Modelling Assumptions

Question 1

Particle (Dimensions of the objects are negligible.)

Answer 1

Mass of the object is concentrated at a single point, rotational forces and air resistance can be ignored.

Question 2

Rod ( All dimensions but one of the object are negligible, like a pole or a beam)

Answer 2

Mass is concentrated along a line, no thickness, rigid (does not bend or buckle)

Question 3

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

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. ( the centre of Mass)

Question 5

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

Answer 5

Treat object as having zero Mass, tension the same at both ends of a light string

Question 6

In extensible string ( a string that does not stretch under load.)

Answer 6

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

Question 7

Smooth surface

Answer 7

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

Question 8

Rough surface

Answer 8

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

Question 9

Wire ( rigid thin length of metal)

Answer 9

Treated as one dimensional

Question 10

Smooth and light pulley ( all pulleys you consider will be smooth or light)

Answer 10

Pulley has no Mass, tension is the same on either side of the pulley

Question 11

Bead ( particle with a hole in for threading on a wire or string)

Answer 11

Moves freely along a wire or string, tension is the same on either side of the bead.

Question 12

Peg ( a support from which a body can be suspended or rested)

Answer 12

Dimensionless and fixed, can be rough or smooth as specified in question

Question 13

Air resistance( resistance experiences as an object moves through the air)

Answer 13

Usually modelled as negligible

Question 14

Gravity ( force of attraction between all objects. Acceleration due to gravity is denoted by g.)

Answer 14

Assume that all objects with Mass are attracted towards the earth, earths gravity is uniform and acts vertically downwards, g is constant and is take as 9.8ms^-2 unless otherwise stated in the question