They make it less accurate

Dimensions of the object are negligible

All dimensions but one are negligible - a rod will have length but no height or width

The object has area but negligible thickness

Mass of an object is very small - e.g. a string or pulley

It doesn't stretch under load

A rigid thin length of metal

Smooth and light

A particle with a hole in it for threading on a wire or string

A support from which a body can be suspended or rested

Resistance experienced by an object as it moves through air, slowing it down

A force of attraction between all objects. Acceleration due to gravity is denoted as g (9.8m/s²)

Mass of an object is concentrated at a single point, Rotational forces and air resistance are ignored

Mass is concentrated along a line, No thickness, Rigid (doesn't bend or buckle)

Mass is distributed across a flat surface

Mass of the object acts at a single point in the centre of the body

Zero mass, Tension is equal at both ends of a string

Two objects at either end of an inextensible string have the same acceleration

No friction between the surface and an object moving on it

Objects moving on a rough surface experience friction

One-dimensional

No mass, Tension is the same on either side of the pulley

Moves freely along a wire or string , Tension is the same on either side of a bead

Dimensionless and fixed

Negligible, unless stated otherwise