Modelling assumptions EOY

Applied Y1

Particle

• Mass of object is concentrated at a single point.

• Rotational forces and air resistance can be ignored.

Rod

• Mass is concentrated along a line

• No thickness

• Rigid

Lamina

• Mass is distributed across a flat surface.

Uniform body

• Mass of object is concentrated at a single point- centre of mass.

Light object

• Treat object as having zero mass

• Tension is the same at both ends of a light string.

In-extensible string

• Acceleration is the same in objects connected by a taut in-extensible string

Smooth surface

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

Rough surface

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

Wire

• Treated as one-dimensional

Smooth and light pulley

• Pulley has no mass

• Tension is the same on either side of the pulley

Bead

• Moves freely along a wire or string

Peg

• Dimensionless and fixed

• Can be rough or smooth as specified in the question

Air resistance

Usually modelled as being negligible

Gravity

• Assume that all objects with mass are attracted towards the Earth

• Earth’s gravity is uniform and acts vertically downwards.

• g is constant and is taken as 9.8ms^-1 unless otherwise stated