Physics Chapter 4 Test

What are two Scenarios Illustrating Newton's Second Law?

1. Ex 1: If two cars have same engine (i.e. same force propelling them), the object/car with greater mass will accelerate slower; thus, will require greater force to accelerate objects at same rate; if acceleration is equal, but one has larger mass, greater force/engine will be required to exert on larger car 2. Ex 2: If mass of cars is equal, and one is accelerating at faster rate than other, than greater force was exerted on the one accelerating at a faster rate

What is one approach to the Dice/Accelerometer Problem?

**NOTE: the forces of mg down and FT diagonal combined will cause the dice to accelerate

What is mass?

1. Newton's 2nd law makes use of concept of mass; 2. mass is amount of matter in something (intrinsic property); it is a measure of the inertia of an object 3. (thus, the more mass an object has, the greater the force needed to give it a particular acceleration; is harder to start it moving from rest, or to stop it when it's moving, or to change its velocity sideways out of a straight-line path-as exemplified by girl on horse)

What is a similar clarification to the cart application involving tension in a rope?

1. According to Newton's third law, each team in a tug of war pulls with equal force on the other team; what, then, determines which team will win? 2. Sol: In a tug of war, the team that pushes hardest against the ground wins. It is true that both teams have object is the same on both the Earth and the Moon, and both objects would have the same acceleration to throw them with the same speed. So by Newton's second law, the forces w have to be the same; the same force on them due to the tension in the rope. But the winning team pushes harder against the ground and thus the ground pushes harder on the winning team, making a net unbalanced force (similar to cart problem)

What is force?

1. Any kind of a push or a pull on an object (ex: when pushing grocery cart, you're exerting a force on it); an object is at rest, requires force to start it moving (i.e. force is needed to accelerate it from zero to nonzero velocity); 2. For object already moving, to change its velocity (either in direction or magnitude), force is required

What constitutes an Inertial Reference Frame?

1. Any reference frame that moves with constant velocity (ex: car or plane) relative to an inertial frame is an inertial reference frame and 2. mostly, we can assume that reference frames fixed on earth are inertial frames (not precisely true, but close enough); 3. thus, reference frame in which Newton's first law holds is an inertial ref. Frame, (inertial ref. Frame is a non accelerating ref. frame)

What are the Conventions of Force as a Vector Quantity?

1. As ever force, F, is a vector, with magnitude and acceleration, it can be written in component form in rectangular coordinates as: ΣFx = mas, ΣFy = may, ΣF = maz; 2. If the motion is all along a line (one-dimensional), we can leave out subscripts and simply write: ΣF = ma

How do Inanimate Objects Exert a Force?

1. Because every material is elastic, at least to some degree, 2. all materials stretch or compress when a force is applied to them, so, just as a stretched rubber band exerts a force, so does a stretched (or compressed) wall, desk, or car fender

What are the two reasons that indicate that Force is a Vector?

1. Because force involves direction (± depending on direction) 2. Because, since one component of force is acceleration, and "m" is a scalar, we know that "F" has to be a vector

What is Tension in a Flexible Cord?

1. Cords can pull, but can't push; 2. thus FT is always exerted upwards; 3. when a flexible cord pulls on an object, cord is under tension, and the force it exerts on object is the tension FT (if cord has negligible mass, force exerted at one end is transmitted undiminished to each adjacent piece of cord along entire length to other end-ex: if two boxes are attached by cord, FP exerted on one will translate into FT for other); 4. thus, forces pulling on cord at two ends must add up to zero (FT and -FT); flexible cords can only pull, NOT push

What is the Step-by-Step Process of Solving Newton's Laws Problems With Free-Body Diagrams?

1. Draw a sketch of the given situation; 2. Consider only one object at a time, and draw a free-body diagram for that object (showing ALL the force that you have to solve for-all forces acting on the object); don't show any forces that the chosen object exerts on other objects 3. Draw an arrow for each force vector reasonably accurately for direction and magnitude, labeling each force as to its source (Ex: gravity, mg, person, FA, normal force FN, friction, Ffr) 4. **If several objects are involved, draw free-body diagram for each object separately, showing only forces acting ON the given object-only forces acting ON object can be included in ΣF = ma for that particular object 5. Since Newton's 2nd law involves vectors, if necessary, resolve all vectors into their components; *choose one coordinate axis to be in direction of the acceleration (i.e. if object is accelerating downwards, convention is ΣF = ma = mg - FN ... etc, because mg has to be larger than FN or FT, because the object is accelerating downwards, and if object is accelerating upwards, when ΣF = ma = 0 = FN - mg, because mg has to be smaller than FN or FT); ** NOTE, when ma = 0, mg is negative, and thus convention will be FN - mg or FT - mg) 6. For each object, write down Newton's 2nd law to the x and y component of the forces separately; (i.e. the x component of net force on that object is ΣFx = mxa = ... and similarly for "y" direction; if object is not accelerating in a particular direction, then ΣF = ma = 0 = ... for that component, and if it is accelerating, plug in value for "m" or "a"; **NOTE: if object is moving at CONSTANT velocity, this corresponds to ma = 0) 7. Solve the equation for equation for the unknown(s); if there are two unknowns (Ex: if both FT and "a" are unknown-usually encountered when dealing with two objects-see if you can add/subtract one equation from other or isolate FT or FN and substitute one equation into the other to eliminate/cancel out on of unknowns

What is an Example Involving Apparent Weight in an Elevator?

1. Ex: A 65-kg woman descends in an elevator that briefly accelerates at 0.2 g downward when leaving a floor. She stands on a scale that reads in kg (a) During this acceleration, what is her weight and what does the scale read? (b) What does the scale read when the elevator descends at a constant speed of 2.0 m/s2? A. Sol: Draw free-body diagram; since if we take acceleration downwards as positive (mg) will be positive, and it must be larger than FN, because elevator is accelerating downwards, we write down NEwton's 2nd law using given acceleration (now, ΣF = ma does not = 0 because there is acceleration): ΣF = ma = mg - FN (Note: mg is pos. B. Because it has to be larger than FN); FN = mg - 0.2mg; FN = 0.8mg; how to find what the scale reads (her apparent mass), we divide FN by "g", because Force/acceleration = mass: ).8mg/g = 0.8m = (0.8)(65 kg) = 52 kg; weight stays same, mg, which is (65 kg)(9.8 m/s2) = 640 N Because the elevator descends at constant speed, this means that there is NO acceleration, and thus, it is as if ΣF = ma = 0 = mg - FN, so FN = mg, or simply the scale reads her true mass of 65 kg **NOTE: if given problem that says "scale reads 0.75 of mass," and asked to find acceleration of system, simply FN = 0.75mg, so since mg - FN = ma, m cancels out, so g - 0.75g = a **NOTE: only time FN changes is if there is acceleration

What is an Example of Newton's Laws Involving Car Collision?

1. Ex: A massive truck collides head-on with a small sports car. (a) Which vehicle experiences the greater force of impact? (b) Which experiences the greater acceleration? 2. Answer: (a) they both experience same force of impact (Newton's third law) (b) the smaller car experiences greater acceleration, because, since they both experience same force, and truck's mass is large, "a" of small car must be large to compensate (Newton's 2nd law)

What is a Conceptual Example Involving Inertial Reference Frames

1. Ex: A school bus comes to a sudden stop. And all of the backpacks on floor start to slide forward. What force causes them to do that? 2. Answer: It actually isn't a "force" that does it; the backpacks continued their motion, maintaining constant velocity (friction may slow them down), as the velocity of the bus decreases

Conceptual Example Involving Zero Acceleration and Zero Velocity

1. Ex: If only one force acts on an object, can the object have zero acceleration? Can it have zero velocity? Explain. 2. (a) If only once force acts on the object, then the net force cannot be zero. Thus the object cannot have zero acceleration, by Newton's second law. (b) The object can have zero velocity for an instant. For example, an object thrown straight up under the influence of gravity has a velocity of zero at the top of its path, but has a non-zero net force and non-zero acceleration throughout the entire flight.

Conceptual Example Involving Force of Tension in Pulled String

1. Ex: If stone hangs by thread from ceiling, as such: if person gives sharp pull on thread, where is thread likely to break: below stone or above it? What if the person gives a slow and steady pull? 2. Sol: (a) When giving a sharp pull, the key is the suddenness of the application of the force. When a large, sudden force is applied to the bottom string, the bottom string will have a large tension in it. Because of the stone's inertia, the upper string does not immediately experience the large force. The bottom string must have more tension in it, and will break first. (b) If a slow and steady pull is applied, the tension in the bottom string increases. We approximate that condition as considering the stone to be in equilibrium until the string breaks. The free-body diagram for the stone would look like this diagram. While the stone is in equilibrium, Newton's 2nd law states that F Fup = down + mg. Thus the tension in the upper string is going to be larger than the tension in the lower string because of the weight of the stone, and so the upper string will break first.

What is the Newton's Third Law Clarification With Person and Cart?

1. Ex: Person says, "When moving cargo using a sled, when I exert a force on the sled, the sled exerts an equal and opposite force backward. So how can I ever start it moving? No matter how hard I pull, the backward reaction force always equals my forward force." What is the problem with this statement? 2. Answer: While it is true that the action and reaction forces are equal in magnitude, the person has forgotten that they are exerted on different objects; the forward action is exerted by the assistant on the sled, whereas the backward "reaction" force is exerted by the sled on the person; **to determine whether the person moves or not, we must consider only the forces on the person. Amd then apply ΣF = ma, where ΣF is the net force on the person (the two forces on him that affect his forward motion are the horizontal force exerted on the person by the ground, and force exerted by sled on person; thus, if he pushes hard enough on ground, force exerted forward on him by ground will be larger than sled pulling back-if force exerted on him by ground is larger in magnitude than force exerted on him by cart, then he will move forward):

What is an Example Involving Using Constant Acceleration Equations With Newton's Second Law?

1. Ex: What average net force is required to bring a 1500-kg car to rest from a speed of 100 km/h within a distance of 55 m? 2. Sol: We can use Newton's second law, ΣF = ma, to determine the force iuf we know the mass and acceleration of the car; since we are not given acceleration, we can use constant acceleration equation to find it: since v0 = 100 km/h = 28 m/s, and v = 0; v2 = v02 + 2a(x - x0), (0)2 = (28 m/s)2 + 2a(55 m); a = -7.1 m/s2; then since ΣF = ma = (1500 kg)(-7.1 m/s2) = -1.1*104 N; thus, force must be exerted in the direction opposite to the initial velocity (which is what the negative sign means); **Note: when we're assuming acceleration is constant, as in this case, we're determining an "average" acceleration and thus we determine an "average" net force

What is an Example of Newton's Third Law Involving Hand on Table?

1. Ex: When pushing against edge of desk, you hand's shape is distorted, clear evidence that a force is being exerted on it; 2. you can feel desk exerting force on your hand; the harder you push against desk, the harder the desk pushes back on your hand

What is an Example of Mass and Inertia of Truck vs. Baseball?

1. Ex: a truck has more inertia than baseball moving at same speed, and 2. thus, it requires much greater force to change the truck's velocity at the same rate as the ball's; the ruck therefore has much more mass

What is the Definition of Force in Newton's Second Law?

1. Newton's 2nd law related description of motion to the cause of motion: force; 2. thus, from Newton's second law. We can make precise definition of force, which is: "an action capable of accelerating an object"

What is an Example Involving Finding Friction and Acceleration Along Incline?

1. Ex: skier has begun descending 30° slope; assuming coefficient of kinetic friction is 0.10, calculate (a) her acceleration and (b) the speed she'll reach after 4 s A. Sol: We choose x axis along incline, with y-axis as perpendicular to the surface; drawing free-body diagram: forces acting on skier are gravity (pointing vertically downward, NOT perpendicular to slope, FN and Ffr); in order to attain vertical and horizontal components of gravity: FGx = mgsinθ and FGy = -mgcosθ; if we write Newton's 2nd law for x direction (NOTE: MUST TAKE mgsinθ into account when calculating this): ΣFx - max = mgsinθ - Ffr = mgsinθ - ukFN = max; if we write Newton's 2nd law of y direction (no vertical accel): ΣFy = may = FN -mgcosθ = may = 0; thus, solving for FN, we know: FN = mgcosθ; since we have two unknowns and are trying to find "a," we can cancel out "m" by substituting "mgcosθ" for FN in ΣFx equation: since ΣFx = mgsinθ - ukFN = max, substituting for FN, we get: ΣFx = mgsinθ - uk(mgcosθ) = max. Since we know uk = 0.10, and θ = 30°: we can plug in: mgsin30° - 0.10(mg cos 30°) = max, cancel out "m," thus, a = 4.0 m/s2; it is often helpful to put #s in only at end, because we see that we can cancel out "m" B. To answer this, since we have accel, we can use constant accel equation: v = v0 + at to find speed after 4 s: v = 0 + (4m/s2)(4 s) = 16 m/s)

What are Examples of Newton's First Law/Law of Inertia

1. Ex: when you're standing on subway car and it stops suddenly, 2. you'll fall forward, because you were traveling at same speed as subway car, and due to your inertia, (tendency by object to keep doing what it's doing unless acted upon by unbalanced force), you move forward as car stops

What must be be careful of for Forces on Objects in Newton's Third Law?

1. For each force, be clear ON which object it acts, and BY which object it is exerted (ΣF = ma applies only to forces acting ON an object); 2. a force influences the motion of an object only when it's applied ON that object, whereas a force exerted BY an object does not influence that same object (it only influences the other object ON which it is exerted)

What is Static Friction?

1. Friction acting on a "stationary" object; refers to a force parallel to the two surfaces that can arise even when they aren't sliding (ex: if a desk is resting on ground, if there is no horizontal force exerted on it, there is no friction force; if you try to push the desk, it doesn't move, so there must be another force on the desk keeping it from moving-the net force is zero on an object that doesn't move-this is the force of static friction exerted by the floor on the desk; 2. If you push with greater force without moving the desk, the force of static friction has also increased. If you push hard enough, desk will eventually move, and kinetic friction takes over; at this point, you have exceeded the max. Force of static friction)

What is Kinetic Friction?

1. Friction acting on moving object/sliding friction; when object slides along rough surface, force of kinetic friction acts opposite to direction of object's velocity; magnitude of force KF depends on type of two sliding surfaces; 2. For given surfaces, the friction force is approx. proportional to the normal force between two surfaces (force that either object exerts on the other perpendicular to their common surface of contact)

What was Galileo's Hypothesis on Motion (basis for Newton's Law of Intertia)?

1. Galileo imagined idealized world (absence of friction), leading him to conclusion that if no force is applied to moving object, it will continue to move with constant speed in straight line, 2. and that object slows down only if force is exerted on it (he interpreted friction as force akin to ordinary pushes and pulls)

How do we identify a net force?

1. If net force is exerted on object, object's velocity will change; 2. net force exerted on an object may make its velocity increase, or if net force is exerted in direction opposite to motion, force will reduce object's velocity; if net force acts sideways on moving object, direction of object's vel. Changes; 3. Thus, since change in velocity corresponds to acceleration, we say that a net force causes acceleration

What is an Example of Newton's Third Law Involving Ice Skater?

1. If skater pushes against wall, she starts moving backwards, 2. which is testament to fact that something had to exert a force on her to start her moving (exerted by the wall); 3. the force with which the wall pushes on her is equal and opposite to the force she exerts on the wall (by Newton's third Law)

What is a Conceptual Question on Friction?

1. If ukFN were greater than FPx, what would you conclude? 2. Answer: The force applied by the person is insufficient to keep the box moving

What are the Units Used for Weight?

1. In SI units, g = 9.80 m/s2 = 9.80 N/kg, so the weight of a 1.00-kg mass on earth is 1.00 kg*9.80 m/s2 = 9.80 N; 2. we will be mainly concerned with the weight of objects on earth, but on other planets, or in space, the weight of a given mass will be different than it is on earth

What is Newton's First Law of Motion/Law of Inertia

1. Isaac Newton built upon Galileo's theory of motion, as summarized in his three laws of motion, the first of which states: 2. every object continues in its state of rest, or of uniform velocity in a straight line, as long as no net force acts on it

What are intertial ref. frames in the context of Newton's Second Law?

1. Newton's 2nd law, like the first, is only valid in inertial reference frames 2. (ex: in the noninertial ref. Frame of an accelerating car, a cup on dashboard accelerates, even though the net force on it is zero; thus ΣF = ma doesn't work in such an accelerating reference frame)

What are Inertial Reference Frames?

1. Newton's law doesn't hold in every reference frame (ex: if reference frame is fixed in an accelerating car, an object such as cup may move toward you-it stayed at rest as long as the velocity remained constant-while cup accelerated toward you, neither you nor anything else exerted force on it in that direction); 2. Similarly, if car stops an you move forward, no "force" is pushing you forward; thus, in accelerating reference frames, Newton's first law doesn't hold

What happens when we push an object across a table at a constant speed?

1. Pushing object across table requires force from hand that can balance out force of friction; 2. when object moves at constant speed, pushing force is equal in magnitude to the friction force, but these two forces are in opposite directions, so the net force on the object (vector sum of the two forces) is zero 3. Thus, object moves with constant speed when no net force is exerted on it (when there's no acceleration, there's no net force on the object)

How do we develop Newton's first law?

1. Pushing object with rough surface along tabletop at constant speed requires certain amount of force, and pushing equally heavy object with smooth surface at constant speed will require less force; 2. If lubricant placed between surfaces, then almost no force is required to move object (in case of perfect lubricant, object would move across table)

What is a Non-Inertial Reference Frame?

1. Reference frames where the law of inertia doesn't hold (i.e. accelerating reference frames) are called non-inertial reference frames 2. We can determine whether a reference frame is accelerating or not by checking to see if Newton's first law holds; thus. Law of Inertia serves as definition of inertial ref. frames)

What is an Example of Newton's Third Law with Rocket Repulsion?

1. Rockets accelerate because rocket exerts strong force on the gases, expelling them, and gases exert equal and opposite force on the rocket, which propels the rocket forward; 2. thus, space vehicle is maneuvered in empty space by firing its rockets in the direction opposite to that which it needs to accelerate (does NOT accelerate as result of its propelling gases pushing against ground)

What is the Weight of an Object?

1. Since gravitational force, FG, of an object, can be written as: FG = mg (where direction of this force is down towards center of earth), 2. the magnitude of the force of gravity of an object is commonly called the object's weight ( weight = gravitational force)

What is Newton's Second Law of Motion?

1. The acceleration of an object if directly proportional to the net force, ΣF, or Fnet, acting on it, 2. and is inversely proportional to its mass. 3. The direction of the acceleration is in the direction of the net force acting on the object.

What is the Proportionality Between Force, Acceleration, and Mass?

1. The acceleration of an object is directly proportional to the net applied force; However, acceleration of object depends on mass as well (ex: if you push empty cart with same force as you push filled on, full cart accelerated more slowly) 2. Thus, the greater the mass, the less corresponding acceleration for same net force (acceleration of object is inversely proportional to its mass)

What is weight?

1. The force of gravity, which is dependent on gravitational field, whose magnitude is "mg"; 2. **a scale measures the normal force, FN, not the weight of an object (commonly FN is equal to weight, but not always, as in apparent weight); 3. When object is accelerating downwards, FN is less than weight (FN = mg - ma), and when accelerating upwards, FN is greater than weight (FN = mg + ma)

What is the Forces of Gravity/Gravitational Acceleration?

1. The force that causes all objects dropped near surface of earth to accelerate at same rate is force of gravity; 2. the earth exerts the gravitational force on the object, acting vertically downward

How do the forces FN and FG Act on an Object at Rest?

1. The two forces shown are acting on the box, which remains at rest, so the vector sum of these two forces must be zero (second law); 2.**hence, FG and FN must be of equal magnitude and in opposite directions, *but they are NOT the equal and opp. Forces spoken of in Newton's 3rd law, because in this scenario, FN and FG act of SAME object, whereas the paired forces in Newton's 3rd law act on diff. Objects; 3. thus, force of gravity downward on box and force of floor upward on box are not on each other, they are on the box

What are the Paired Action-Reaction Forces of FN and FG (Newton's Third Law Forces)?

1. Upward force, FN, on box is exerted by table, and the paired force, or reaction to this is a force exerted by the box downward on the table, labeled FN (Newton's 3rd Law force) 2. The Newton's 3rd Law force action-reaction pair in terms of gravity FG downwards on box is the acceleration of the earth towards the box:

What is the Friction Proportionality Equation for Kinetic Friction?

1. We can write the proportionality between the friction force Ffr and the normal force FN as an equation by inserting a constant of proportionality, uk: Ffr = ukFN; where uk is the "coefficient of kinetic friction," which is dependent on the two types of surfaces involved; 2. FN acts perpendicular to the surfaces

What is Normal Force?

1. When a contact force acts perpendicular to the common surface of contact, it is referred to as the formal force, as labeled FN; 2. ** Weight and normal force are NOT action-reaction pairs; while commonly FN is equal to weight, it's not always equal to weight; thus*A SCALE READING MEASURES FN, THE NORMAL FORCE, NOT THE WEIGHT

What is the Force of Gravity on Objects at Rest?

1. When an object is at rest, the gravitational force on it does not disappear; 2. while the same force continues to act, from Newton's 2nd Law, the net force on an object that remains at rest is zero; 3. additionally, for an object resting on a table, there must be another force in the object to balance the gravitational force

What are Inclines and Friction?

1. When an object slides down an incline. Such as a hill or ramp, while gravity is the accelerating force, the acceleration is non vertical (acceleration is always between zero and 9.8 m/s2); 2. solving problems is usually easier if we choose the xy coordinate system so the x axis points along the incline and the y axis is perpendicular to the incline 3. (NOTE: this is because normal force is not vertical, but perpendicular to the sloping surface of the plane):

What is a Free-Body Diagram/Force Diagram?

1. When solving problems involving Newton's laws and force, one must draw a diagram showing all the forces acting ON each object involved; such a diagram is called a free-body, or force diagram 2. Choose one object, draw an arrow to represent each force acting on it (*INCLUDE EVERY FORCE ACTING ON THE OBJECT, BUT DO NOT SHOW FORCE THAT THE CHOSEN OBJECT EXERTS ON OTHER OBJECTS); to help identify these, ask yourself what other objects could exert a force on it; 3. If problem involves more than one object, draw separate free-body diagram for each object

What is Newton's Third Law?

1. Whenever one object exerts a force on second object, the second object exerts an equal force in the opposite direction on the first; 2. two objects must be involved; 3. while law is commonly referred to as "for every action there is an equal and opposite reaction," we must remember that the "action" force and the "reaction" force are acting on different objects; two objects must be involved

What is the Difference Between Mass and Weight?

1. While mass is a property of an object itself (a measure of an object's inertia. Or it's quantity of matter), 2. weight is a force, the pull of gravity acting on an object

Conceptual Example Involving Non-Inertial Reference Frames

1. ex: If a box rests on the (frictionless) bed of a truck, and when the truck accelerates forward, the box slides to the rear of the truck, discuss the motion of the box, in terms of Newton's laws, as seen by (a) person who is standing on ground beside truck and (b) person who's riding on the truck Sol: (a) Person on ground sees the box stay stationary with respect to the ground. There is no horizontal force on the box since the truck bed is smooth, and so the box cannot accelerate. Thus person would describe the motion of the box in terms of Newton's 1st law - there is no force on the box, so it does not accelerate. (b) Person riding truck from his non-inertial reference frame, would say something about the box being "thrown" backwards in the truck, and perhaps use Newton's 2nd law to describe the effects of that force. But the source of that force would be impossible to specify.

What are diagrams of force?

A force exerted in different directions has different effect; force has direction and magnitude (thus it is vetor that follows rules of vector addition); force can be representing in diagram by arrow, where direction of arrow is direction of push or pull, with its length drawn proportional to the magnitude of force

What is an Example of Newton's Third Law with Walking?

A person begins walking by pushing with the foot backward against the ground, and ground then exerts force forward on the person, and it is this force, on the person, that moves the person forward

What is Rolling Friction?

Even when a round object rolls across surface, there is till some friction, called rolling friction, although it's much less than when an object slides across a surface

What is an Example Involving Difference Between Mass and Weight?

An object will weigh only ⅙ as much on the moon as it will on earth, since force of gravity is weaker, but mass will be the same; it will have same amount of matter as on earth, and will have just as much inertia

What are the Paired Forces Acting on Free-Falling Object?

Ex: when releasing a ball, the earth is pulling the ball, but the ball is pulling the earth up, thus 9.8 N both ways; gravity is the only force not in physical contact with the object; every other force is in physical contact with it

How do we develop the Relationship Between Acceleration and Force?

Ex: when you push cart with gentle but constant force for long period of time, you'll make cart accelerate from rest up to some speed (ex: 3 km/h); if you push with twice force, cart will reach 3 km/h in halt the time, and thus, acceleration will be twice as great, if force is tripled, accel, with be tripled, etc.

How do we apply Newton's Second Law to an Object Falling Due to Gravity?

For an object of mass "m," for the acceleration "a," due to gravity, we use downward acceleration due to gravity, :g," thus, gravitational force on the object, "FG," can be written as: FG = mg

Does friction relate to surface area?

Force of friction between hard surfaces depends very LITTLE on total surface area of contact; in a simple model of friction, we make the assumption that the friction force is independent of area

What is a kilogram?

In SI units, the unit of mass is the kilogram (kg)

What is Net Force?

Newton's second law indicates that the acceleration of an object is proportional to the net force acting on the object; the net force is the vector sum of all forces acting on the object

How do we Measure Force Using a Spring Scale

One way to measure magnitude (or strength) of force is to use spring scale; normally, is used to find the weight of an object (i.e. The force of gravity acting on the object), but it can also be used to measure pulling force)

What is net force?

Since Σ means "sum of," ΣF means "the vector sum of all forces" acting on an object, which we define as the net force

What is the Magnitude of Static Friction vs. Kinetic Friction?

Static friction is larger than kinetic friction because it requires more force to start an object moving than it does to simply keep it in motion (due to electrostatic attraction that holds object in place); this is consistent with us generally being greater than uk

What is Electrostatic Attraction and Friction?

The atoms on the bump of one surface come so close to the atoms of another surface that attractive electric forces between the atoms can "bond" as a tiny weld between the two surfaces; sliding an object across surface is jerky due to making and breaking of bonds

What is inertia?

The tendency of an object to maintain its states of rest or of uniform motion in a straight line is called inertia

What Makes a Car Go Forward?

While common answer is that the engine makes it go forward, it is not so simple; friction is needed; on solid ground, tires push backward against the ground because of friction, and by Newton's third law, the ground pushes on the tires in the opposite direction, accelerating the car forward

What is the Hammer and Nail Example of Newton's Third Law?

While hammer exerts force on nail, the nail exerts a force on the hammer as well (because the hammer's speed is rapidly reduced to zero upon contact) and only a strong force could cause such rapid deceleration of the hammer