Does Contact Area Matter?
Would a brake with a larger surface area slow the wheel more quickly?Copyright EPA
Using the same method for measuring friction that was used in the previous lesson (Discovering Friction), students design and conduct experiments to determine if the amount of area over which an object contacts a surface it is moving across affects the amount of friction encountered.
Engineers must understand how friction affects a number of situations, such as the bottom of skis in which friction is a disadvantage to hiking boots where friction provides traction. An automobile disc brake slows a car when brake pads on either side squeeze the round surface (the wheel's rotor) shown in the nearby image. The process is very similar to the way the caliper hand brakes of a bicycle squeeze the bicycle's tire rims. The friction generated impedes the rotation of the wheel, causing it to rotate more slowly until it stops altogether.
After this activity, students should be able to explain that, due to molecular attractions between some types of surfaces, the amount of friction that occurs between them varies in proportion to the amount of surface area in contact.