Forces and Motion

Friction - Good or Bad?

Friction can be bad.

Whenever an object (bicycle, car, train) is moving,
friction provides an opposing force which tries to slow the object down.

The largest force is air resistance.
This is friction caused by the moving object pushing the air out of its way.
Air resistance causes kinetic energy to be transferred into heat.
If an object is moving very fast (for example a meteor)
the amount of heat can be so great that the object burns up.

Air resistance can be reduced by changing the shape of the object
so that it can push the air away more easily. This is called streamlining.
The faster an object is moving, the more air resistance it meets
and so streamlining becomes more important.
A rocket is more streamline than a bus.

A small friction force comes from mechanical surfaces
rubbing over each other in engines and wheel bearings.
This friction is kept small by lubricating the surfaces (oil them).

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