The Force of Gravity
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???
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 area=more air resistance
– Increases with velocity (as objects speed up, air
resistance increases)
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)
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 mass=more gravity
– Less distance=more gravity
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
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
Example Problem…
• How much would a 59 kg woman weigh on
Earth?
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?