Newton’s Laws of Motion Gravity and Motion

Gravity A force of attraction between objects that is due to their masses. 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. July 20, 1969

All Matter Is Affected by Gravity All objects experience an attraction toward all other objects. All objects experience an attraction toward all other objects. Because of gravity you are being pulled toward the Earth, your pencil, and every other object around you are also being pulled. Do you know why? Because of gravity you are being pulled toward the Earth, your pencil, and every other object around you are also being pulled. Do you know why?

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

The Law of Universal Gravitation Why do objects fall toward Earth? Why do objects fall toward Earth? What keeps the planets in motion in the sky? 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. Gravitational force increases as mass increases. Imagine an Elephant and a Cat Imagine an Elephant and a Cat Imagine the Earth and the Moon Imagine the Earth and the Moon Gravitational force decreases as distance increases. Gravitational force decreases as distance increases. Gravity between you and the Earth Gravity between you and the Earth Gravity between you and the Moon Gravity between you and the Moon

Weight and Mass are Different Weight is a measure of the gravitational force exerted on an object. Weight is a measure of the gravitational force 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, and its value does not change. Mass is the amount of matter “Stuff” in an object, 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 Speaking” with a greater gravitational force (Jupiter) its weight will increase, but its mass will remain the same. 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 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. 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.

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

Objects in Motion… Meaning ? Objects in Motion… Meaning ? This law is also sometimes called the law of inertia. Why? law of inertia. Why? Inertia is the tendency of all object to resist any change in motion. Inertia is the tendency of all object to resist any change in motion. Mass is a measure of inertia. Mass is a measure of inertia. Little mass-little inertia Little mass-little inertia Big mass-big inertia Big mass-big inertia Inertia – How is this related to seat belts in moving vehicles? Inertia – How is this related to seat belts in moving vehicles?

Newton’s Second Law The acceleration of an object depends on the mass of the object and the amount of force applied. The acceleration of an object depends on the mass of the object and the amount of force applied. Acceleration describes the motion of an object when an unbalanced force is acting on it. Acceleration describes the motion of an object when an unbalanced force is acting on it. Acceleration depends on mass Acceleration depends on mass More mass – More force More mass – More force Acceleration depends on the force applied or needed to move the mass Acceleration depends on the force applied or needed to move the mass

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

Acceleration – You need more force to move more mass.

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. 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? All forces act in pairs. What does this mean? Think about a balloon or rocket. Think about a balloon or rocket.

“Momentum Anyone?” Momentum is a property of a moving object that depends on the object’s mass and velocity. Momentum is a property of a moving object that depends on the object’s mass and velocity. The more momentum an object has – the harder it is to stop it or change it’s direction. The more momentum an object has – the harder it is to stop it or change it’s direction. Think about a bowling ball and ping pong ball Think about a bowling ball and ping pong ball Momentum is Conserved. Just how is this done? Momentum is Conserved. Just how is this done?

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

For Review… How does the mass of an object relate to the gravitational force the object exerts on other objects? 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? 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? 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? How is inertia related to Newton’s First Law of Motion? Name two ways to increase the acceleration of an object. Name two ways to increase the acceleration of an object. What are the two things associated with Newton’s Third Law? What are the two things associated with Newton’s Third Law?

Name three action and reaction force pairs involved in doing your homework. Name what object is exerting and what object is receiving the forces. 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. Which has more momentum, a mouse running at 1 m/s north or an elephant walking at 3 m/s east? Explain your answer.