Mechanics: Key Terms

Question 1

Particle

Answer 1

Dimensions of the object are negligible

Assumptions:
1. Mass of the object is concentrated at a single point
2. Rotational forces and air resistance can be ignored

Question 2

Rod

Answer 2

All dimensions but one are negligible e.g a beam or a pole.

Assumptions:
1. Mass is concentrated along a line
2. No thickness
3. Rigid (doesn’t bend/buckle)

Question 2

Lamina

Answer 2

Object with area but negligible thickness, like a sheet of paper.

Assumptions: Mass is distributed across a flat surface.

Question 3

Uniform body

Answer 3

Mass is distributed evenly.

Assumptions: mass of the object is concentrated at a single point at the geometrical centre of the object - the centre of mass.

Question 4

Mass of the object

Answer 4

Mass of the object is small compared to other masses (like a string or a pulley)

Assumptions:
1. treated as having 0 mass
2. tension the same at both ends of the light string.

Question 5

Inextensible string

Answer 5

A string that does not stretch under load.

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

Question 6

Smooth surface

Answer 6

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

Question 7

Rough surface

Answer 7

Means not a smooth surface

Assumption: objects in contact with the surface experience a frictional force if they are moving/acted upon by a force.

Question 8

Wire

Answer 8

Rigid thin length of metal.

Assumption: treated as one-dimensional.