Friction is a force that creates resistance to movement between two surfaces that are touching.
Have you ever gotten “rug burn” as you tried to slide across a carpet? Carpets create a lot of friction. Remember a time you went on a “slip-n-slide.” Did you get scraped at all? Probably not. This is because a slip-n-slide creates almost no friction when it is wet.
There are two basic types of friction: static friction and kinetic friction. Let’s take a look at each type:
Static friction
Static friction is a force that operates on surfaces that aren’t in motion. For example, when you pull a chair out from the table, you have to overcome static friction to get the chair to move.
When you walk static friction prevents your feet from slipping on the ground allowing you to push forward. Imagine trying to walk on slick ice!
When static friction starts to act on a round object, the object simply turns to a new spot. This reduces the effects of friction on an object with wheels, allowing it to travel much further than an object without wheels. When humans invented wheels, they found a clever way to overcome friction.
Kinetic friction
Kinetic friction is a force exerted by objects that are moving against each other. When two solid objects move next to each other, friction slows them down.
If you have ever tried to slide across the kitchen floor, you felt sliding friction between your feet and the floor. You can slide really easily in socks but if you try sliding in your sneakers, you’ll stick to the floor and not slide at all.
Fluid friction is sometimes called drag. Gases provide less friction than liquids, though there is still enough fluid friction in the air to help a plane take off or slow the descent of a sky-diver!
Physics In Action: Friction Leads to Earthquakes!
Friction plays a major role in earthquakes. An earthquake happens when the edges of two tectonic plates slide against each other. Most of the time, those plates are held in place by static friction. But, these plates have forces on all sides trying to move them around. As the forces push them in one direction, the static friction can be broken.
When enough pressure builds up to overcome the static friction between two plates, the ground literally moves as the plates slide by each other. The kinetic friction sends out heat and waves of energy – causing things to shake!
Written by Laura McCamy
Edited by Gabriel Buckley, MS Professional Natural Sciences
Illustrated by Pablo Velarde Diaz-Pache