ch 1-4 physical science
Your friend says that impulse equals momentum. This statement isn't correct, and the missing word is
change (should say that impulse equals the change in momentum)
A satellite in elliptical orbit about Earth travels fastest when it moves
close to earth
Constant speed in a constant direction is
constant velocity.
A machine can multiply forces or
distances
Vertical distance formula
d = 1/2gt^2
If the distance between two planets doubles, the force of gravity between them
decreases to one-quarter
When the mass of an object is compared to its volume, the concept is
density
The difference between speed and velocity mostly involves
direction
Whereas impulse involves force and time, work involves force and
distance
When a ball is tossed straight upward, the direction of its acceleration is
downward, toward Earth's center.
Gravity was discovered by
early humans
When a cannonball is shot from a cannon, the cannon recoils. Compared with the momentum given to the cannonball, the momentum of the recoiling cannon is ideally
equal and opposite.
When you stand at rest on a weighing scale, the force due to gravity on you is
equal in magnitude to the support force of the scale.
When an airplane flies horizontally at constant speed in a straight line, the air drag on the plane is
equal to the amount of thrust.
The concept of free-falling objects applies to
falling apples and moon
Acceleration formula
final velocity-initial velocity/time
Seat belts and air bags in a car are mostly linked to the effects of Newton's
first law. (inertia. Every object will remain at rest or in uniform motion in a straight line unless acted on)
A moving freight car slams into another identical freight car at rest. The two cars stick together and move along the track. The speed of the coupled cars compared with the initial speed of the first car is
half
When Nellie Newton hangs by a pair of vertical ropes, the tension in each rope will be
half her weight.
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.
With air resistance, the time for a vertically tossed ball to return to where it was thrown from is
more than the time going upward (Consider a feather tossed upward. It reaches its zenith rather quickly but falls back to its starting place slowly. The same is true of a ball tossed in air, though not as pronounced.)
When you jump vertically upward, strictly speaking, you cause Earth to
move downward. (When you jump upward, you push downward on Earth. Strictly speaking, it therefore moves downward. By how much? Not much, in fact negligibly, because its mass is so much greater than yours.)
The first person(s) to publish writings about Earth satellites was
newton
The laws of physics that were employed to get humans to the Moon are
newtons law of motion (As the concluding paragraph of Chapter 2 states, Newton's laws were and are sufficient for getting humans to the Moon!)
The speed of a bowling ball rolling along a smooth alley is
not affected by gravity and constant.
The force that directly propels a motor scooter along a highway is that provided by the
road (The tires push back on the road, and in so doing, the road pushes forward on the tires. It is this force that is directly responsible for the scooter's motion.)
A grasshopper has a head-on collision with a speeding Mack truck. The greatest force acts on the
same amount on each (Although the forces are equal in magnitude, the effects of these forces are drastically different. Don't confuse something with the effects of that something.)
A falling object that reaches terminal velocity continues to have
speed (At terminal velocity, both net force and acceleration are zero)
When you toss a rock straight upward, which is no longer present at the top of its path?
speed (It still has a force on it, mg, so a = F/m = mg/m = g. Only speed is zero at the top.)
A body undergoes acceleration whenever there is a change in its
speed, velocity, direction
According to the equation for gravity, if you travel far enough from Earth, the gravitational influence of Earth will
still be there
When an astronaut in orbit around Earth is weightless, he or she is
still in the grip of Earth's gravity.
When you jump from an elevated position to the ground below, the kinetic energy you have when you meet the ground depends on
the jumping height
The force of friction between materials sliding against each other depends on
the kind of materials , the roughness of the materials, and the force with which they are pressed together.
When a blank is fired from a pistol, although no bullet emerges, hot gases due to the firing do emerge. Compared with the momentum of the recoiling pistol, the momentum of these gases is
the same (Momentum conservation illustrated. More than one person has been killed by gases from a closely held gun shooting blanks.)
A soccer ball is kicked to a 30-m/s speed. While being kicked, the amount of force of the player's foot on the ball is
the same as the amount of force on the foot( speed is irrelevant according to newtons 3rd law)
Without air resistance, the time for a vertically tossed ball to return to where it was thrown from is
the same as the time going upward.
The mass of 1 kilogram of iron
the same on the moon (mass doesn't change/ only weight)
Newtons 1st law
(Law of Inertia) an object in motion tends to stay in motion & an object at rest stays at rest unless acted upon by an outside force.
A pair of 3-N and 4-N forces CANNOT have a resultant of
0 N, When parallel, the two vectors can add to 7 N or subtract to 1 N. They cannot cancel to zero.
When a 10-kg block is simultaneously pushed eastward with 20 N and westward with 15 N, the acceleration of the block is
0.5 m/s2 east.(Note the mass of a 10-N block is about 1 kg. Then a = F/m = (20 N - 15 N)/1 kg = 0.5 m/s2.)
The amount of air resistance on a 0.8-N flying squirrel for terminal speed is
0.8-N (For terminal speed, net force must equal zero, no matter what the orientation of the squirrel's body. How great the terminal speed is does depend on body orientation. But that's not the question asked.)
A 1-kg ball has twice as much speed as a 10-kg ball. Compared with the 1-kg ball, the 10-kg ball has
5 times as much momentum (Momentum of 1-kg ball = m(2v) = 2 mv.Momentum of 10-kg ball = (10m)v = 10 mv.)
When a ball rolling down an inclined plane gains 4 m/s each second, the acceleration of the ball is
4 m/s2.
When you stand on two bathroom scales, with more weight on one scale than on the other, the readings on both scales will
will add to equal your weight
The net force on any object in equilibrium is
zero
When a bird flies at 8 km/h in an 8-km/h headwind (moving against the wind), the speed of the bird relative to the ground is
zero
When no air resistance acts on a projectile, its horizontal acceleration is
zero
If you drop a boulder from a tall cliff, as it falls it will gain
10 m/s of speed each second. ( rounded gravity 9.81 for free fall, will not vain more and MORE since its not accelerating)
A 1-kg iron ball and a 10-kg iron ball are dropped from rest from the top of a one-story building. When hitting the ground below, compared with the 1-kg ball, the 10-kg ball has
10 times as much momentum and 10 times as much KE. (Both have equal speeds. Both momentum and KE are directly proportional to mass.)
A 100-kg vehicle accelerates at 1 m/s2 when the net force on it is
100 N (From a = F/m, simple rearrangement gives:F = ma = (100 kg)(1 m/s2) = 100 N.)
After being dropped from the top of a high building, a free-falling object has a speed of 30 m/s at one instant. Exactly 1 second earlier, its speed was
20 m/s (A free-falling object changes its speed by 10 m/s each second. 30 m/s - 10 m/s = 20 m/s. If it were moving upward, technically still in "free fall," its speed 1 second earlier would be 40 m/s.)
The impulse-momentum relationship is a direct result of Newton's
2nd law (Equate Newton's second law a = F/m to v/ t and get F/m = v/ t. From this, F t = (mv). Calling t simply the time interval t, we get Ft = mv.)
The connection between mass, acceleration, and force is embodied in Newton's
2nd law (the acceleration of an object is dependent upon two variables - the net force acting upon the object and the mass of the object.)
A karate chop delivers a blow of 3500 N to a board that breaks. The force that acts on the hand during this event is
3500N
A pair of parallel forces of 8 N and 12 N can have a resultant of
4 N and 20 N =When parallel, 12 N + 8 N = 20 N, or 12 N - 8 N = 4 N.
If a motor vehicle increases its speed by 4 km/h each second, its acceleration is
4 km/h per second.
Arnold Strongman and little Nellie Newton have a tug-of-war. The greatest force on the rope is provided by
Both the same, interestingly enough.( The winner of a tug-of-war is the one who pushes harder against the ground)
Which of the following equations best illustrates the usefulness of automobile air bags?
Ft = mv (Extend the time, decrease the force.)
The concept of inertia is attributed to
Galileo and Newton.
If the speed of a racing car doubles, what else doubles?
Its momentum.(Note that momentum is proportional to speed, but kinetic energy is proportional to speed squared.)
describe newtons 2nd law
Newton's Second Law of Motion states that when a force acts on an object, it will cause the object to accelerate. The larger the mass of the object, the greater the force will need to be to cause it to accelerate. This Law may be written as force = mass x acceleration or: F = m * a
newtons third law explained
Newton's Third Law of Motion states that for every action, there is an equal and opposite reaction.
A hungry bee looking directly ahead sees a flower in a 5-m/s breeze. When it gets to the flower, how fast and in what direction should it fly in order to hover above the flower?
The bee should fly 5 m/s into the breeze. (When just above the flower, it should fly at 5-m/s into the breeze in order to hover at rest. This is why bees grip onto a flower to prevent from being blown off.)
A cart is pushed and undergoes a certain acceleration. Consider how the acceleration would compare if it were pushed with twice the net force while its mass increased by four. Then its acceleration would be
Twice the force acting on four times the mass gives half the acceleration. So the acceleration would be half
When a car rounds a curve, it is
accelerating ( speed is a scalar and acceleration is vector)
Anthony is late for class and is soon reprimanded. Causes lead to consequences. We can show, however, that this is not an example of Newton's third law because
action and supposed reaction are not simultaneous.
As a flying squirrel falls faster and faster through the air,
air resistance increases, net force decreases, acceleration decreases
When standing in the aisle of a smoothly riding bus, you drop a coin from above your head. The falling coin will land
at your feet (The horizontal velocity of the coin remains the same as it falls.)
A satellite in orbit around the Earth is above Earth's
atmosphere (Don't say above Earth's gravitational field! If it were, it wouldn't circle Earth.)
A heavy parachutist has a greater terminal speed compared with a light parachutist with the same size chute, because the heavier person
has to fall faster for air resistance to match his weight(At terminal speed, both weight and air resistance have the same magnitude. To get that greater magnitude of air resistance, falling speed has to be greater for the heavier person.)
When a car is braked to a stop, unless it is a hybrid, its kinetic energy is transformed to
heat
When air resistance is negligible, the component of velocity that doesn't change for a projectile is the
horizontal component.(That's because there is no horizontal force)
acceleration saying
how fast you get fast
A ball initially at rest rolls along a pair of equal-length tracks A and B. It will roll faster when
in the dip of track B
When the distance between two stars decreases by one-tenth, the force between them
increases 100 times as much (This refers to the inverse-square law of gravity. Ten times closer means 100 times the force.)
The kind of speed you read on a speedometer is
instantaneous speed
If both the mass and speed of an object are doubled, its momentum
is quadrupled.
When we say that 1 kilogram weighs 10 N, we mean that
it's true at Earth's surface.
If an object has momentum, it must also have
kinetic energy (Anything with speed has both momentum and kinetic energy.)
Strictly speaking, compared with your weight on the ground, your weight at the top of a very tall ladder would be
less
The longest that anyone in your school can be in the air when jumping straight upward, landing at the same place, is
less than 1 second.( you would have to generate a velocity of 9.8 to have hang time for whole a second )
When a 10-kg falling object encounters 10 N of air resistance, its acceleration is
less than g
A piece of clay moving with one unit of kinetic energy strikes and sticks to a heavy bowling ball initially at rest. After the clay sticks, both ideally move with a combined kinetic energy of
less than one unit
Toss a ball straight upward, and each second on the way to the top it
loses 10 m/s in speed.
If an object has kinetic energy, it must also have
momentum
If the Earth's radius somehow shrunk, your weight on the shrunken surface would be
more (The idea of surface force increasing when a star shrinks leads to the huge forces near an ultimate shrunken star—a black hole)
A model airplane moves three times as fast as another identical model airplane. Compared with the kinetic energy of the slower airplane, the kinetic energy of the faster airplane is
more than four times as much
A model airplane moves three times as fast as another identical model airplane. Compared with the kinetic energy of the slower airplane, the kinetic energy of the faster airplane is
more than four times as much( k= 1/2 MV^2...its 9 times KE)
When an airplane flying horizontally in a straight line gains speed, the thrust on the plane is
more than the amount of air drag. (In gaining speed, the net force is greater than zero in the direction of the thrust, so thrust exceeds air drag. It is not in equilibrium.)
The equilibrium rule, F = 0, applies to
objects or systems at rest and objects or systems in uniform motion in a straight line. (We say objects moving with uniform motion in a straight line are not accelerating.)
Consider a space probe at a distance five times Earth's radius. Compared with gravitational force at Earth's surface, its gravitational attraction to Earth at this distance is about
one twenty-fifth as much.(Five times as far (inverse-square law) means 1/25 the gravitational attraction.)
Consider light from a candle. If you're five times as far away, its brightness will look about
one twenty-fifth as much.(Five times as far, according to the inverse-square law, is 1/25 the brightness)
On roller blades, you toss a ball horizontally away from you. The mass of the ball is one-tenth your mass. Compared with the speed you give to the ball, your recoil speed will ideally be
one-tenth as much.
When both the force and time of contact are doubled, the impulse on an object is
quadrupled.(2F 2t = 4Ft)
If the distance between two planets decreases to half, the force of gravity between them
quadruples (Twice as close means four times the force)
A car pulling a trailer accelerates when the gas pedal is pushed to the floor. If the trailer becomes disconnected, the acceleration of the car will
remain the same.(Newton's second law tells us that if the mass of something decreases while the force remains the same, then the acceleration will increase. The car minus the trailer has less mass.)
If the mass of an object decreases to half, and its speed doubles, its momentum
remains unchanged...m/2 2v = mv
Distance traveled is equal to average speed multiplied by
time, ( avg. speed = total distance traveled / travel time.... so total distance traveled = avg. speed X travel time
The force due to gravity on a body is the body
weight
