the cars. If he were to try to exert force on one of the cars, he would lose balance and cause himself to exert the same force on the other. It is like Newton's 3rd law of motion, which states that for every action, there is an equal and opposite reaction. He will do one action onto one, but will also do an equal and opposite action on the other one. He will push on one, which will cause him to push on the other one becaus eit is pushing back on him. He is a physical manifestation of NEwton's 3rd law
83.When you rub your hands together, can you push harder on one hand than on the other?
No, for each hand pushes equally on the other in accord with Newton's third law—you cannot push harder on one hand than the other.
119.Can a dog wag its tail without the tail in turn "wagging the dog"? (Consider a dog with a relatively massive tail.)
No, for in action-reaction fashion, the tail also wags the dog. How much depends on the relative masses of the dog and its tail, and friction between the ground and its feet.
96.Discuss whether or not a stick of dynamite contains force. Similarly, does a fist contain force? A hammer? Defend your answers.
None of these contain force becasue nothinhg can contain a force. They contain a lot of potential energy though, but no force. This is because of NEwton's 1st law. OUtside forces have to act on something to give it force.
53.A firefighter of mass 80 kg slides down a vertical pole with an acceleration of 4 m/s2. Show that the friction force that acts on the firefighter is 480 N.
Note that the weight of the 80-kg firefighter is mg = 80 kg × 10 m/s2 = 800 N. So Fnet = (800 N − f ) = ma = (80 kg)(4 m/s2) = 320 N. So f = 800 N − 320 N = 480 N.
97.In an orbiting space craft, you are handed two identical closed boxes, one filled with sand and the other filled with feathers. Discuss at least a couple of ways that you can tell which is which without opening the boxes.
Poke, kick, or shake the boxes. The one that more greatly resists a change in motion is the one with the greater mass—the one filled with sand.
formula for speed
S=D/T
Force
Simply stated, a push or a pull.
80.Place a heavy book on a table, and the table pushes up on the book. A friend reasons that the table can't push upward on the book because if it did, the book would rise above the table. What do you say to your friend? Why does this upward push not cause the book to rise from the table?
That is incorrect because the support force opposes with the same amount of force that the weight has. When you push the book down on the table, the table retaliates with the same amount of force as the weight of the book. If it didn't retaliate with force at all, the downward force of the book would cause the book to break through the table, through the ground, and to the center of the Earth. The support force stops when the table doesn't need support to stop the book form going through it or the table is not experiencing any more force pressed upon it.
94.Asteroids have been moving through space for billions of years. A friend says that initial forces applied long ago keep them moving. Do you and your friend agree?
That is true because all objects on earth would keep moving forever because of Inertia but are stopped by natural outside forces like friction, support force, etc. In space, however, there is no natural outside force to stop an object from moving so it will stay moving forever unless an outside force stops it. The object would've been completely still, but someone or something got it moving.
76.A friend says that Alé cannot push on the tree unless the tree pushes back on her, and another friend says that if Alé pushes quickly, the tree won't push as hard on her. Which friend do you agree with, and why?
The 1st friend is correct because Newton's 3rd law states that every action has an equal and opposite reaction, so if the action is that you push on the tree, the reaction is that the tree pushes back on you with an equal amount of force, hence why you don't go backwards from the tree pushing you and why you feel a pushing force when you push on the tree. Also why you won't push through the tree when you push on it.
As mentioned in the Prologue, the 16th-century Polish astronomer Copernicus caused great controversy when he published a book proposing that
The Earth reveolves around the sun
The greater the mass of an object, the stronger is the gravitational pull between it and Earth. The double brick in Figure 2.9 for example, has twice the gravitational attraction of the single brick. Why, then, doesn't the double brick fall twice as fast (as Aristotle supposed it would)?
The answer is evident in Newton's second law: the acceleration of an object depends not only on the force (weight, in this case), but on the object's resistance to motion—its inertia. Whereas a force produces an acceleration, inertia is a resistance to acceleration. So twice the force exerted on twice the inertia produces the same acceleration as half the force exerted on half the inertia.
100.Someone standing at the edge of a cliff (as in Figure 1.24) throws a ball straight up at a certain speed and another ball straight down at the same initial speed. If air resistance is negligible, which ball will hit the ground below at greater speed? Or will they both hit at the same speed?
The ball going straight down would because the other one that is thrown up in the air will take longer, but they will have the same speed when they hit the ground. The one thrown up in the air begins to lose all the force used to put it up there. It then begins to gain it all back through acceleration on the way down because gravity is now acting on it in it's direction. The other ball that was thrown straight down will head at the ground at the speed.
120.If you simultaneously drop a pair of tennis balls from the top of a building, they strike the ground at the same time. If one of the tennis balls is filled with lead pellets, will it fall faster and hit the ground first? Which of the two will encounter more air resistance? Defend your answers.
The ball with lead pellets ill hit the ground first because it has a lower surface area/weight ratio and terminal velocity is inversely proportional to the siurface area/weight ratio, this means the ball with pellets will reach it's maximum speed quicker than the ball without lea dpelets in it. It will also have mroe air resistance because air resistanc eis directly proportional to speed and surface area
In Figure 2.15, we see a boxer's fist hitting a massive punching bag. The fist hits the bag (and dents it) while the bag hits back on the fist (and stops its motion). This force pair is fairly large. But what if the boxer were hitting a piece of tissue paper?
The boxer's fist can exert only as much force on the tissue paper as the tissue paper can exert on the boxer's fist. The fist can't exert any force at all unless what is being hit exerts the same amount of reaction force
Descibe the events that take place when you fire a cannon
The cannon and the canon ball exert the sanme amount of force one ecahg other whe the cannon fires because of Newton's 3rd law, but thecannonball accelerates way than the other because of Newton's 2nd law that acceleration is inversely proportional to mass. MEanwhile, Newtons 2nd law also applies to the cannon noyt moving that much becaus eof it's high inertia. The way inertia works applies to Newton's 1st law.
Copernicus's concept of a Sun-centered solar system was the result of years of studying the motion of the planets. He had kept his theory from the public—for two reasons.
The first reason was that he feared persecution; a theory so completely different from common opinion would surely be taken as an attack on established order. The second reason was reservations about it himself; he could not reconcile the idea of a moving Earth with the prevailing ideas of motion. The concept of inertia was unknown to him and others of his time.
78.When you stand on a floor, does the floor exert an upward force against your feet? How much force does it exert? Why does this force not move you upward?
The floor does exert an upward force on you as you stand on it because Newton's 3rd law states that for every action, there is an equal and opposite reaction. When you stand on the floor the floor exerts a n opposite reaction of force to you standing in it. It exerts an equal amount of force on you as much as you exert on the floor because once again Newton's 3rd law states that for every action there is an equal and opposite reaction. Finally, the reason you are not moving upward is because it will always exert an equal and opposite reaction, so you will be put in equilibrium, mechanical equilibrium to be exact. WHen you are in mechanical equilibrium, you are stationary because the two forces acting on you are more than 0N and the net force of them is equal to 0N.
Weight
The force upon an object due to gravity. More specifically, the force with which a body presses against a supporting surface.
66.As you leap upward from the ground, how does the force that you exert on the ground compare with your weight?
The force you exert on the ground is the exact same as your weight which means the force exerted on you is the exact sae as the force you exert on the ground because Newton's 3rd law states that every action has an equal and opposite reaction. So if you were to exert 10 N on the Earth with a jump, the Earth would exert 10 N of gravitational force on you. I mentioned gravity because weight is the amount of gravity exerted on an object. So you are exerting force on the earth and the earth is exerting force back on you.
85.Consider the two forces acting on the person who stands still—namely, the downward pull of gravity and the upward support of the floor. Are these forces equal and opposite? Do they form an action-reaction pair? Why or why not?
The forces must be equal and opposite because they are the only forces acting on the person, who obviously is not accelerating. Note that the pair of forces do not comprise an action-reaction pair, however, for they act on the same body. The downward force, the man's weight, Earth pulls down on man, has the reaction man pulls up on Earth, not the floor pushing up on him. And the upward force of the floor on the man has the reaction of man against the floor, not the interaction between the man and Earth. (If you find this confusing, you may take solace in the fact that Newton himself had trouble applying his 3rd law to certain situations. Apply the rule, A on B reacts to B on A, as in Figure 2.19.)
68.For each of the following interactions, identify the action and reaction forces. (a) A hammer strikes a nail. (b) Earth gravity pulls down on a book. (c) A helicopter blade pushes air downward.
The hammer exerts force on the nail, which causes the nail to go downwards into whatever it is above. The reaction is that the nail exerts an equal force back on the hammer, hence why you feel an upward force when you hit the nail. Earth's gravity pulls down on the book which gives the book weight and causes it to push down. The reaction is that the book will exert an equal support force (the force that acts to oppose gravity.) on itself, which causes the book to remain stationary and not go through everything downwards.
63.Which of Aristotle's ideas did Galileo discredit with his inclined plane experiments?
The idea that all objects must have a force keeping them moving for them to keep moving. The incline plane experiments discredited the idea that a continuing force was needed for motion to continue.
99.In tearing a paper towel or plastic bag from a roll, discuss why a sharp jerk is more effective than a slow pull.
The inertia of a whole roll resists the large acceleration of a sharp jerk and only a single piece tears. If a towel is pulled slowly, a small acceleration is demanded of the roll and it unwinds.
63.Why is a massive cleaver more effective for chopping vegetables than a lighter knife of the same sharpness?
The more massive cleaver tends to keep moving when it encounters the resisting force of the vegetables, cutting them more effectively.
74.If the vine that supports the monkey breaks, what is then the net force on the monkey?
The net force is whatever the downard force is because the support force has been overpowered and is
Mass
The quantity of matter in an object. More specifically, a measure of the inertia (or sluggishness) that an object exhibits in response to any effort made to start it, stop it, deflect it, or change in any way its state of motion.
volume
The quantity of space an object occupies.
Acceleration
The rate at which velocity changes with time; the change in velocity may be in magnitude or direction or both, and it is usually measured in units of m/s2.
Friction
The resistive force that opposes the motion or attempted motion of an object past another object with which it is in contact, or through a fluid.
Newton
The scientific unit of force.
104.On which of these hills does the ball roll down with increasing speed and decreasing acceleration along the path? (Use this example if you wish to explain to someone the difference between speed and acceleration.)
The second one because it will be accelrating quickly at the beiginning and gaining speed, but when it arrives at the middle and the ground becomes less steep, it will slowly decrease accelration but accleration will still be happening on the ball because if it acc was 10m/s/s, the ball would increase 10m/s, when it decelerates to 9m/s/s the ball will be 19m/s it is not stopping but is decelerating.
velocity
The speed of an object and specification of its direction of motion.
67."It's not the fall that hurts you; it's the sudden stop." Translate this common saying into Newton's laws of motion.
The sudden stop involves a large acceleration. So in accord with a=Fm, a large a means a large F. Ouch!
79.An empty jug of weight W is at rest on a table. What is the support force exerted on the jug by the table? What is the support force when water of weight w is poured into the jug?
The support force on the jug is W. When water w is added, the support force is W + w.
101.Consider a ball at rest in the middle of a toy wagon. When the wagon is pulled forward, the ball rolls against the back of the wagon. A friend asks what force pushes the ball to the back of the wagon. Interpret this observation in terms of Newton's first law.
The tendency of the ball is to remain at rest. From a point of view outside the wagon, the ball stays in place as the back of the wagon moves toward it. (Because of friction, the ball may roll along the wagon surface—without friction the surface would slide beneath the ball.)
72.A monkey hangs stationary at the end of a vertical vine. What two forces act on the monkey? Which force, if either, is greater?
The two forces acting on the monkey are gravity and support force. The monkey is in equilibrium, which means neither force is greater because if the support force were higher, the monkey would be floating upwards, and if the downward force were higher, the vine would break. The monkey is in mechanical equilibirum because there are still forces acting on him, but he is not moving.
97.For the pulley system shown, what is the upper limit of the weight the strong man can lift?
The upper limit the man can lift is his own weight, for beyond that his feet leave the ground.
Equilibrium rule
The vector sum of forces acting on an object that is not accelerating equals zero
51.If you stand next to a wall on a frictionless skateboard and push the wall with a force of 40 N, how hard does the wall push on you? Show that if your mass is 80 kg, your acceleration is 0.5 m/s2 away from the wall.
The wall pushes on you with 40 N. a=Fnet/m=40 N/80 kg=0.5 m/s2.
84.One ultralight aircraft travels due north at 100 km/h while another travels due south at 100 km/h. Are their speeds the same? Are their velocities the same? Explain.
Their speeds are the same, but their velocity is not. Speed is only the distance per unit time, while velocity is speed and direction. They may have the same speed, but one is moving south and the other is moving north. Velocity has to have both the direction and the speed for it to be velocity. If it has the same speed but different directions, the velocity is different. If it has the same direction but different speeds, the velocities are different as well. This means the speed is the same, but the velocity is different.
93.A racing car travels along a straight raceway at a constant velocity of 200 km/h. What horizontal forces act, and what is the net force acting on the car?
There are two horizontal forces on the car: road friction acting on the tires, and air resistance in the opposite direction. At constant velocity there is no acceleration. The net force is therefore zero—meaning the force on the tires is equal and opposite to the force of air resistance.
90.What is the acceleration of a car that moves at a steady velocity of 100 km/h for 100 s? Why is this question an exercise in careful reading as well as in physics?
There is no acceleration because a steady or constant velocity doesn't accelerate.
two balls roll down hill. one is heavy, one is light. they roll down the hill at the same time. Why?
They roll at the same force/mass ratio
118.Ken and Joanne are astronauts floating some distance apart in space. They are joined by a safety cord whose ends are tied around their waists. If Ken starts pulling on the cord, will he pull Joanne toward him, or will he pull himself toward Joanne? Explain what does happen.
They will both head to the middle of the rope because of newton's 3rd law. If one had more mass than the ptehr they would meet closer to whoever has the more mass (Newton's 1syt law)
88.Suppose that one of the people in Exercise 87 has twice the mass of the other. How far does each person slide before they meet?
They will slide more towards the left if the astronuat with twice the mass of the otehr is on the ,eft because the greater mass the greater the inertia and the greater the inertia, then more resistance in changing a form of motion. Newton's 2nd LAw and NEwton's 1st law. Newtons 3rfd Law.
76.When you push downward on a book that is at rest on a table, you feel an upward force. Does this force depend on friction? Defend your answer.
This force does not depend on friction because friction is an opposing force when an object is pushed passed another through contact or through a fluid. The book is pushed against the table over past it. The force that is actually acting on the object is the support force. Support force is the upward force that opposes gravity. You are pushing the book downward like gravity is pushing everything else downward, so the support force is countering that by pushing upwards, which is the force you are feeling when you push the book on the table.
Describe the ascent from the first floor of an elevator to the 4th floor while you stand on a scale
We start at the bottom and you read your weight. The elevator is motionless. It then begins to shift from the bottom floor to the first you then begin to gain speed and the scale read more than your weight becuse your inertia is resisting the change in motion. From the first floor to the 3rd floor, you will be moving at a constant velocity and you will read your original weight. When you get from the 3rd to the 4th floor, you begin to slow down andthe scale reads less than your orginal weight becasue your inertia is still going up. When you finally reach the 4th floor, the elevatyor will be ata a stop and your weight will read it's original agaon.
39.A Honda Civic hybrid weighs about 2900 pounds. Calculate the weight of the car in newtons and its mass in kilograms. (FYI, 0.22 lb = 1 N; 1 kg on Earth's surface has a weight of 10 N.)
Weight in newtons: 2900lb×1N/0.22 lb=13,182 N. Mass in kg: 13,182 N×1 kg/10 N=1318 kg.
72.Free fall is motion in which gravity is the only force acting. (a) Explain why a skydiver who has reached terminal speed is not in free fall. (b) Explain why a satellite circling Earth above the atmosphere is in free fall.
When a skydiver is in terminal speed, his velocity equals air resistance, so he is not getting faster or slower, he is as fast as he can go. He is not in free fall because air resistance is acting on him and pushing upwards enough to add an equal amount of force upwards to the amount of force downwards. The satallite on the other hand
103.Why do you lurch forward in a bus that suddenly slows down? Why do you lurch backward when it picks up speed? What law applies here?
When the bus slows, you tend to keep moving at the previous speed and lurch forward. When the bus picks up speed, you tend to keep moving at the previous (lower) speed and you lurch backward. The law of inertia applies in both cases.
95.When you toss a coin upward, what happens to its velocity while it is ascending? What happens to its acceleration? (Neglect air resistance.) What is its acceleration at the top of its path?
When the coin goes up the velocity decreases by 10 m/s each second. Its acceleration, however, remains constant (which is why the constant change of 10 m/s each second). At the top its acceleration is 10 m/s2.
79.Why can you exert greater force on the pedals of a bicycle if you pull up on the handlebars?
When you pull up on the handlebars, the handlebars in turn pull down on you. This downward force is transmitted to the pedals.
113.This is a scenario common to many physics students: You push a heavy car by hand. The car, in turn, pushes back with an opposite but equal force on you. Doesn't this mean that the forces cancel one another, making acceleration impossible? Resolve the misunderstanding underlying this question.
When you push the car, you exert a force on the car. When the car simultaneously pushes back on you, that force is on you—not the car. You don't cancel a force on the car with a force exerted on you. For cancellation, the forces have to be equal and opposite and act on the same object. Two equal and opposite forces would have to act on the car for cancellation.
102.If you're in a car at rest that gets hit from behind, you can suffer a serious neck injury called whiplash. Discuss how whiplash involves Newton's first law and why headrests are standard on today's cars.
Whiplashes are like Newton's first law of motion. Newton's 1stb law of motion states that an object will remain in its state of motion unless acted upon by an outside force. This way, when an object suddenly exerts a large amount of force from moving fast like when stepping on the gas in a car or being rear ended, you will suddenly jerk backwards from the high sudden force you just generated with the car. This will cause your neck to build up a huge amount of inertia because of the sudden high force and pull back, now it is like pulling hard a paper towel roll. Only part of your neck will jerk forward so it will hurt badly. Headrests are now in cars so when a car goes fast instead of jerking backwards, you will just exert a force on the headrest and thanks to Newton's 3rd law of motion (all actions have equal and opposite reactions) your head will be stationary and not whip;lash you.
94.If it were not for air resistance, would it be dangerous to go outdoors on rainy days? Defend your answer.
Yes because of Newton's 1st and 3rd law of motion. His first law states that any object in motion stays in motion unless acted upon by an outside force. His third law states that every action has an equal and opposite reaction. This means that when the object is falling, air resistance or an outside force builds up to equal out the force of the rain droplets, thus making them have low speed when falling. Without this, the rain would keep increasing more and more and more until it is at a crazy speed when it hits the ground. It would move like a bullet and definitely hurt when it hits you.
75.We know that Earth pulls on the Moon. Does it follow that the Moon also pulls on Earth?
Yes, both pulls make up an interaction; neither can exist without the other. Earth cannot pull on the Moon unless Moon simultaneously pulls on Earth.
98.Each of the vertebrae forming your spine is separated from its neighbors by discs of elastic tissue. Each step you take acts on your spine like a small jump. Can you think of a reason why you are a little shorter in the evening than you are in the morning? (Hint: Think about the hammerhead in Figure 2.2.)
You are shorter in the evening because the force of inertia is acting in your vertebrates. Newton's 1st law of motion states that every object will stay in its position of motion until it is acted upon by an outside force. This is because of something called inertia which is an object's tendency to resist changes in motion. So, your vertebrates will begin to start building up inertia becasue of gravity pulling down on you the more steps you take and begin to make the small jumps less by pulling down on them to hold them into place and eventually bring them to a stationary position as they were meant to be. SInce they are pulled back down, your height shortens.
61.To pull a wagon across a lawn at constant velocity, you must exert a steady force. Reconcile this fact with Newton's first law, which states that motion at constant velocity indicates no force.
You exert a force to overcome the force of friction. This makes the net force zero, which is why the wagon moves without acceleration. If you pull harder, then net force will be greater than zero and acceleration will occur.
91.When your car moves along the highway at constant velocity, the net force on it is zero. Why, then, do you continue running your engine?
You run your engine to provide a force large enough to overcome friction. A net force of zero requires you provide this force.
62.Your empty hand is not hurt when it bangs lightly against a wall. Why does your hand hurt when it bangs against the wall while carrying a heavy load? Which of Newton's laws is most applicable?
You will have more mass on yourself with the bowling ball in hand which give syou more inertia. Inertiqa is an objects tendancy to resist chanegs in motion. This means when you collide with thye wall, the inertia you have will cause your hand to exert the same amount of force on the fall soon because when you use just your hand, the you have less inertia so the wall stops you form hurting yourself by exerting force. Whe you use a bowling ball the inertia is more so the wall has more truble stopping you so you exeet the force still and possibly hrut your hand by forcing it hard on the wall.
95.In answer to the question "What keeps Earth moving around the Sun?" a friend asserts that inertia keeps it moving. Correct your friend's erroneous assertion.
Your friend should learn that inertia is not some kind of force that keeps things like Earth moving, but is the name given to the property of things to continue as they are doing when no external force acts. So your friend should say that nothing is necessary to keep the Earth moving. Interestingly, the Sun keeps it from following the straight line path it would take if no forces acted, but it doesn't keep it moving. Nothing does. That's the concept of inertia. We distinguish between what makes an object begin moving, and what keeps it moving.
how do those 4 things go hand in hand
Zero net force is the definition of equilibriyum, equilibium not accelrationg, zero accelration is moving at a constant veloicty, moving with 0 accelration, but there are still two forces actng on it that cancel each other out, giving you zero accelration.
61.Three pucks, A, B, and C, are sliding across ice at the noted speeds. Air and ice friction forces are negligible. (a) Rank, from greatest to least, the force needed to keep the pucks moving. (b) Rank, from greatest to least, the force needed to stop them in the same time interval.
a. A=B=C (no force) b. C, B, A
in x=a/b x is directly proportional to ___ and inversely proportionl to ____
a. B.
formula for terminal velocity
a=Net force/m=mg-R/m
35.In Chapter 1 acceleration is defined as a=ΔvΔt. Show that on an inclined plane, the acceleration of a cart that gains 6.0 m/s each 1.2 s is 5.0 m/s2.
a=Δv/Δt=6.0 m/s/1.2 s=5.0 m/s2
40.When two horizontal forces are exerted on the car in Problem 39, 220 N forward and 180 N backward, the car undergoes acceleration. What additional force is needed to produce non
accelerated motion?-40 N backwards
Most moving things undergo variations in their motion. We say they undergo
acceleration
Newtons second law of motion in equation form
acceleration=net force/mass
We can call one force the _________ and the other the _____________reaction force
action force; reaction force
R stands for
air resistance
Galileo said (in absence of air drag)
all objects regardless of weight fall at the same rate.
what led newton to make the law of universal gravitiation
an apple falling from a tree
Why is continues the key word in Newton's first law
an object continues to do whatever it happens to be doing unless a force is exerted upon it. If the object is at rest, it continues in a state of rest.On the other hand, if an object is moving, it continues to move without changing its speed or direction,
the acceleration of free fall is independent of
an objects mass
110.How does the terminal speed of a parachutist before opening a parachute compare to the terminal speed after opening a parachute? Why is there a difference?
before opening the parachute you have a faster terminal velocity because you have a lower surface area/weight ratio. When you deploy your parachute, you have a higher surface area/weight ratio
Constant velocity, on the other hand, means
both constant speed and constant direction.
56.In cases A, B, and C, the crate is in equilibrium (no acceleration). Rank, from greatest to least, the amounts of friction between the crate and the floor in these three cases.
c,b,a
Galileo measured speed by
comparing the distance covered with the time it takes to move that distance.
To better understand that the table pushes up on the book, compare the case of compressing a spring (Figure 1.13). If you push the spring down, you can feel the spring pushing up on your hand. Similarly, the book lying on the table
compresses atoms in the table, which behave like microscopic springs. The weight of the book squeezes downward on the atoms, and they squeeze upward on the book. In this way, the compressed atoms produce the support force.
The key word in this Newton's first law of motion is
continues
When something slows down, we often call this
deceleration
Directly and inversely proportional is like saying
directly/indirectly negligable
Speed is directly proportional to
distance
how did Galileo experiment work
dropped two objects with the same surface area/weight ratio off the leaning tower of Piza, fell at the same time and hiy the ground at the same time.
But the state of rest is only one form of equilibrium. An object moving at constant speed in a straight-line path is also in equilibrium. We say it's in
dynamic equilibrium
Quite interestingly, a falling object pulls upward on Earth with as much force as
earth pulls down on it
Unlike most concepts in physics, friction is a very complicated phenomenon. The findings are __________ (gained from a wide range of experiments) and the predictions are ___________ (also based on experiment).
empirical; approximate
Isaac Newton was the first to realize the connection between
force and mass in producing acceleration, which is one of the most central rules of nature.
55. Boxes of various masses are on a friction
free level table. (a) Rank, from greatest to least, the net forces on the boxes. (b) Rank, from greatest to least, the accelerations of the boxes.-a. D, A = B = C b. A = C, B = D
fluid friction
friction that occurs as an object moves through a fluid (including air)
rolling friction
friction that occurs when an object rolls over a surface
sliding friction
friction that occurs when one solid surface slides across another
aristotle didn't understand the
fundementals
Galileo couldn't say why all bodies fall equally because
he never connected the concepts he developed—acceleration and inertia—with force.
Four hundred years ago, people had difficulty with ideas like these. One reason is that
hey didn't yet travel in high-speed vehicles. Rather, they experienced slow, bumpy rides in horse-drawn carts.
This pair of forces, your pull on the cart and the cart's pull on you, make up the single interaction between you and the cart. Such observations led Newton to
his 3rd law of motion
When Galileo allegedly dropped objects of different weights from the Leaning Tower of Pisa, they didn't actually
hit at the same time
86.You're in a car traveling on a highway at some specified speed limit. You see another car moving at the same speed directly toward you. How fast is the car approaching you, compared with the speed limit?
however fast the speed limit says because from it's veiw, it is travelling as fast as you are, and you are traveling ask fast as the speed limit says for you to be.
Interestingly, an object under the influence of only one force cannot be
in static or dynamic equalibrium
speed at any instant
instantaneous speed
surface area to weight ratio is _______ proportional
inversely
41.A 120
kg astronaut recedes from her spacecraft by activating a small propulsion unit attached to her back. The force generated by a spurt from this device is 30 N. Show that her acceleration is 0.25 m/s2.- a=Fnet/m=30 N/120 kg=0.25m/s2
65.What is the net force acting on a 1
kg ball in free fall? What is the net force if it encounters 2 N of air resistance?- The net force is mg, 10 N (or more precisely, 9.8 N). With air resistance the net force is 10 N − 2 N = 8 N (or more precisely 9.8 N − 2 N = 7.8 N).
57.Consider a 100
kg box of tools in the locations A, B, and C. (a) Rank, from greatest to least, the masses of the 100-kg box of tools. (b) Rank, from greatest to least, the weights of the 100-kg box of tools.-a. A = B = C b. C, A, B
36.In this chapter we learn that the cause of acceleration is given by Newton's second law: a=Fnetm. Show that the acceleration in Problem 35 results from a net force of 15 N exerted on a 3.0
kg cart. (Note: The unit N/kg is equivalent to m/s2.)-5m/s/s=15N/13kg
68.Which has more mass: a 2
kg fluffy pillow or a 3-kg small piece of iron? Which has more volume? Why are your answers different?- The 3 kg small piece of iron has more mass, while the 2 kg king sized pillow has more volume. The reason these two answers are the way they are is because mass is not the same as volume. Volume is just how much space an item takes up, while mass is the amount of matter in an object. The piece of iron has more mass because unlike the pillow, it is more solid, making it have more matter inside of it, while a pillow is not very solid. It rather has multiple pieces inside of it, so it has less matter. Meanwhile, a pillow has more volume because it is bigger or takes up more space than the small piece of iron. Size is not indicative of mass. The small peaice of iron has more atoms. COmpressed into small peice
71.Gravitational force on the Moon is merely ⅙ the gravitational force on Earth. What would be the weight of a 10
kg object on the Moon and on Earth? What would its mass be on the Moon and on Earth?- 4.55 on Earth, 0.77 on the Moon. It would be 10 kg on Earth and on the moon because unlike gravity, mass never changes because the amount of matter something has never changes. The weight of a 10-kg object on Earth is about 100 N, and on the Moon 1/6 of this, or nearly 17 N. The mass would be 10 kg on the Moon, Earth, or any location.
37.Knowing that a 1
kg object weighs 10 N, confirm that the acceleration of a 1-kg stone in free fall is 10 m/s2.- a=Fnet/m=10 N/1 kg=10 N/kg=10 m/s2
38.A simple rearrangement of Newton's second law gives Fnet = ma. Show that a net force of 84 N exerted on a 12
kg package is needed to produce an acceleration of 7.0 m/s2. (Note: The units kg·m/s2 and N are equivalent.)- 84N=12kg*7m/s/s
46.Calculate the horizontal force that must be applied to a 1
kg puck for it to accelerate on a horizontal friction-free air table with the same acceleration it would have if it were dropped and fell freely.- 10N
48.For 3.0 s, Allison exerts a net force of 10.0 N on a 6.7
kg shopping cart that was initially at rest. Find the acceleration of the cart, and show that it moves a distance of 6.7 m.- 0.7m/s/s
Newton's first law of motion, usually called the
law of inertia,
107.Two balls, A and B, are released simultaneously from rest at the left end of the equal
length tracks A and B, as shown. Which ball, A or B, will reach the end of its track first?- Ball B reaches the end of its track first, for its average speed along the lower part as well as the sloped parts is greater than the average speed of the ball A along the straighter track A.
lighter
less speed. easier to get going
106.If you toss a coin straight upward while riding in a train that travels at uniform and steady motion along a straight
line track, where does the coin land? Where does the coin land if the train slows while it is tossed? Where does it land if the train rounds a curve?-It will land in the palm of your hand because it is already moving as fast as the train and so are you. When you toss it in the air, it is like a plane moving upwards and downwards while moving. From a still frame of reference the coin is like the plane compared to it, but compared to you, it is only moving up then down. If the train slows down the coin will land in front of you because it is still moving at a high speed and is still moving in mid air, so when the train stops it you will see it has been moving and it will stop moving afterwards because unlike you, the train is not touching it. If the train turns then the coin will land in the direction opposite of where the train turned because it is moving straight and the train is turning. Horizantal an Vertical are independent of each other. Newton's first law of inertia-all motion is relative
Aristotle used ________ to establish his ideas of motion, whereas Galileo used ___________.
logic; experiment
116.Two equal
mass blocks are connected by a length of string. One block is placed at rest on a very smooth table, and the other block dangles off the table's edge. You hold the blocks so they don't move. When released, the hanging one accelerates downward, pulling the top block horizontally across the table. Why do both blocks undergo the same amount of acceleration? Show that this acceleration ideally is one-half g.-
When the net force on something is zero, we say that the object is in
mechanical equalibrium
This upward support force, often called the
normal force
there is no way that an object can exert a force on
nothing
87.Two people of equal mass attempt a tug
of-war with a 12-m rope while standing on frictionless ice. When they pull on the rope, each person slides toward the other. How do their accelerations compare, and how far does each person slide before they meet?-The forces on each are the same in magnitude, and their masses are the same, so their accelerations will be the same. They will slide equal distances of 6 meters to meet at the midpoint.
89.Which team wins in a tug
of-war: the team that pulls harder on the rope, or the team that pushes harder against the ground? Explain.- The winning team pushes harder against the ground. The ground then pushes harder on them, producing a net force in their favor.
86.If a Mack truck and a motorcycle have a head
on collision, upon which vehicle is the impact force greater? Which vehicle undergoes the greater change in its motion? Defend your answers.- They will have equal impact fporce because of NEwton's 3rd law. The motorcycle will have a greater cahnge in accelration because the truck has a lot more mass than the motorcycle (Newton's 2nd law and NEwton's 1st LAw)
inversely proportional
one goes up other goes down
directly proportional
one goes up other goes up
Again, for emphasis: friction always acts in a direction to _________ motion.
oppose
An interaction requires a _______ of forces acting on _________ objects
pair; two
---------> ^ |
perpendicular net force
It was his experiments with _______ that first made him famous.
prisms
If action is A acting on B
reaction is B acting on A
When a skydiver steps from a high-flying plane, the air resistance on the skydiver's body builds up as the falling speed increases. The result is
reduced acceleration. The acceleration can be reduced further by increasing frontal area.
all motion is
relative
Newtons connection between these two things was expressed in his
second law of motion
E (sideways M)means
sigma
Consider the interesting demonstration of the falling coin and feather in the glass tube (Figure 2.13). When air is inside, we see that the feather falls more ___________ due to air resistance. The feather's weight is very small, so it reaches terminal speed _________.
slowly; quickly
42.Henry Heavyweight weighs 1200 N and stands on a pair of bathroom scales in such a way that one scale reads twice as much as the other. What are the scale readings?
smaller one:400N bigger one: 800 N
Friction occurs for
solids liquids and gases
Any combination of units for distance and time can be used for
speed
Moving things often have variations in
speed
Air resistance depends primarily on two things:
speed and frontal area
105.Because Earth rotates once every 24 hours, the west wall in your room moves in a direction toward you at a linear speed that is probably more than 1000 km per hour (the exact speed depends on your latitude). When you stand facing the wall, you are carried along at the same speed, so you don't notice it. But when you jump upward, with your feet no longer in contact with the floor, why doesn't the high
speed wall slam into you?- When you jump, your horizontal motion matches that of Earth, and no force acts on you to change that. Hence, you travel along with Earth.
When an object remains stationary, the forces on it add up to zero—it's in equilibrium. More specifically, we say it's in
static equalibrium
Constant speed means
steady speed, neither speeding up nor slowing down.
Friction is due to tiny surface bumps and also to the ________ of the atoms on the surfaces of the two materials
stickiness
71.Why does a cat that falls from the top of a 50
story building hit a safety net below no faster than it would if it fell from the 20th story?-The terminal speed attained by the falling cat is the same whether it falls from 50 stories or 20 stories. Once terminal speed is reached, falling extra distance does not affect the speed. (The low terminal velocities of small creatures enable them to fall without harm from heights that would kill larger creatures.)
Constant direction is a
straight line—the object's path doesn't curve.
Galileo was one of the first to build a _________, and the first to direct it to the ___________ ___________ and discover mountains on the _______ and the moons of __________.
telescope; nightime sky; Moon; Juptier
Terminal speed in a given direction (often downward).
terminal velocity
average speed is
the entire distance covered divided by the total time travelled
he fact that the net force on the desk equals zero means that
the force of friction must be equal in magnitude and act opposite to our pushing force.
tention
the force that is transmitted through a rope, string or wire when pulled by forces acting from opposite sides.
For a suspended object at rest, like the bag of flour, the rule states that
the forces acting upward on the body must be balanced by other forces acting downward to make the vector sum equal zero. (
what would a police offucer be comparing your car to when using a speed taker thing
the ground
We see that the distance of free fall from rest is directly proportional to
the square of the time of fall
Statement to be memorized
these things go hand in hand with each other: zero accelration, equilibium, constant velocity, zero net force
Speed is inversely proportional to
time
Formula for average speed
total distance/total time= average speed
Every contact requires at least a
twoness
Velocity is a
vector quantity
EF=
vector sum of forces
When straight-line motion is being considered, we can use the words __________ and _________ interchangeably in the definition of acceleration
velocity
factors of fluid friction
viscosity- how hard it is to go through something speed- how fast someting is going surface- shape of something or what something is made of
mg stand for
weight
velocity is directly proportional to
weight
frame of reference
what we compare moving objects to
Although Galileo founded the concepts of both inertia and acceleration and was the first to measure the acceleration of falling objects, he was unable to explain
why objects of various masses fall with equal accelerations.
This exhilarating sport, __________, goes beyond what flying squirrels can accomplish, since a flyer can achieve horizontal speeds appreciably greater than 170 km/h (100 mph).
wingsuit flying
if action and reaction forces are equal and opposite, why don't they cancel to zero?
you cant cancel the fprce pn one thing with a force on the other