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Forces and Motion

Friction.

What is Friction?

Friction is an opposing force. Friction acts in the
opposite direction to a force that is applied to an object.

Where does Friction Occur?

Friction occurs where two solid objects rub against each other
or
where a liquid or gas is pushed out of the way of a moving object.
The amount of friction
always increases as the velocity of the object increases.

How much Friction is there between Two Solid Objects?

For two solid objects, the amount of friction depends
on how well the surfaces grip each other.
Tyres on a road usually have very high friction (they don't slide)
but skates on ice have very low friction (they slide easily).

How much Friction is there between a Solid and a Liquid?

For a solid object moving through a liquid, the amount of friction
depends on the objects velocity, shape, surface area
and the viscosity (thickness or thinness) of the liquid.

An object moving through a high viscosity liquid (syrup)
will have a high friction, and an object moving
through a low viscosity liquid (water) will have a low friction.

How much Friction is there between a Solid and a Gas?

For a solid object moving through air, the amount of friction
depends on the objects velocity, shape and surface area.
This type of friction is called "air resistance" or "drag".
A parachute will have a very high air resistance
but a rocket is streamline and has a very low air resistance.

Is friction good or bad?

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