GRAVITY

1
GRAVITY

• Chapter 3
• Section 2

2
The Law of Gravitation

• You exert an attractive force on everything
  around you and everything is exerting an
  attractive force on you.
• This attractive force is called gravity.
• Anything that has mass is attracted by the force
  of gravity.
• The Law of Gravitation states that any two masses
  exert an attractive force on each other.

3
The Law of Gravitation

• Gravitation force depends on two things
• The mass of the two objects
• The distance between the two objects
• Why do you suppose the Earth exerts a force on
  you that you can feel, but you cant feel the
  force the desk is exerting on you?

4
Gravity a basic force

• There are four basic forces
• Gravity
• Electromagnetic force
• Nuclear force Strong
• Nuclear force Weak

5
Gravitational Acceleration

• When objects fall, the gravitational pull is 9.8
  m/s2
• When a falling object is only affected by gravity
  it is said to be in free fall.

6
Gravitational Acceleration

• If you drop a bowling ball and a marble off a
  bridge, which would hit the water first?
• Things to consider

7
Gravitational Acceleration

• Force of gravity is greater on the bowling ball
  because of its larger mass.
• The larger mass means it has a larger inertia so
  more force is needed to change its velocity.
• Gravitational force on the marble is smaller
  because it has a smaller mass
• The inertia on the marble is less and less force
  is needed to change the velocity.
• Therefore, all objects fall with the same
  acceleration!

8
Weight

• Even if you are standing still and you have zero
  acceleration, the force of gravity is still
  present.
• Weight is the gravitational force exerted on an
  object.
• Capital W stands for weight.
• Gravitational force mass x (acceleration due to
  gravity)

9
Weight

• Because the gravitational force is the same as
  the weight and the acceleration due to gravity,
  the equation can also be written as
• W (m)(9.8 m/s2)

10
Weight Mass

• Weight and mass are not the same thing.
• Weight is a force
• Mass is a measure of the amount of matter an
  object contains.
• The greater the weight, the greater the
  attraction between the object and Earth.

11
Weightlessness

• To be nearly weightless, you would have to be far
  from the Earth.
• Astronauts experience this feeling when they are
  in space.