1. Page 38 and 39 Date: October 26, 2012 Notes– 3
Page 38 and 39 Date: October 26, 2012 Notes– 3.2 Weight, Gravity, and Friction

2. Gravity
A force that pulls every mass toward every other mass
The force that pulls everything toward the center of the Earth
Down is the direction of gravity’s force

3. Weight vs. Mass The force of gravity depends on how much mass you have
The larger the planet you are on, the greater the force of gravity
Weight - the force created by gravity on objects (weight depends upon your mass)
Mass –constant throughout the universe (your mass doesn’t change)

4. Fw=mg Fw = weight force (N) m = mass (kg)
g = acceleration due to gravity (m/sec2)
(9.8 m/sec2 on Earth)

6. Law of Universal Gravitation:
The force of gravity increases when the mass of the objects increases. The force of gravity also increases when the objects get closer together.

7. Friction The force that results from relative motion between objects
A force that always opposes motion

8. Kinds of Friction
Air friction- air moving around objects creates an opposing force
Sliding friction- when two surfaces rub against each other
Viscous friction- objects that move in water or other fluids create this
Rolling friction- caused by one object rolling over another

9. Net Force
Total force subtracts friction from gravity Net force is what is left
Friction reduces acceleration
All machines have friction