Mechanics Modelling Assumptions

Rotational Forces and Air Resistance can be ignored

• Smooth surface

• Peg

• Particle

• Rough Surface

Assume that all objects with mass are attracted towards the Earth

• Gravity

• Inextensible string

• Wire

• Air resistance

Assume that there is no friction between the surface and any object on it

• Lamina

• Smooth surface

• Rod

• Particle

Treat object as having zero mass

• Light object

• Uniform body

• Bead

• Particle

Mass of the object is concentrated at a single point at the centre of mass

• Air resistance

• Peg

• Wire

• Uniform body

Rigid (does not bend or buckle)

• Air resistance

• Particle

• Rod

• Smooth surface

Objects in contact with the surface experience frictional force if they are moving or acted on by a force

• Particle

• Rough surface

• Smooth surface

• Lamina

Usually modelled as being negligible...

• Air Resistance

• Gravity

• Bead

• Wire

Object with area but negligible thickness e.g. sheet of paper

• Smooth and light pulley

• Particle

• Rod

• Lamina

Has no mass and tension is the same on each side...

• Air resistance

• Wire

• Smooth and light pulley

• Lamina