Chapter 12 Forces and Motion 12.1 Forces. A force is a push or a pull that acts on an object. It can cause a resting object to move, or it can accelerate

Chapter 12Chapter 12Forces and MotionForces and Motion

12.1 Forces12.1 Forces

A force is a push or a pull that acts on an object.

It can cause a resting object to move, or it can accelerate a moving object by changing the object’s speed or direction.

What Is a Force?

Units of Force

One newton (N) is the force that causes a 1-kilogram mass to accelerate at a rate of 1 meter per second each second (1 m/s2).

1 N = 1 kg•m/s2

When the forces on an object are balanced, the net force is zero

There is no change in the object’s motion.

Combining Forces

When an unbalanced force acts on an object, the object accelerates.

The The net forcenet force is the overall force is the overall force acting on an object after all the acting on an object after all the forces are combined.forces are combined.

• Forces in the same direction Forces in the same direction add together.add together.

• Forces in opposite directions Forces in opposite directions subtract from one another.subtract from one another.

Balanced ForcesBalanced forcesBalanced forces are forces that are forces that combine to produce a net force of combine to produce a net force of zero. zero.

An unlimited number of individual An unlimited number of individual forces can act on an object to forces can act on an object to produce a net force of zero.produce a net force of zero.

Unbalanced Forces

An An unbalanced forceunbalanced force is a is a force that results when force that results when the net force acting on an the net force acting on an object is not equal to object is not equal to zero.zero.

Activity CalculatingActivity CalculatingTugboat A exerts a force of 4000 N Tugboat A exerts a force of 4000 N

on a barge. Tugboat B exerts a force on a barge. Tugboat B exerts a force of 8000 N on the barge in the same of 8000 N on the barge in the same direction. What is the combined direction. What is the combined force? Using arrows draw the force? Using arrows draw the combined forces. Then draw the combined forces. Then draw the forces involved if the tugboats were forces involved if the tugboats were pulling in opposite directions.pulling in opposite directions.

ANSWER:ANSWER:

In the same direction:In the same direction:

4000N + 8000N = 12000N4000N + 8000N = 12000N

In opposite directions:In opposite directions:

4000N – 8000N = 4000N toward the 4000N – 8000N = 4000N toward the direction of tugboat Bdirection of tugboat B

Friction is a force that opposes the motion of objects that touch as they move past each other.

Friction

four main types of friction: four main types of friction:

static frictionstatic friction

sliding frictionsliding friction

rolling frictionrolling friction

fluid friction. fluid friction.

Static Friction

Static frictionStatic friction is the friction is the friction force that acts on objects that force that acts on objects that are not moving. are not moving.

Static friction always acts in the Static friction always acts in the direction opposite to that of the direction opposite to that of the applied force.applied force.

Rolling Friction

Rolling frictionRolling friction is the friction is the friction force that acts on rolling force that acts on rolling objects. objects.

• about 100 to 1000 times less about 100 to 1000 times less than the force of static orthan the force of static or sliding friction.sliding friction.

Sliding FrictionSliding Friction

Sliding frictionSliding friction is a force that is a force that opposes the direction of motion opposes the direction of motion of an object as it slides over a of an object as it slides over a surface. surface.

Sliding friction is less than static Sliding friction is less than static friction.friction.

Fluid FrictionFluid Friction• Fluid frictionFluid friction opposes the motion of opposes the motion of

an object through a fluid.an object through a fluid.• increases as the speed of the increases as the speed of the

object moving through the fluid object moving through the fluid increases.increases.

• Fluid friction acting on an object Fluid friction acting on an object moving through the air is known as moving through the air is known as air resistanceair resistance. .

Gravity

Earth’s gravity acts downward toward the center of Earth.

How do gravity and air resistance affect a falling object?

Gravity causes objects to accelerate downward, whereas air resistance acts in the direction opposite to the motion and reduces acceleration.

GravityGravity is a force that acts is a force that acts between any two masses. between any two masses.

• an attractive force. an attractive force. • can act over large can act over large distances.distances.

Free FallFree FallFree fallFree fall – motion of an – motion of an

object when gravity is the object when gravity is the only force acting on itonly force acting on it

All objects near earth All objects near earth accelerate at 9.8 m/saccelerate at 9.8 m/s2 2 in in the absence of air the absence of air resistanceresistance

Terminal VelocityTerminal VelocityTerminal VelocityTerminal Velocity – –

when air resistance when air resistance balances weight and the balances weight and the object stops accelerating object stops accelerating and reaches its and reaches its maximum velocitymaximum velocity320 km/h (200 mi/h) 320 km/h (200 mi/h)

A thrown ball follows a curved path. A thrown ball follows a curved path.

Projectile motionProjectile motion is the motion of a is the motion of a falling object (projectile) after it is falling object (projectile) after it is given an initial forward velocity. given an initial forward velocity.

Air resistance and gravity are Air resistance and gravity are the only forces acting on a the only forces acting on a projectile.projectile.

Projectile Motion

REVIEW1.1. If an object is at rest, which of the If an object is at rest, which of the

following statements must be true? following statements must be true?

a.a. There are no forces acting on the There are no forces acting on the object.object.

b.b. There is no friction acting on the There is no friction acting on the object.object.

c.c. The forces acting on the object are The forces acting on the object are unbalanced.unbalanced.

d.d. The net force acting on the object is The net force acting on the object is zero.zero.

REVIEW1.1. If an object is at rest, which of the If an object is at rest, which of the

following statements must be true? following statements must be true?

a.a. There are no forces acting on the There are no forces acting on the object.object.

b.b. There is no friction acting on the There is no friction acting on the object.object.

c.c. The forces acting on the object are The forces acting on the object are unbalanced.unbalanced.

d.d. The net force acting on the object is The net force acting on the object is zero.zero.

2.2. Which of the following is not Which of the following is not a type of friction?a type of friction?a.a. static frictionstatic frictionb.b. sliding frictionsliding frictionc.c. fluid frictionfluid frictiond.d. pull frictionpull friction

REVIEW

2.2. Which of the following is not Which of the following is not a type of friction?a type of friction?a.a. static frictionstatic frictionb.b. sliding frictionsliding frictionc.c. fluid frictionfluid frictiond.d. pull frictionpull friction

REVIEW

3.3. In which direction does Earth’s In which direction does Earth’s gravitational force act? gravitational force act? a.a. opposite the direction of motionopposite the direction of motionb.b. downward toward the center of downward toward the center of

EarthEarthc.c. upward away from the center of upward away from the center of

EarthEarthd.d. in the direction of motionin the direction of motion

REVIEW

3.3. In which direction does Earth’s In which direction does Earth’s gravitational force act? gravitational force act? a.a. opposite the direction of motionopposite the direction of motionb.b. downward toward the center of downward toward the center of

EarthEarthc.c. upward away from the center of upward away from the center of

EarthEarthd.d. in the direction of motionin the direction of motion

REVIEW

4.4. A ball thrown into the air follows a A ball thrown into the air follows a projectile course due to the initial projectile course due to the initial velocity and thevelocity and the

a.a. force of gravity.force of gravity.

b.b. effect of air resistance.effect of air resistance.

c.c. motion of Earth beneath it.motion of Earth beneath it.

d.d. mass of the ball.mass of the ball.

REVIEW

4.4. A ball thrown into the air follows a A ball thrown into the air follows a projectile course due to the initial projectile course due to the initial velocity and thevelocity and the

a.a. force of gravityforce of gravity..

b.b. effect of air resistance.effect of air resistance.

c.c. motion of Earth beneath it.motion of Earth beneath it.

d.d. mass of the ball.mass of the ball.

REVIEW

5.5. The SI unit for force is 1 The SI unit for force is 1 kg•m/skg•m/s22, also called one , also called one kepler. kepler.

TrueTrueFalseFalse

REVIEW

5.5. The SI unit for force is 1 The SI unit for force is 1 kg•m/skg•m/s22, also called one , also called one kepler. kepler.

False: The SI unit for force is False: The SI unit for force is 1 kg•m/s1 kg•m/s22, also called one , also called one Newton.Newton.

REVIEW


12.2 Newton’s first and 12.2 Newton’s first and second laws of motionsecond laws of motion

Newton

Newton built on the work of Newton built on the work of scientists such as Galileo. scientists such as Galileo.

• Newton first defined mass Newton first defined mass and force.and force.

• He then introduced his He then introduced his laws of motion.laws of motion.

Newton’s First Law of MotionAccording to Newton’s first law of motion, the state of motion of an object does not change as long as the net force acting on the object is zero.

Unless acted upon by an Unless acted upon by an unbalanced force, an object at rest unbalanced force, an object at rest remains at rest and an object in remains at rest and an object in motion remains in motion with the motion remains in motion with the same speed and direction.same speed and direction.

InertiaInertia is the tendency of an object is the tendency of an object to resist a change in its motion.to resist a change in its motion.

Newton’s Second Law of Motion

Newton’s second law of motion: the acceleration of an object is equal to the net force acting on it divided by the object’s mass.

The acceleration of an object is directly The acceleration of an object is directly proportional to the net force acting on proportional to the net force acting on it. it.

also depends upon its mass. also depends upon its mass. Mass is a measure of the inertia of Mass is a measure of the inertia of

an object.an object.

Newton’s Second Law of Motion F = ma

22ndnd Law Example Law Example

How much force is needed to How much force is needed to accelerate a 1400 kg car 2 m/saccelerate a 1400 kg car 2 m/s22??

22ndnd Law Example Law Example

How much force is needed to How much force is needed to accelerate a 1400 kg car 2 m/saccelerate a 1400 kg car 2 m/s22??

F = 1400kg x 2 m/sF = 1400kg x 2 m/s22

F = 2800NF = 2800N

(Remember: 1 N = 1 kg•m/s2 ))

F = ma

Newton’s Second LawNewton’s Second Law

An automobile with a mass of An automobile with a mass of 1000 kilograms accelerates 1000 kilograms accelerates when the traffic light turns when the traffic light turns green. If the net force on the car green. If the net force on the car is 4000 newtons, what is the is 4000 newtons, what is the car’s acceleration?car’s acceleration?

Newton’s Second LawNewton’s Second Law

F = ma4000N = 1000kg x m/s2

4000 / 1000 = 4 m/s2

Acceleration = 4 m/s2

1.1. A boy pushes forward a cart A boy pushes forward a cart of groceries with a total mass of groceries with a total mass of 40.0 kg. What is the of 40.0 kg. What is the acceleration of the cart if the acceleration of the cart if the net force on the cart is 60.0 N? net force on the cart is 60.0 N?


1.1. A boy pushes forward a cart of A boy pushes forward a cart of groceries with a total mass of 40.0 kg. groceries with a total mass of 40.0 kg. What is the acceleration of the cart if What is the acceleration of the cart if the net force on the cart is 60.0 N?the net force on the cart is 60.0 N?

F = maF = ma

60 = 40kg x m/s60 = 40kg x m/s22

60 / 40 = 4.5 m/s60 / 40 = 4.5 m/s22

acceleration = 4.5 m/sacceleration = 4.5 m/s22


22ndnd Law Practice Law Practice1.1. How much force is needed to How much force is needed to

accelerate a 66 kg skier 1 m/saccelerate a 66 kg skier 1 m/s22??

2.2. What is the force on a 1000 kg What is the force on a 1000 kg elevator that is falling freely at 9.8 elevator that is falling freely at 9.8 m/sm/s22??

3.3. A baseball accelerates down at 9.8 A baseball accelerates down at 9.8 m/sm/s22. If the force is 1.4 N, what is the . If the force is 1.4 N, what is the baseball’s mass?baseball’s mass?

22ndnd Law Practice Law Practice

1.1. How much force is needed to accelerate a 66 kg How much force is needed to accelerate a 66 kg skier 1 m/sskier 1 m/s22??

66N66N2. What is the force on a 1000 kg elevator that is falling 2. What is the force on a 1000 kg elevator that is falling

freely at 9.8 m/sfreely at 9.8 m/s22??

9800 N9800 N3. A baseball accelerates down at 9.8 m/s3. A baseball accelerates down at 9.8 m/s22. If the force . If the force

is 1.4 N, what is the baseball’s mass?is 1.4 N, what is the baseball’s mass?

0.143kg 0.143kg

Mass and weight are related but are Mass and weight are related but are notnot the same. the same.

• Mass is the measure of the Mass is the measure of the amount of material an object amount of material an object contains. contains.

• Weight is the force of gravity Weight is the force of gravity acting on an object. acting on an object.

• Weight is the product mass and Weight is the product mass and acceleration due to gravity.acceleration due to gravity.

W W == mg mg is a different form of is a different form of Newton’s Second Law, Newton’s Second Law, F = ma.F = ma.

The value of The value of g g in the formula is in the formula is 9.8 m/s9.8 m/s22..

Weight and Mass

If an astronaut has a mass of 112 If an astronaut has a mass of 112 kilograms, what is his weight on Earth kilograms, what is his weight on Earth where the acceleration due to gravity is where the acceleration due to gravity is 9.8 m/s9.8 m/s22??

Weight and Mass

If an astronaut has a mass of 112 If an astronaut has a mass of 112 kilograms, what is his weight on Earth kilograms, what is his weight on Earth where the acceleration due to gravity is where the acceleration due to gravity is 9.8 m/s9.8 m/s22??

Weight = 112 kg x 9.8 m/sWeight = 112 kg x 9.8 m/s22

Weight = 1097.6 NWeight = 1097.6 N

Weight and Mass

Weight CalculationsWeight Calculations

1.1. A 10 kg mass would weigh __A 10 kg mass would weigh __2.2. A 50 kg mass would weigh __A 50 kg mass would weigh __3.3. A 100 kg mass would weigh __A 100 kg mass would weigh __

Weight CalculationsWeight Calculations

1.1. A 10 kg mass would weigh A 10 kg mass would weigh __98 N98 N__2.2. A 50 kg mass would weigh A 50 kg mass would weigh __490 N490 N__3.3. A 100 kg mass would weigh A 100 kg mass would weigh __980 N980 N__

REVIEW

1.1. What is inertia? What is inertia?

a.a. the force of gravity acting on an objectthe force of gravity acting on an object

b.b. forces of friction slowing an object’s forces of friction slowing an object’s motionmotion

c.c. the mass of an objectthe mass of an object

d.d. the tendency of an object to resist the tendency of an object to resist change in its motionchange in its motion

REVIEW

1.1. What is inertia? What is inertia?

a.a. the force of gravity acting on an objectthe force of gravity acting on an object

b.b. forces of friction slowing an object’s forces of friction slowing an object’s motionmotion

c.c. the mass of an objectthe mass of an object

d.d. the tendency of an object to resist the tendency of an object to resist change in its motionchange in its motion

REVIEW

2.2. A 3600-N force causes a car to A 3600-N force causes a car to accelerate at a rate of 4 m/saccelerate at a rate of 4 m/s22. What . What is the mass of the car? is the mass of the car? a.a. 600 kg600 kgb.b. 900 kg900 kgc.c. 14,400 kg14,400 kgd.d. 1200 kg1200 kg

REVIEW

2.2. A 3600-N force causes a car to A 3600-N force causes a car to accelerate at a rate of 4 m/saccelerate at a rate of 4 m/s22. What . What is the mass of the car? is the mass of the car? a.a. 600 kg600 kgb.b. 900 kg = 3600 / 4900 kg = 3600 / 4c.c. 14,400 kg14,400 kgd.d. 1200 kg1200 kg

REVIEW

3.3. How would your mass and weight change if How would your mass and weight change if you were on the moon’s surface? you were on the moon’s surface?

a.a. They wouldn’t change.They wouldn’t change.

b.b. Your mass would remain constant, and your Your mass would remain constant, and your weight would increase.weight would increase.

c.c. Your mass and weight would decrease.Your mass and weight would decrease.

d.d. Your mass would remain constant, and your Your mass would remain constant, and your weight would decrease.weight would decrease.

REVIEW

3.3. How would your mass and weight change if How would your mass and weight change if you were on the moon’s surface? you were on the moon’s surface?

a.a. They wouldn’t change.They wouldn’t change.

b.b. Your mass would remain constant, and your Your mass would remain constant, and your weight would increase.weight would increase.

c.c. Your mass and weight would decrease.Your mass and weight would decrease.

d.d. Your mass would remain constant, and your Your mass would remain constant, and your weight would decrease. (Acceleration due to weight would decrease. (Acceleration due to gravity would be less on the moon)gravity would be less on the moon)


12.3 Newton’s Third Law of 12.3 Newton’s Third Law of Motion and MomentumMotion and Momentum

Newton’s Third Law

According to Newton’s third 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.

Momentum is the product of an object’s mass and its velocity.

Momentum

momentum is large if the product of its mass and velocity is large.

An object with large An object with large momentum is harder to momentum is harder to stop than an object with stop than an object with small momentum. small momentum. The momentum for any The momentum for any object at rest is zero.object at rest is zero.

Mass is measured in kilograms.Mass is measured in kilograms.

Velocity is measured in meters per Velocity is measured in meters per second.second.

Momentum is measured kilogram-Momentum is measured kilogram-meters per second.meters per second.

Momentum p = mv

MomentumMomentum

Unit: kgUnit: kg·m/s·m/s

Ex: Calculate the momentum of a Ex: Calculate the momentum of a 6.00 kg bowling ball moving at 6.00 kg bowling ball moving at 10.0 m/s down the alley10.0 m/s down the alley

MomentumMomentum

Unit: kgUnit: kg·m/s·m/s

Ex: Calculate the momentum of a Ex: Calculate the momentum of a 6.00 kg bowling ball moving at 10.0 6.00 kg bowling ball moving at 10.0 m/s down the alleym/s down the alley

pp = mv = mv

pp = 6 kg x 10 m/s = 6 kg x 10 m/s

60 kg60 kg·m/s = momentum·m/s = momentum

p = mv

Which has more momentum, Which has more momentum, a 0.046-kilogram golf ball a 0.046-kilogram golf ball with a speed of 60.0 meters with a speed of 60.0 meters per second, or a 7.0-kilogram per second, or a 7.0-kilogram bowling ball with a speed of bowling ball with a speed of 6.0 meters per second?6.0 meters per second?

Momentum

Which has more momentum, Which has more momentum, a 0.046-kilogram golf ball a 0.046-kilogram golf ball with a speed of 60.0 meters with a speed of 60.0 meters per second per second (2.76(2.76 kg kg·m/s)·m/s) , or , or a 7.0-kilogram a 7.0-kilogram bowling ball bowling ball with a speed of 6.0 meters with a speed of 6.0 meters per second per second (42(42 kg kg·m/s)·m/s)??

Momentum

Momentum PracticeMomentum Practice1.1. 75 kg speed skater moving 75 kg speed skater moving

forward at 16 m/sforward at 16 m/s2.2. 135 kg ostrich running north at 135 kg ostrich running north at

16.2 m/s16.2 m/s3.3. A 5.0 kg baby on a train moving A 5.0 kg baby on a train moving

east at 72 m/seast at 72 m/s4.4. 48.5 kg person on a stopped train48.5 kg person on a stopped train

Momentum PracticeMomentum Practice1. 75 kg speed skater moving forward at 16 m/s1. 75 kg speed skater moving forward at 16 m/s

75kg x 16m/s = 1200 kg75kg x 16m/s = 1200 kg·m/s·m/s2. 135 kg ostrich running north at 16.2 m/s2. 135 kg ostrich running north at 16.2 m/s

135kg x 16.2m/s = 2187 kg135kg x 16.2m/s = 2187 kg·m/s·m/s3. A 5.0 kg baby on a train moving east at 72 3. A 5.0 kg baby on a train moving east at 72

m/sm/s

5kg x 72m/s = 360 kg5kg x 72m/s = 360 kg·m/s·m/s4. 48.5 kg person on a stopped train4. 48.5 kg person on a stopped train

48.5kg x 0m/s = 0 kg48.5kg x 0m/s = 0 kg·m/s·m/s

A closed system means other objects and forces cannot enter or leave a system.

Conservation of Momentum

In a closed system, the loss of momentum of one object equals the gain in momentum of another object— momentum is conserved..

Objects within a closed system can Objects within a closed system can exert forces on one another.exert forces on one another.

Law of conservation of momentum:Law of conservation of momentum:

if no net force acts on a system, if no net force acts on a system, then the total momentum of the then the total momentum of the system does not change.system does not change.

Conservation of Momentum

REVIEW

1.1. A stationary figure skater pushes off the A stationary figure skater pushes off the boards around an ice skating rink and boards around an ice skating rink and begins gliding backward, away from the begins gliding backward, away from the boards. Which law explains why the boards. Which law explains why the figure skater moves backward? figure skater moves backward? a.a. the law of conservation of energythe law of conservation of energyb.b. the law of inertiathe law of inertiac.c. Newton’s second lawNewton’s second lawd.d. Newton’s third lawNewton’s third law

REVIEW

1.1. A stationary figure skater pushes off the A stationary figure skater pushes off the boards around an ice skating rink and boards around an ice skating rink and begins gliding backward, away from the begins gliding backward, away from the boards. Which law explains why the boards. Which law explains why the figure skater moves backward? figure skater moves backward? a.a. the law of conservation of energythe law of conservation of energyb.b. the law of inertiathe law of inertiac.c. Newton’s second lawNewton’s second lawd.d. Newton’s third lawNewton’s third law

Chapter 12Chapter 12

12.4 Universal Forces12.4 Universal Forces

Four universal forces exist Four universal forces exist throughout the universe. throughout the universe.

• electromagneticelectromagnetic• strong nuclearstrong nuclear• weak nuclearweak nuclear• gravitational gravitational

Electromagnetic Forces

Electric force and magnetic force are the only forces that can both attract and repel.

Electric and magnetic force Electric and magnetic force are two different aspects of are two different aspects of the electromagnetic force. the electromagnetic force.

Electromagnetic forceElectromagnetic force is is associated with charged associated with charged particles.particles.

Electromagnetic Forces

Electric ForcesElectric Forces

Electric forcesElectric forces act between act between charged objects or particles.charged objects or particles.

• Objects with opposite Objects with opposite charges attract one another. charges attract one another.

• Objects with like charges Objects with like charges repel one another. repel one another.

Magnetic ForcesMagnetic Forces

Magnetic forcesMagnetic forces act on act on• certain metals,certain metals,• the poles of magnets, the poles of magnets, andand

• moving charges. moving charges.

Magnets have two poles—Magnets have two poles—north and south.north and south.

• Two poles that are Two poles that are opposite attract each opposite attract each other.other.

• Two poles that are alike Two poles that are alike repel each other. repel each other.

Nuclear Forces

Two forces, the strong nuclear force and the weak nuclear force, act within the nucleus to hold it together.

The The strong nuclear forcestrong nuclear force overcomes the electric force of overcomes the electric force of repulsion that acts among the repulsion that acts among the protons in the nucleus. protons in the nucleus.

The The weak nuclear forceweak nuclear force is is involved in certain types of involved in certain types of radioactive processes.radioactive processes.

Nuclear Forces

Gravitational Forces

Newton’s law of universal gravitation states that every object in the universe attracts every other object.

Gravitational forceGravitational force is an attractive is an attractive force that acts force that acts between any two between any two masses.masses. -depends -depends upon upon

mass and mass and distance. distance.

Gravity Acts Over Long DistancesGravity Acts Over Long Distances

The gravitational force between two The gravitational force between two objects is proportional to their masses.objects is proportional to their masses.

decreases with the square of the decreases with the square of the distance between the objects. distance between the objects.

Gravity is the weakest universal force, Gravity is the weakest universal force, but it is the most effective force over but it is the most effective force over long distances. long distances.


The Earth, Moon, and TidesThe Earth, Moon, and Tides

Earth’s gravitational attraction keeps Earth’s gravitational attraction keeps the moon in a nearly circular orbit the moon in a nearly circular orbit around Earth. around Earth.

A A centripetal forcecentripetal force is a center-directed is a center-directed force that continuously changes the force that continuously changes the direction of an object to make it move in direction of an object to make it move in a circle. a circle.


REVIEW

1.1. What are the only forces that can What are the only forces that can both attract and repel? both attract and repel?

a.a. electromagnetic forceselectromagnetic forces

b.b. centripetal forcescentripetal forces

c.c. strong nuclear forcesstrong nuclear forces

d.d. gravitational forcesgravitational forces

REVIEW

1.1. What are the only forces that can What are the only forces that can both attract and repel? both attract and repel?

a.a. electromagnetic forceselectromagnetic forces

b.b. centripetal forcescentripetal forces

c.c. strong nuclear forcesstrong nuclear forces

d.d. gravitational forcesgravitational forces

2.2. The nucleus of an atom is held The nucleus of an atom is held together primarily by the together primarily by the a.a. strong force and weak force.strong force and weak force.b.b. strong force and gravity.strong force and gravity.c.c. weak force and electromagnetic weak force and electromagnetic

force.force.d.d. electromagnetic force and strong electromagnetic force and strong

force.force.

REVIEW

2.2. The nucleus of an atom is held The nucleus of an atom is held together primarily by the together primarily by the a.a. strong force and weak force.strong force and weak force.b.b. strong force and gravity.strong force and gravity.c.c. weak force and electromagnetic weak force and electromagnetic

force.force.d.d. electromagnetic force and strong electromagnetic force and strong

force.force.

REVIEW

3.3. Which of the following statements about Which of the following statements about gravitational forces is false? gravitational forces is false?

a.a. They are the weakest universal forces.They are the weakest universal forces.

b.b. They act between any two objects.They act between any two objects.

c.c. They become stronger as the distance They become stronger as the distance between two objects increases.between two objects increases.

d.d. They become weaker as the mass of They become weaker as the mass of either two objects decreases.either two objects decreases.

REVIEW

3.3. Which of the following statements about Which of the following statements about gravitational forces is gravitational forces is falsefalse? ?

a.a. They are the weakest universal forces.They are the weakest universal forces.

b.b. They act between any two objects.They act between any two objects.

c.c. They become stronger as the distance They become stronger as the distance between two objects increases.between two objects increases.

d.d. They become weaker as the mass of They become weaker as the mass of either two objects decreases.either two objects decreases.

REVIEW

4.4. A center-directed force that A center-directed force that continuously changes the direction of continuously changes the direction of an object’s motion, making it move in a an object’s motion, making it move in a circle, is called the radial force.circle, is called the radial force.

TrueTrueFalseFalse

REVIEW

4.4. A center-directed force that A center-directed force that continuously changes the direction of continuously changes the direction of an object’s motion, making it move in a an object’s motion, making it move in a circle, is called the radial force.circle, is called the radial force.

TrueTrueFalseFalse

REVIEW

Documents

Chapter 12 Forces and Motion 12.1 Forces. A force is a push or a pull that acts on an object. It can cause a resting object to move, or it can accelerate