The Force of Gravity

1
The Force of Gravity
2
Gravity

• Gravity- the force that pulls objects towards
  the Earth
• Free fall- when the only force acting on an
  object is gravity
• ALL objects in free fall will fall at the same
  rate of 9.3m/s2
• If you drop a bowling ball and a tennis ball off
  a building, which one will hit the ground
  first???

3
Air Resistance

• If you drop a tennis ball and a sheet of paper
  from a building, which one will hit the ground
  first?
• Air resistance- a type of fluid friction
• Is an upward force
• More surface areamore air resistance
• Increases with velocity (as objects speed up, air
  resistance increases)

4
Air Resistance

• Eventually, air resistance will equal the force
  of gravity
• Forces will become balanced (NO MORE
  ACCERATION!!)
• Object will not be able to go any faster as it
  falls
• Called terminal velocity (greatest velocity
  during free fall)

5
Universal Law of Gravitation

• The force of gravity acts between all objects in
  the universe.
• (all objects will have a gravitational force
  between them)
• Depends on mass and distance
• Bigger massmore gravity
• Less distancemore gravity

6
Gravity

• Mass vs. weight
• Are mass and weight the same thing?
• No!
• Can the mass of an object change?
• Can the weight of an object change?
• Weight- measures the force of gravity on an
  object
• Mass- measures how much matter is in an object

7
How to find weight

• Weight is a FORCE!!! We will be measuring weight
  in Newtons
• Weight mass x acceleration due to gravity
• or
• Weight mass x 9.8 m/s2

8
Example Problem

• How much would a 59 kg woman weigh on Earth?

9
Example Problem

• A bag of sugar has a mass of 2.26 kg. What is
  its weight in Newtons?
• If that same bag of sugar was on the moon, where
  the acceleration due to gravity(g) is 1.63, how
  much would the bag of sugar weigh on the moon?