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In mechanics, it is necessary to take a real life problem and put it in mathematical language. This process is known as modelling.


When modelling, we often make assumptions to make the mathematics simpler.

A particle is a body whose entire weight acts through a single point. A particle doesn’t suffer from air resistance.

A lamina is a two dimensional body, it is the 2-dimensional equivalent of a particle. All of the weight acts through one plane.

A body is said to be uniform if it has constant density. A body is non-uniform if the density varies throughout.

A smooth surface is one which has no friction.

A rough surface is one upon which friction acts.

We say an object is light if it has no mass. So no weight acts on a light body.

An inextensible string is a string which has a fixed length- it is impossible to stretch.

A rigid body is a body which is not a point and whose shape is fixed.

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