Mechanics: Modelling Assumptions

Question 1

Particle

Answer 1

Mass of the object is concentrated at one point
Air resistance and rotational forces are ignored

Question 2

Rod

Answer 2

No thickness
Mass is concentrated along a line
Rigid

Question 3

Uniform body

Answer 3

Mass is in the centre

Question 4

Light object

Answer 4

Object has 0 mass
Tension the same at both ends of the light string

Question 5

Inextensible string

Answer 5

Acceleration is the same in objects connected by it

Question 6

Smooth surface

Answer 6

No friction

Question 7

Rough surface

Answer 7

Frictional force is present

Question 8

Wire

Answer 8

One dimensional

Question 9

Smooth and light pulley

Answer 9

Pulley has no mass
Tension is the same on either side of the pulley

Question 10

Bead

Answer 10

Moves freely along a wire or string
Tension is the same on either side of the pulley

Question 11

Peg

Answer 11

Dimensionless and fixed
Can be rough or smooth (described in question)

Question 12

Air resistance

Answer 12

Usually modelled as negligible

Question 13

Gravity

Answer 13

All objects with a mass attracted towards the Earth
Gravity is uniform and acts vertically down
g = 9.8ms^-2