Friction is a force that opposes motion and yet it's necessary for some types of motion. When you walk, your foot pushes back on the floor and the floor pushes your foot forward. Friction is the force between two surfaces moving past each other, in this case your shoes and the floor. If there was no force of friction your shoes would keep sliding back along the floor rather than gripping and pushing you forward.
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Friction is a force that opposes motion and yet it's necessary for some types of motion. When you walk, your foot pushes back on the floor and the floor pushes your foot forward. Friction is the force between two surfaces moving past each other, in this case your shoes and the floor. If there was no force of friction your shoes would keep sliding back along the floor rather than gripping and pushing you forward.
Friction between car tires and the road allows the tires to grip the road and propel a car forward instead of just spinning. It also allows the car to turn corners and to stop.
Knives and saw blades use friction to cut through things and sandpaper and files use friction to remove material and shape objects. Pencils leave graphite on paper because of friction between the two surfaces.
The friction of electrons moving through a conductor is called resistance. Heat and light generated by resistance lights incandescent light bulbs and produces the heat in stove burners and oven heating elements that cook food. Heat is also produced by resistance in water heaters, clothes dryers and space heaters.
Friction is increased by making surfaces rougher and its decreased by making surfaces smoother. Oil and grease fill in the irregularities in rough surfaces and make them smoother.
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