G5 – Friction: Good or Evil Lower_Level – 02

Ouch! This person has fallen off his bike. Friction is what caused the riders injury, not the fall. Friction takes place when two objects rub together. In this case, it was the rider’s leg and the ground. Bike riders call this type of injury road rash. In the case of road rash, friction is not good. Is that always the case?

 Friction is a force that works in the opposite way of motion. It happens between two surfaces that are touching. In the case of the bike rider, the two surfaces were his leg and the ground. At times like these, you could say friction opposes movement.

There are many cases, though, when people rely on friction. When you push the brakes on your bike, you and the bike slow down due to friction. It is the brake pads that rub on the metal rim that makes this happen. Athletes wear special shoes to keep their feet from sliding on different kinds of surfaces. Basketball shoes have rubber mixes that increase friction on the smooth wooden surface of the courts. Soccer players have cleats on their shoes to keep them from sliding on the grass. In these cases, friction is a good thing.

Friction can also work against us. Think about a world where there is no friction. You would not be able to walk. Each time you tried to push forward, your foot would slide backwards. You cannot even sit in a chair. Without friction between your clothing and the seat, you would slide onto the ground. Friction takes place because no surface is smooth. Even surfaces that appear to be smooth are bumpy when viewed under a microscope. All those tiny grooves catch and grab the tiny grooves on another surface. It is this action between the surfaces that causes friction.