If you watched our episode on Newton's laws of motion, then you're practically an expert on forces, and the way they make things accelerate.
But there's something we left out -- something important when you're trying to describe how things move in real life: friction.
It stops a baseball player sliding into home plate. And it's the reason I can pick up this cup without it slipping through my fingers.
Without friction, it would be tough to do almost anything. But it also makes doing other things pretty hard. Anyone who has moved furniture knows that.
Luckily, friction is also a force, so, as physicists, we know what to do with it.
You're moving into a new house, and you ask a friend to come help out, which he does, because he's just nice like that.
And you really do need his help, because you'll have to move giant bookcases and a desk, and you can't do all of that on your own.
And about halfway through the move-in, you're rearranging the furniture in your new bedroom when you run into a problem: You're pushing and pushing on your bookcase, but it just not sliding across the floor.
So you call your friend over from the other room, and with both of you pushing, the bookcase finally starts to slide.
But it was really hard to get it moving -- and stay moving -- because there's a force working against you - stopping the bookcase from sliding: friction.
