Modelling

Question 1

Particle - definition

Answer 1

Dimensions of the object are negligible,.

Question 2

Particle - modelling assumptions

Answer 2

Mass of the object is concentrated at a single point

Rotational forces and air resistance can be ignored

Question 3

Rod - definition

Answer 3

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

Question 4

Rod - modelling assumptions

Answer 4

Mass is concentrated along a line

No thickness

Rigid (no bend or buckle)

Question 5

Lamina - definition

Answer 5

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

Question 6

Lamina - modelling assumption

Answer 6

Mass is distributed across a flat surface

Question 7

Uniform body - definition

Answer 7

Mass is distributed evenly.

Question 8

Uniform body - modelling assumption

Answer 8

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

Question 9

Light object - definition

Answer 9

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

Question 10

Light object - modelling assumptions

Answer 10

Treat object as having zero mass

Tension the same at both ends of a light string

Question 11

Inextensible string - definition

Answer 11

A string that does not stretch under load.

Question 12

Inextensible string - modelling assumption

Answer 12

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

Question 13

Smooth surface - modelling assumption

Answer 13

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

Question 14

Rough surface - definition

Answer 14

If a surface is not smooth, it is rough.

Question 15

Rough surface - modelling assumptions

Answer 15

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

Question 16

Wire - definition

Answer 16

Rigid thin length of metal.

Question 17

Wire - modelling assumption

Answer 17

Treated as one-dimensional

Question 18

Smooth and light pulley - definition

Answer 18

All pulleys you consider will be smooth and light.

Question 19

Smooth and light pulley - modelling assumption

Answer 19

Pulley has no mass

Tension is the same on either side of the pulley

Question 20

Bead - definition

Answer 20

Particle with a hole in it for threading on a wire or string.

Question 21

Bead - modelling assumption

Answer 21

Moves freely along a wire or string

Tension is the same on either side of the bead

Question 22

Peg - definition

Answer 22

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

Question 23

Peg - modelling assumption

Answer 23

Dimensionless and fixed

Can be rough or smooth as specified in the question

Question 24

Air resistance - definition

Answer 24

Resistance experienced as an object moves through the air.

Question 25

Air resistance - modelling assumption

Answer 25

Usually modelled as being negligible

Question 26

Gravity - definition

Answer 26

Force of attraction between all objects.

Question 27

Gravity - modelling assumption

Answer 27

Assume that all objects with mass are attracted towards the Earth

Earth;s gravity is uniform and acts vertically downwards

g is constant and is taken as 9.8g/s², unless otherwise stated in the question.