1. Friction
Friction is a force that opposes motion between two surfaces that are in contact
Frictions occurs because surfaces are covered with microscopic hills and valleys. (Even surfaces that feel smooth)
The hills and valleys on one surface stick to the hills and valleys of the other surface

2. 2 Factors that affect the amount of friction
Amount of force pushing the surfaces together
Ex. Heavy and light book
Roughness on the surfaces
Ex. Rubbing sandpaper pieces together

3. Kinetic vs. Static Friction
Kinetic friction is friction between moving surfaces
Static is friction is when a force is applied to move an object but it doesn’t move
Static friction disappears once the object starts to move

4. Ways to reduce friction
Apply a lubricant (oil, wax grease)
Change from sliding kinetic friction to rolling kinetic friction

6. Ways to Increase Friction
Make surface rougher
Increase the force pushing the surfaces together