GravityGravityNewton’s Laws of MotionNewton’s Laws of Motion

Chapter 5: Section 4Chapter 5: Section 4

Chapter 6: Section 2Chapter 6: Section 2

GravityGravity

A force of attraction between objects that A force of attraction between objects that is due to their masses. is due to their masses.

Because gravity is less on the moon

than on Earth, walking on the moon’s surface

was a very bouncy experience for the Apollo astronauts.

All Matter Is Affected by GravityAll Matter Is Affected by Gravity

All objects experience an attraction toward All objects experience an attraction toward all other objects.all other objects.

Because of gravity you are being pulled Because of gravity you are being pulled toward this book, your pencil, and every toward this book, your pencil, and every other object around you. Do you know other object around you. Do you know why?why?

Earth’s Gravitational Force Is LargeEarth’s Gravitational Force Is Large“It’s Truly Incomparable”“It’s Truly Incomparable”

Compared with “all” the objects around you, Compared with “all” the objects around you, Earth has a enormous mass.Earth has a enormous mass.

The Law of Universal GravitationThe Law of Universal Gravitation

Why do objects fall toward Earth?Why do objects fall toward Earth?What keeps the planets in motion in the What keeps the planets in motion in the

sky?sky?

Newton Makes the Connection

The Law of Universal Gravitation states that all The Law of Universal Gravitation states that all objects in the universe attract each other objects in the universe attract each other

through gravitational force. The size of the force through gravitational force. The size of the force depends on the masses of the object and the depends on the masses of the object and the

distance between them.distance between them.

For Example…For Example…

Gravitational force increases as Gravitational force increases as mass increases. mass increases.

Imagine an Elephant and a CatImagine an Elephant and a CatOr imagine the Earth and the MoonOr imagine the Earth and the Moon

Gravitational force decreases as distance Gravitational force decreases as distance increases.increases.Gravity between you and the EarthGravity between you and the EarthGravity between you and the SunGravity between you and the Sun

Weight and Mass are DifferentWeight and Mass are Different

Weight is a measure of the gravitational force Weight is a measure of the gravitational force exerted on an object.exerted on an object.

Do you know what that means?Do you know what that means?

Mass is the amount of matter “Stuff” in an object, Mass is the amount of matter “Stuff” in an object, and its value does not change.and its value does not change. If an object is moved to a place “Geographically If an object is moved to a place “Geographically

Speaking” with a greater gravitational force (Jupiter) Speaking” with a greater gravitational force (Jupiter) its weight will increase, but its mass will remain the its weight will increase, but its mass will remain the same. same.

Newton’s Laws of MotionNewton’s Laws of Motion

Newton’s First LawNewton’s First Law

An object at rest remains at rest and an An object at rest remains at rest and an object in motion remains in motion at object in motion remains in motion at constant speed and in a straight line constant speed and in a straight line unless acted on by an unbalanced force.unless acted on by an unbalanced force.

Objects at “Rest”… Let’s share some of Objects at “Rest”… Let’s share some of the many examples illustratively “Smile”the many examples illustratively “Smile”

Objects in Motion… Meaning ?Objects in Motion… Meaning ?

This law is also sometimes called the law of This law is also sometimes called the law of inertia. Why?inertia. Why?

Inertia is the tendency of all object to resist any Inertia is the tendency of all object to resist any change in motion.change in motion.

Mass is a measure of inertia.Mass is a measure of inertia.

Newton’s Second LawNewton’s Second Law

The acceleration of an object depends on The acceleration of an object depends on the mass of the object and the amount of the mass of the object and the amount of force applied.force applied.Acceleration depends on massAcceleration depends on massAcceleration depends on force Acceleration depends on force

If the force applied is the same, the acceleration of If the force applied is the same, the acceleration of the empty cart is greater than the acceleration of the empty cart is greater than the acceleration of

the full cart.the full cart.

Acceleration will increase when a larger Acceleration will increase when a larger force is exerted.force is exerted.

Newton’s Second Law and Newton’s Second Law and Acceleration are due to GravityAcceleration are due to Gravity

Newton’s Third LawNewton’s Third Law

Whenever one object exerts a force on a Whenever one object exerts a force on a second object, the second object exerts an second object, the second object exerts an equal and opposite force on the first.equal and opposite force on the first.

All forces act in pairs. What does this All forces act in pairs. What does this mean?mean?

Action and Reaction ForcesAction and Reaction Forces

““Momentum Anyone?”Momentum Anyone?”

Momentum is a property of a moving Momentum is a property of a moving object that depends on the object’s mass object that depends on the object’s mass and velocity.and velocity.

Momentum is Conserved. Just how is this Momentum is Conserved. Just how is this done?done?

The momentum before a collision is equal to The momentum before a collision is equal to the momentum after the collision.the momentum after the collision.

Conservation of Momentum and Newton’s Conservation of Momentum and Newton’s Third LawThird Law

For Review…For Review…How does the mass of an object relate to How does the mass of an object relate to

the gravitational force the object exerts on the gravitational force the object exerts on other objects?other objects?

How does the distance between objects How does the distance between objects affect the gravity between them?affect the gravity between them?

Comparing Concepts: Explain why your Comparing Concepts: Explain why your weight would change if you orbited Earth weight would change if you orbited Earth in the space shuttle but your mass would in the space shuttle but your mass would not?not?

When you stand while riding a bus, why do you When you stand while riding a bus, why do you tend to fall backward when the bus starts tend to fall backward when the bus starts moving?moving? See page 724 to check your answerSee page 724 to check your answer

How is inertia related to Newton’s First Law of How is inertia related to Newton’s First Law of Motion?Motion?

Name two ways to increase the acceleration of Name two ways to increase the acceleration of an object.an object.

Making predictions: If the acceleration due to Making predictions: If the acceleration due to gravity were somehow doubled to 19.6 m/s/s, gravity were somehow doubled to 19.6 m/s/s, what would happen to your weight?what would happen to your weight?

Name three action and reaction force pairs Name three action and reaction force pairs involved in doing your homework. Name what involved in doing your homework. Name what object is exerting and what object is receiving object is exerting and what object is receiving the forces.the forces.

Which has more momentum, a mouse running at Which has more momentum, a mouse running at 1 m/s north or an elephant walking at 3 m/s 1 m/s north or an elephant walking at 3 m/s east? Explain your answer.east? Explain your answer.

Applying Concepts: When a truck pulls a trailer, Applying Concepts: When a truck pulls a trailer, the trailer and truck accelerate forward even the trailer and truck accelerate forward even though the action and reaction forces are the though the action and reaction forces are the same size but in opposite directions. Why don’t same size but in opposite directions. Why don’t these forces balance each other out?these forces balance each other out?