Newton’s Laws of MotionNewton’s Laws of Motion

Gravity and MotionGravity and Motion

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.

July 20, 1969

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 the Earth, your pencil, and every toward the Earth, your pencil, and every other object around you are also being other object around you are also being pulled. Do you know why?pulled. Do you know why?

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

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 Cat Imagine the Earth and the MoonImagine 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 MoonGravity between you and the Moon

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.

Weight, a force, is measured with a spring scale.Weight, a force, is measured with a spring scale.

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. Mass is measured with a balance.Mass is measured with a balance. 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 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.

INERTIAINERTIA

Objects at “Rest”… Can moveObjects at “Rest”… Can move

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

This law is also sometimes called theThis law is also sometimes called the

law of inertia. Why?law of inertia. Why?

InertiaInertia is the tendency of all object to resist any 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. Little mass-little inertiaLittle mass-little inertia Big mass-big inertiaBig mass-big inertia

InertiaInertia – How is this related to seat belts in – How is this related to seat belts in moving vehicles?moving vehicles?

Newton’s Second LawNewton’s Second Law

The The accelerationacceleration of an object depends on 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.

AccelerationAcceleration describes the motion of an describes the motion of an object when an unbalanced force is acting object when an unbalanced force is acting on it.on it.AccelerationAcceleration depends on mass depends on mass

More mass – More forceMore mass – More force

AccelerationAcceleration depends on the force applied or depends on the force applied or needed to move the massneeded to move the mass

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 – You need more force to move Acceleration – You need more force to move more mass.more mass.

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?Think about a balloon or rocket.Think about a balloon or rocket.

““Momentum Anyone?”Momentum Anyone?”Momentum is a property of a moving Momentum is a property of a moving

object that depends on the object’sobject that depends on the object’s mass mass and velocity.and velocity.The more momentum an object has – the The more momentum an object has – the

harder it is to stop it or change it’s harder it is to stop it or change it’s direction.direction.

Think about a bowling ball and ping pong Think about a bowling ball and ping pong ballball

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

Momentum is ConservedMomentum is Conserved

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.

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?

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

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

What are the two things associated with What are the two things associated with Newton’s Third Law?Newton’s Third Law?

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

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