Wheels help things roll — Engineering, 4–6 years
A wheel turns around a centre, letting an object move along the ground with less scraping. This simple idea appears in toys, trolleys, bicycles, and many other things that need to travel.
Turning instead of scraping
When you push a box, its bottom scrapes along the floor. A wheel turns, so the part touching the floor keeps moving around and around instead of scraping forward. With wheels and an axle through their centres, a cart can move more easily.
Why put wheels on a cart?
People have needed to move heavy things without lifting them. Dragging makes the floor and the object rub against each other, which makes movement harder. Wheels change much of that rubbing into rolling, so a push can move a load farther and more smoothly.
A toy box on wheels
Push an empty box across the floor and notice how it rubs and stops. Attach four bottle tops as wheels, using two straight sticks as axles, then push again. The wheels turn under the box, so the box travels more easily than when its flat bottom scrapes.
“Any round thing is a wheel”
A ball is round, so it is natural to expect it to work like a wheel. But a wheel usually turns around a fixed centre and stays connected to the object; a loose ball rolls in many directions. Shape matters, but the centre and attachment matter too.
Bikes, suitcases, and trolleys
A bicycle uses wheels to travel, and its pedals turn the wheels through parts connected to the axles. A suitcase or trolley uses small wheels so you can pull it instead of lifting it. Wheels do not make every surface easy, but they help most on a firm, fairly smooth one.
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