Gravity

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

GravityGravity 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.

GravityGravity 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.

Watch me do this…

• When the same distance apart, which has a stronger force of gravity between them? a) two applesb) two planets

• What has a stronger force of gravity between them?a) two planets that are 1,000 km apartb) 1,000,000 km apart?

Class Practice3. When the same distance apart, which has a weaker force of gravity between them?A. the earth and the moon B. the earth and a man on the moon?

4. Which has a stronger force of gravity between them?A. two stars that are 10 miles apart B. two stars that are 100,000,000 miles

apart?

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

GravityThis 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.

Hmmm….

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

Inertia

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

Force of gravity

inertia

Inertia

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!

Watch me do this…

• What force keeps Earth in orbit around the sun?

• Gravity!

inertia

Class Practice

8. In what direction does an object in space tend to move?

a) In a curved path

b) Inward

c) In a straight line

d) 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?

a) The force of gravity would be greater

b) The force of gravity would be unchanged

c) The force of gravity would be less

d) There would be no force of gravity

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?

a) Earth would escape into space

b) Earth would fall into the sun

c) Earth would remain in its orbit

around the sun

a) Earth would stop moving

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