1. Gravity is the FORCE of attraction between any two objects with mass.

2. Gravity Gravity depends on two things: The mass of the two objects.
The distance between them.
The more mass two objects have, the stronger the pull of gravity.

3. Gravity Gravity depends on two things: The mass of the two objects.
The distance between them.
The farther apart they are, the weaker the pull of gravity.

4. Watch me do this…
When the same distance apart, which has a stronger force of gravity between them?
two apples
two planets
What has a stronger force of gravity between them?
two planets that are 1,000 km apart
1,000,000 km apart?

5. Class Practice
3. When the same distance apart, which has a weaker force of gravity between them?
the earth and the moon
the earth and a man on the moon?
4. Which has a stronger force of gravity between them?
two stars that are 10 miles apart
two stars that are 100,000,000 miles apart?

6. Who introduced the theory of gravity?
Sir Isaac Newton
He theorized (he thought) that the same force that made an apple fall from a tree must also pull the moon toward Earth

7. This is Newton’s Law of Universal Gravitation.
Gravity
This is Newton’s Law of Universal Gravitation.
All objects in the universe attract each other by the force of gravity. The strength of this force depends on the masses of the objects and the distance between them.

8. Hmmm….
If gravity is a force that pulls things toward Earth, why doesn’t the moon crash into Earth?

9. Inertia
Inertia is the tendency of a moving object to continue in a straight line or a stationary object to remain in place.

10. Force of gravity
Inertia
inertia

11. Orbits!
Orbit: The path of an object as it revolves around another object in space.
Question: What two forces work together to create an orbit?
Gravity and inertia!

12. Watch me do this… What force keeps Earth in orbit around the sun?
Gravity!
inertia

13. Class Practice
8. In what direction does an object in space tend to move?
In a curved path
Inward
In a straight line
Backward
9. How would the force of gravity between Earth and the sun be affected if the mass of Earth were greater than it is?
The force of gravity would be greater
The force of gravity would be unchanged
The force of gravity would be less
There would be no force of gravity

14. Watch me do this…
If the force of gravity between Earth and the sun were greater than Earth’s inertia, what would happen to Earth?
Earth would escape into space
Earth would fall into the sun
Earth would remain in its orbit
around the sun
Earth would stop moving

15. Class Practice
10. What affects the force of gravity between two objects?
11. Of the 8 planets, why does the sun have the least gravitational attraction to Neptune?
12. How would the gravitational force between Earth and an astronaut change as the astronaut traveled FURTHER away from Earth?
Gravitational pull on the astronaut would increase
Gravitational pull on the astronaut would decrease
There would be no change in the gravitational pull between the Earth and the astronaut
Gravitational pull on Earth would increase