Modelling Asumptions

Question 1

Particle=dimensions of the object are negligible

Answer 1

• mass of the object is concentrated at a single point

- rotational forces abs air resistance can be ignored

Question 2

Rod=all dimensions but one are negligible

Answer 2

• mass is concentrated along a line
• no thickness
• rigid doesn’t bend

Question 3

Lamina=object with area bu negligible thickness

Answer 3

-mass is distributed across a flat surface

Question 4

Uniform body=mass is distributed evenly

Answer 4

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

Question 5

Inextensible string=doesn’t stretch under load

Answer 5

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

Question 6

Smooth surface

Answer 6

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

Question 7

Rough surface

Answer 7

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

Question 8

Wire=rigid thin length of metal

Answer 8

Treated as one dimensional

Question 9

Smooth and light pulley

Answer 9

• pulley has no mass

- tension is the same in either side of the pulley

Question 10

Bead=particle with a hole in it for threading string or wire

Answer 10

• moves freely along the wire or string

- tension is the same either side of the bead

Question 11

Peg=support from which a body can be suspended or rested

Answer 11

• dimensionless and fixed

- can be rough or smooth as specified in the question

Question 12

Air resistance=resistance experienced as an object moves through the air

Answer 12

Usually modelled as negligible

Question 13

Gravity=force of attraction between all objects g=9.8ms-2 as acceleration

Answer 13

• all objects with mass are attracted towards the earth
• earths gravity is uniform and acts vertically downwards
• g is constant and is taken as 9.8 unless otherwise stated