1. How does friction affect motion?
Forces and Friction
How does friction affect motion?

2. What Causes Friction?
Friction is the force that opposes the motion between two surfaces that touch.
The surface of any object is rough.
Even an object that feels smooth is covered with tiny hills and valleys.
The contact between the hills of valleys of two surfaces causes them to stick, resulting in friction.

3. Friction as a Force It always slows a moving object down.
Friction always works in the direction opposite from the direction the object is moving, or trying to move.
It always slows a moving object down.
Moving
Friction

4. Types of Friction
1st--Kinetic friction occurs when contact force is applied to an object and the object moves over the other
Examples:
Sliding Friction: pushing an object across a surface
Rolling Friction: between wheels and a surface
Fluid Friction: opposes the motion of objects traveling through a fluid (air or water)

5. Types of Friction
2nd Static friction occurs when force applied to an object in contact that does not cause the object to move.

6. Affecting Friction Friction increases as surfaces are made rougher.
Friction increases when the force between two objects is increased.(weight increases friction)

7. Affecting Friction
To reduce the amount of friction, apply a lubricant between two surfaces.
Motor oil, wax, and grease are examples. The oil holds the surfaces apart, and can flow between them. The reduced friction means there is less wear on the metal, and less heat produced.
Friction can also be reduced by rolling, rather than pushing, an object. (put it on wheels)

8. Affecting Friction
To increase the amount of Friction you can make the surface rougher or use more force to press the objects together
Ex. Icy road—add sand to increase friction so you can walk or drive
Use a rougher sandpaper to smooth out really rough wood.

9. Helpful Friction
Friction can be a useful force because it prevents our shoes slipping on the pavement when we walk and stops car tires skidding on the road.
It can keep your hands warm in winter
It helps clean stuck on food in pans.
It helps us smooth out rough wood

10. Harmful Friction Friction also produces heat and can be harmful.
It can cause engines to overheat, parts to wear out, and injuries to occur when skin is exposed to frictional forces.(rug burn!!!)
Causes tire tread to wear down or even your shoe tread to wear out.