Air resistance — Physical education, 7–10 years
Air can push against moving things. This helps explain why a paper sheet falls slowly and why a parachute opens.
What air resistance does
Air is hard to see, but it takes up space and can push back on moving objects. The faster an object moves, or the more air it faces, the stronger this slowing effect usually is. A flat sheet feels more resistance than a crumpled one.
Why air resistance matters
Without air resistance, falling objects would speed up in a much simpler way, and a parachute would not slow a person safely. People learned to use the air rather than ignore it: parachutes spread out, and racing cyclists make their bodies narrow. The problem is controlling speed.
A fair falling test
Take two same-size paper sheets. Leave one flat and scrunch the other into a ball, then drop them together from the same height. The ball usually lands first because less of its surface meets the air. The paper’s mass is nearly the same; its shape changes the resistance.
The common mistake
It is reasonable to think the heavier object must always fall faster, because gravity pulls on it more strongly. But air resistance can change what we observe. A large, light parachute may fall slowly, while a small heavy stone quickly reaches the ground.
Where we use it
Parachutes use a large surface to create lots of air resistance and slow a fall. Birds and aeroplanes have shapes that help air flow around them, while cyclists wear close-fitting clothes to reduce resistance. In each case, the shape is chosen for a particular speed or safety need.
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