8.2 Modelling in Mechanics

Question 1

Air resistance

Answer 1

The friction an object experiences as it moves through space

Question 2

Lamina

Answer 2

An object with 2 dimensions (length & width), such as a sheet of metal.

Its mass is evenly distributed across a flat surface

Question 3

Rod

Answer 3

An object with one dimension (length), such as a pole or a beam.

Its mass is distributed along a straight line. It is rigid (does not bend or buckle)

Question 4

Light string*

Answer 4

Its mass is very small (regarded as 0), such as a string or pulley.

Tension is the same both ends of a light string

Question 5

Smooth

Answer 5

This assumes there is no friction between this surface & an object

Question 6

Wire

Answer 6

A rigid, thin length of metal, treated as one dimensional, either smooth or rough

Question 7

Rough

Answer 7

This takes into account friction on surfaces

Question 8

Particle*

Answer 8

Dimensions of the object are negligible. Its mass is concentrated at a a single point. Air resistance & rotational forces can be ignored

Question 9

Uniform body

Answer 9

Its mass is evenly distributed. Its mass is concentrated at the geometrical centre of the body (centre of mass)

Question 10

Gravity

Answer 10

The force of attraction to the Earth, measured at 9.8ms^-2. It is uniform & acts vertically downwards

Question 11

Inextensible*

Answer 11

Does not stretch under a load. Acceleration is constant in objects connected by a taut inextensible string