1. Gravity

2. 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.

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

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

5. The Law of Universal Gravitation Discovered by Newton in the late 1600’s while he watched an apple fall from a tree Discovered by Newton in the late 1600’s while he watched an apple fall from a tree 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 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

6. Universal Gravitation: Two bodies attract each other with equal and opposite forces Universal Gravitation: Two bodies attract each other with equal and opposite forces 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. 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., The Law of Universal Gravitation

7. 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

8. 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 Or imagine the Earth and the Moon Or 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 Sun Gravity between you and the Sun

9. 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. Do you know what that means? Do you know what that means? 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.

11. Free Fall Occurs when the only force acting on an object is gravity Occurs when the only force acting on an object is gravity All objects in free fall accelerate at the same rate All objects in free fall accelerate at the same rate W = mg g = 9.8 m/s 2 Derived from Newton’s 2 nd law: F=ma

12. Acceleration are due to Gravity Acceleration due to gravity = g = 9.8 m/s 2

13. Falling Objects

14. Misconceptions 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 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 Without air resistance, all objects will drop at equal rates Skydivers are not in “free fall” because air resistance is also acting on them. Skydivers are not in “free fall” because air resistance is also acting on them.

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

17. Orbital Motion http://phet.colorado.edu/en/simulation/gravity-and-orbits

18. 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?