Download Gravity

Gravity
Gravity is the
FORCE of
attraction
between any two
objects with
mass.
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.
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.
Watch me do this…
• When the same distance apart, which
has a stronger force of gravity between
them?
a) two apples
b) two planets
• What has a stronger force of gravity
between them?
a) two planets that are 1,000 km apart
b) 1,000,000 km apart?
Class Practice
3. 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
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.
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.
Inertia
inertia
Force of gravity
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