Mechanincs modelling assumptions

What is the particle model of an object?

Dimensions of the object are negligible.

What does the rod model mean?

All dimensions but one are negligible, like a pole or a beam.

What does uniform body mean?

Mass is distributed evenly.

What does light object mean?

Mass of the object is small compared to other masses, like a string or a pulley.

What is an inextensible string?

A string that does not stretch under load.

What is a wire?

Rigid thin length of metal.

What is a peg?

A support from which a body can be suspended or rested.

What are the modelling assumptions of a particle?

• Mass of the object is concentrated at a single point

• Rotational forces and air resistance can be ignored

What are the modelling assumptions of a rod?

• Mass is concentrated along a line

• No thickness

• Rigid (does not bend or buckle)

What are the modelling assumptions of uniform bodies?

Mass of the object is concentrated at a single point at the geometrical centre of the body - the centre of mass.

What are the modelling assumptions of light objects?

Treat object as having zero mass.

What are the modelling assumptions of inextensible strings?

Acceleration is the same in objects connected by a taut inextensible string

What are the modelling assumptions of light strings?

Tension is the same at both ends of the string

What are the modelling assumptions of a smooth surface?

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

What are the modelling assumptions of a rough surface?

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

What are the modelling assumptions of a wire?

Tareated as one-dimensional.

What are the modelling assumptions of a smooth and light pulley?

• Tension is the same on either side of the pulley

• Pulley has no mass

What are the modelling assumptions of a peg?

• Dimensionless and fixed

• Can be rough or smooth as specified in question