Gravity Gravity l A force of attraction between

Gravity

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

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 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. http: //phet. colorado. edu/en/simulation/gravity-force-lab

The Law of Universal Gravitation Discovered by Newton in the late 1600’s while he watched an apple fall from a tree l He said that the force that pulled the apple to the ground was the same force that keeps the moon and earth in it’s orbit l

The Law of Universal Gravitation l Universal Gravitation: Two bodies attract each other with equal and opposite forces , l The magnitude of this force is proportional to the product of the two masses and is also proportional to the inverse square of the two bodies.

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

Weight and Mass are Different l l l 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.

Misconceptions l l l Astronauts are not experiencing weightlessness. They are in free fall along with all the other objects around them. Since they are all “falling” at the same rate Without air resistance, all objects will drop at equal rates Skydivers are not in “free fall” because air resistance is also acting on them.

Free Fall l Occurs when the only force acting on a object is gravity l All objects in free fall accelerate at the s rate

Projectile Motion Has 2 components l Consists of vertical and horizontal velocities l Horizontal = launch l Vertical = gravity l Causes a curved path l This is why you should always aim a target l

Video: Are Astronauts Weightless

Video: Zero G Jet

Video: Zero G Jet 2

Acceleration are due to Gravity Acceleration due to gravity = g = 9. 8 m/s 2

Video: Misconceptions about falling objects

Video: No Air Resistance

Terminal Velocity Both gravity and air resistance act on falling objects l Objects accelerate as they fall l If/when air resistance equals the gravitational force (balances the weight) no more acceleration occurs l When acceleration stops, a maximum velocity is reached. Its called terminal velocity. l

Video: Terminal Velocity

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

Other Videos: l http: //www. xenia. k 12. oh. us/olc/folder. aspx ? id=12350&s=314&c=2687