Modelling assumptions

Question 1

particle assumptions

Answer 1

-mass of object is concentrated at a single point
-rotational forces and air resistance can be ignored

Question 2

rod assumptions

Answer 2

-mass is concentrated along a line
-no thickness
-rigid (does not bend or buckle)

Question 3

lamina assumption

Answer 3

-mass is distributed across a flat surface

Question 4

uniform body assumption

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 assumptions

Answer 5

-treat object as having zero mass
-tension the same at both ends of a light string

Question 6

inextensible string assumption

Answer 6

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

Question 7

smooth surface assumption

Answer 7

-assume there is no friction between the surface and any object on it

Question 8

rough surface assumption

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 assumption

Answer 9

-treated a one dimensional

Question 10

smooth and light pulley assumptions

Answer 10

-pulley has no mass
-tension is the same on either side of the pulley

Question 11

bead assumptions

Answer 11

-moves freely along a wire or string
-tension is the same on either side of the bead

Question 12

peg assumptions

Answer 12

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

Question 13

air resistance assumption

Answer 13

-usually modelled as being negligible

Question 14

gravity assumptions

Answer 14

-assume that all objects with mass are attracted towards the Earth
-Earth’s gravity is uniform and acts vertically downwards
-g is a constant and is taken as 9.8 m s-2, unless otherwise stated in the question