Stats and Mechanics

Particle

Dimensions of object are negligible, mass of the object is concentrated at a single point.

Rod

All dimensions but one are negligible and it is rigid (e.g. a beam), mass is concentrated along a line.

Lamina

Object with area but negligible thickness (e.g. paper), mass distributed across a flat surface.

Uniform body

Weight acts through the centre of the body.

Light object

Mass of the object is small compared to other masses, has zero mass.

Light String

Tension is the same everywhere on the string

Inextensible string

String does not stretch under load, so acceleration of connected particles is the same.

Smooth and light pulley

Pulley has no mass, so tension is the same either side of the pulley

Rigid body

A body that maintains a constant shape.