Chapter 8 - Modelling in mechanics

Particle

Definition - dimensions of the object are negligible

Assumptions - mass of the object is concentrated at a single point, rotational forces and air resistance is ignored

Rod

Definition - one dimension is negligible, like a pole or beam

Assumptions - mass is concentrated along a line, no thickness, rigid

Lamina

Definition - an object with an area but negligible thickness, like paper

Assumptions - mass is distributed across a flat surface

Uniform body

Definition - mass is distributed evenly

Assumptions - mass is concentrated at the centre of mass

Light object 

Definition - mass of the object is small compared to others 

Assumptions - object has zero mass, tension is equal throughout 

Inextensible string 

Definition - a string that does not stretch under load

Assumptions - acceleration is the same in objects connected by a taut string 

Smooth surface

Definition - surface with no friction

Assumptions - no friction between the surface and any object on it

Rough surface

Definition - a surface which is not smooth

Assumptions - objects in contact with the surface experience a frictional force

Smooth and light pulley

Definition - there is no friction in the pulley

Assumptions - pulley has no mass, tension is the same on either side of the pulley

Air resistance

Definition - resistance experienced as an object moves through the air

Assumptions - modelled as negligible