Post on 28-Dec-2015
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?