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. weightAre 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 objectMass- 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 gravityor

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?