Rubbing slows things down — Physical education, 4–6
When two surfaces rub, they can slow movement; rough surfaces usually give more grip than smooth ones.
Idea: rubbing can slow movement
A toy car rolls more easily on a smooth floor than on a carpet. The surfaces rub against the wheels, and this rubbing, called friction, can slow the car or help it stop.
Why friction matters
Without enough friction, our feet would slide when we walk and crayons would not mark paper. People discovered that rougher surfaces grip better, while smooth surfaces help objects slide or roll more easily.
Example: a toy car
Mark a start line and push the same toy car gently on a tile floor. It travels 120 centimetres; on a carpet, the rubbing is greater and it travels only 60 centimetres before stopping.
Trap: more friction is not always better
It is tempting to think that more grip always helps, because it stops us slipping. But too much friction can make a drawer hard to open or a wheel hard to turn, so the useful amount depends on the job.
Use: shoes and brakes
The rough patterns on shoe soles help us grip the ground. Bicycle and car brakes use friction to slow the wheels, while smooth wheels and tracks help some machines move with less rubbing.
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