Gravity Newton’s Laws of Motion Chapter 5: Section 4 Chapter 6: Section 2

Gravity A force of attraction between objects that 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 Gravity All objects experience an attraction toward all other objects. Because of gravity you are being pulled toward this book, your pencil, and every other object around you. Do you know why?

Earth’s Gravitational Force Is Large “It’s Truly Incomparable” Compared with “all” the objects around you, Earth has a enormous mass.

The Law of Universal Gravitation Why do objects fall toward Earth? What keeps the planets in motion in the sky? Newton Makes the Connection

The Law of Universal Gravitation states that all objects in the universe attract each other through gravitational force. The size of the force depends on the masses of the object and the distance between them.

For Example… Gravitational force increases as mass increases. Imagine an Elephant and a Cat Or imagine the Earth and the Moon Gravitational force decreases as distance increases. Gravity between you and the Earth Gravity between you and the Sun

Weight and Mass are Different Weight is a measure of the gravitational force exerted on an object. Do you know what that means? Mass is the amount of matter “Stuff” in an object, and its value does not change. If an object is moved to a place “Geographically Speaking” with a greater gravitational force (Jupiter) its weight will increase, but its mass will remain the same.

Newton’s Laws of Motion

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

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

Objects in Motion… Meaning ? This law is also sometimes called the law of inertia. Why? Inertia is the tendency of all object to resist any change in motion. Mass is a measure of inertia.

Newton’s Second Law The acceleration of an object depends on the mass of the object and the amount of force applied. Acceleration depends on mass Acceleration depends on force

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

Acceleration will increase when a larger force is exerted.

Newton’s Second Law and Acceleration are due to Gravity

Newton’s Third Law Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first. All forces act in pairs. What does this mean?

Action and Reaction Forces

“Momentum Anyone?” Momentum is a property of a moving object that depends on the object’s mass and velocity. Momentum is Conserved. Just how is this done?

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

Conservation of Momentum and Newton’s Third Law

For Review… How does the mass of an object relate to the gravitational force the object exerts on other objects? How does the distance between objects affect the gravity between them? Comparing Concepts: Explain why your weight would change if you orbited Earth in the space shuttle but your mass would not?

How is inertia related to Newton’s First Law of Motion? When you stand while riding a bus, why do you tend to fall backward when the bus starts moving? See page 724 to check your answer How is inertia related to Newton’s First Law of Motion? Name two ways to increase the acceleration of an object. Making predictions: If the acceleration due to gravity were somehow doubled to 19.6 m/s/s, what would happen to your weight?

Name three action and reaction force pairs involved in doing your homework. Name what object is exerting and what object is receiving the forces. Which has more momentum, a mouse running at 1 m/s north or an elephant walking at 3 m/s east? Explain your answer. Applying Concepts: When a truck pulls a trailer, the trailer and truck accelerate forward even though the action and reaction forces are the same size but in opposite directions. Why don’t these forces balance each other out?