Have you ever slid across a wooden floor in your socks and then stopped fast on a carpet? The thing that slowed you down is called friction. Friction is a force that happens whenever two surfaces rub against each other.

Every surface is bumpier than it looks. Even a shiny table has tiny bumps you cannot see. When two surfaces slide past each other, their little bumps catch and drag. That dragging is friction, and it always pushes against the direction you are trying to move.

Rough surfaces make a lot of friction, and smooth surfaces make only a little. That is why a ball rolls a long way across smooth ice but stops quickly on rough grass. The grass grabs the ball much more than the slippery ice does.

Friction can be a helper or a bother. It helps your shoes grip the ground so you do not slip, and it lets the brakes on a bike squeeze the wheel to stop. Without any friction at all, you could never walk, write, or hold a cup.

Sometimes we want less friction so things can slide easily. People add oil to squeaky door hinges and slippery wax to sleds. The oil fills in the tiny bumps so the surfaces glide instead of catching.

So next time something rolls to a stop, remember it was friction doing the work. Look for it everywhere, in the grip of your sneakers, the drag of a slide, and the squeal of a stopping car.