Gravity Terms

1
Gravity Terms

• Gravity Inertia
• Orbits Ellipse

2
How do the planets remain in their orbits ?

• What two factors keep the planets in their
  orbits?
• What is gravity?
• What is inertia?
• What two factors does the strength of the pull of
  gravity depend upon?

3
Gravity

• All objects, from the atom to the largest family
  of stars, possess gravity.
• Gravity is a force that attracts all objects
  towards each other.
• The strength of the pull of gravity between two
  objects depends on two factors.
• These two factors are the product of the masses
  of the objects and the distance between them.

4
Gravity

• As the product of the masses increases, the pull
  of gravity also increases.
• If the distance between the two objects
  increases, then the pull of gravity between them
  decreases.
• All objects in our solar system travel around the
  sun in paths called orbits.
• Planets orbit around the sun, and moons are in
  orbit around planets.

5
Gravity

• Scientist Sir Isaac Newton discovered 3 Laws of
  Motion.
• His 1st Law of Motion states that an object in
  motion will tend to stay in motion at the same
  speed and direction unless acted on by an outside
  force.
• The tendency of objects to keep doing what they
  were doing is called inertia.

6
Gravity

• Inertia tends to lead planets to follow a
  straight path at a certain speed unless acted on
  by an outside force. This outside force is the
  gravity of the sun.
• While the gravity of the sun pulls the planet
  towards it, the speed and direction (inertia) of
  the planet pushes it forward.
• When the forces of gravity and inertia are
  balanced, the planet follows a curved path around
  the sun.

7
Quick Check

• What force keeps Earth in orbit around the sun?
• A. a pull by one object that is in contact with
  another object.
• B. a push by one object that is in contact with
  another object.
• C. mass
• D. gravity

8
Quick Check

• What affects the force of gravity between two
  objects?
• A. the product of their masses and the distance
  between them
• B. only the distance between them
• C. only the sum of their masses
• D. the mass of the larger object

9
Quick Check

• 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

10
Quick Check

• 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 unchanged.
• B. The force of gravity would be greater.
• C. The force of gravity would be less.
• D. There would be no force of gravity.

11
Quick Check

• If the force of gravity between Earth and the sun
  were greater than Earths 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.
• D. Earth would stop moving.