Sci. 1-3

Friction: A Force that Opposes Motion

Pages 15- 20

A. Friction- a force that opposes motion between surfaces that are touching.

B. All objects’ surfaces have hills and valleys. Even the objects that look and feel smooth have microscopic hills and valleys.

C. Rougher surfaces create more friction because they have bigger hills and valleys to catch on the other object.

D. Greater force creates more friction. More force causes the hills and valleys to come into closer contact. Heavier objects create more friction.

E.Types

of

Friction

1) Sliding friction- pushing a object across an object. Sliding friction is the force that stops motion.

2) Rolling Friction- using wheels. Rolling friction is usually less than the force of sliding friction. Therefore it is usually easier to move objects with wheels.

3) Fluid Friction- the force between an object and a liquid such as water, milk, or gases such as air and helium. There is less force between fluid friction than sliding friction.

4) Static Friction- a force applied to an object but does not cause the object to move.

F. One way to reduce friction is to add lubricants- motor oil, wax or grease

G. Changing types of friction can reduce friction. Going from sliding friction to rolling friction. (Add wheels or ball bearings)

H. Also smoothing the surface reduces friction because there are less hills and valleys to catch on the object.

I. Increasing Friction

1) Roughen surfaces- sand on icy roads, batting gloves on bats

2) increase the force pushing on surfaces- increase weight