1. Gravity

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.

3. 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?

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 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.

6. The Law of Universal Gravitation
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

7. The Law of Universal Gravitation
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.
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8. 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

9. 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.

11. 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
Without air resistance, all objects will drop at equal rates
Skydivers are not in “free fall” because air resistance is also acting on them.

12. Free Fall Occurs when the only force acting on an object is gravity
All objects in free fall accelerate at the same rate

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

14. Video: Are Astronauts Weightless

15. Video: Zero G Jet

16. Video: Zero G Jet 2

17. Acceleration are due to Gravity
Acceleration due to gravity = g = 9.8 m/s2

18. Video: Misconceptions about falling objects

19. Video: No Air Resistance

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

21. Video: Terminal Velocity

22. 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?

23. Other Videos: