Things slide when surfaces are smooth or slippery. If they are rough or sticky surfaces, they don’t slide because there is too much friction. Rub your hands together really fast. Our hands are rough so they don’t slide very easily - there is a lot friction, and that’s why it feels warm. Friction slows things down or keeps them from moving, and also makes heat.
Think about how a train moves. The wheels on the train spin around and around on the smooth, or slippery track. If we want the train to move, we put sand on the track to make it rough. Now the train can move forwards or backwards. This is just like car wheels trying to move on slippery ice. They just spin in place because the ice is not sticky - it’s smooth. We spread sand on the ice to make it less slippery and stickier.
When the train is in motion and the wheels are turning, we use the brakes to stop. The brakes grab the wheels, and the two rough surfaces create friction to slow the wheels.
Information provided by Children’s Museum of Virginia
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