"What can slow things down?" Return to list of pracs

Aim: This is an activity to begin a discussion about friction.

Equipment: The equipment includes...  

• friction materials: sheet of sand paper, cloth, paper, fur, cellophane etc;
• sheet of glass (or window);
• masking tape;
• wooden blocks or erasers..

Method: Using the masking tape, secure a sheet of the material onto a table top. Rub the wooden block on the surface and compare which surface is easier to move along. You can display your results on a chart similar to the following.. Place a sample of the material along the line...

Background knowledge: A discussion about what type of surface made it hard to move. Feel the surface with your hands. What do you notice about the type of surface? The rough surfaces should be the surfaces that are hard to move the blocks along. This is because if you look really close at the surface of a rough surface, the "landscape" is extremely jacked. The surface of a smooth surface is very flat. The particles on one surface collide with the particles on the other surface and the more collisions the more friction exists. Therefore, a smooth surface rubbing against a smooth surface results in low amounts of friction. Also friction can be reduced by using (a) lubricants (oils etc); (b) streamlining; (c) reducing the weight of the object; or (d) reducing the amount of area one surface has to rub against the other surface.