Tires aren't just for cars and trucks. In "inner tubing," you sit or lie down on a giant donut-shaped balloon and slide down the snowy, slippery hill. It's called an "inner" tube because it's from inside a truck tire. People first started snow tubing in 1820 in Switzerland, a long time before cars or trucks -- so where did they get their tubes? More importantly, what happens when you spin as you slide?