Friction in nature and technology
Friction in nature and technology is both useful and harmful. Useful: thanks to friction we walk, tyres grip the road, brakes work, a nail stays in a wall and a knot holds. Harmful: machine parts wear and heat up, and energy is wasted. To reduce friction we smooth surfaces, lubricate with oil, replace sliding with rolling (bearings, wheels), or use an air cushion. To increase it we use tyre treads, sand on icy roads, brake pads and shoe soles for sport. In winter speed must be reduced because friction on ice is small and braking distance grows.
“Useful or harmful?”: pupils sort 8 situations (walking, skiing, brakes, machine shaft, warming hands, a knot, walking on ice, a wheel) into two groups. Safety: rub hands gently and avoid burning the skin.