text: Friction occurs anytime there is resistance when two objects touch.  \n\nThe rougher the texture of an object, the more friction it can produce.  All the little tiny rough spots catch on each other (imagine running your hand over, say, a piece of sandpaper...you can feel the grains of sand catching at your hand; it's a lot different than running your hand over something smooth, like polished metal)  The rough surfaces catch at each other and stick together.  That's friction.\n\nFriction is the reason we can walk on the ground - otherwise, we'd slip and slide everywhere, as if we were on ice.  (Really, really slippery ice :p)\nFor another example, when you're driving down the road, friction between your tires and the road is what keeps your wheels rolling along.  \nIf you hit a patch of ice, and your wheels slip, it's because there's not enough friction to overcome the force of your wheels turning.  Ice is slippery - there's less friction between tires and ice than tires and the paved road.