Whenever two things rub together, some of the energy they have is lost to friction. Basically, in things like car engines, the wheels of your skates, and the chain of your bike, friction is a force that slows you down. In order to overcome friction, you have to work harder. However, the energy doesn't just disappear — it's turned into heat! Try rubbing your hands together as fast as you can. Pretty soon, they'll be burning up!

As it turns out, the rougher two surfaces are, the more friction there is between them when they rub together. By making things really smooth, or by adding lubricants like grease and oil, engineers work hard to reduce friction and in the long run, save energy.

Friction isn't always bad though. If you've ever tried to start running on a wet floor, you know that too little friction can just make you slip and slide. You need a certain amount of friction to get a grip in order to get yourself going. That's why winter car tires usually have deeper treads than regular tires. The extra grooves make the surface rougher and help them get a grip on ice and snow. Ever wonder why sneakers always have treads on the bottom? They're there to give you some extra grip when you run and play.

Now that we've got you thinking about the force that makes you grip and slip, it's time to observe and record.