Modelling in Mechanics

Question 1

what is the particle model

Answer 1

when the dimensions of the object are negligible

Question 2

what is the rod model

Answer 2

all dimensions but one are negligible

Question 2

what are the modelling assumptions of the particle model

Answer 2

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

Question 3

what are the modelling assumptions of the rod model

Answer 3

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

Question 4

what does the lamina model mean

Answer 4

an object with area but negligible thickness, like a sheet of paper

Question 5

what are the modelling assumptions of lamina

Answer 5

mass is distributed across a flat surface

Question 6

what does the uniform body model mean

Answer 6

mass is distributed evenly

Question 7

what are the modelling assumptions of uniform body

Answer 7

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

Question 8

what does the light object model mean

Answer 8

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

Question 9

what are the modelling assumptions of light object

Answer 9

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

Question 10

what does the inextensible string model mean

Answer 10

A string that does not stretch under load

Question 11

what are the modelling assumptions of inextensible string

Answer 11

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

Question 12

smooth surface modelling assumptions

Answer 12

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

Question 13

what does the rough surface model mean

Answer 13

if a surface is not smooth, it is rough

Question 14

rough surface modelling assumptions

Answer 14

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

Question 15

Wire model meaning

Answer 15

Rigid thin length of metal.

Question 16

Smooth and light pulley model meaning

Answer 16

all pulleys you consider will be smooth and light.

Question 17

wire model assumptions

Answer 17

treated as one-dimensional

Question 18

Smooth and light pulley model assumptions

Answer 18

pulley has no mass

tension is the same on either side of the pulley

Question 19

Bead model meaning

Answer 19

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

Question 20

Bead modelling assumptions

Answer 20

moves freely along a wire or string

tension is the same on either side of the bead

Question 21

Peg model meaning

Answer 21

A support from which a body can be suspended or rested

Question 22

peg model assumptions

Answer 22

dimensionless and fixed

can be rough or smooth as specified in question

Question 23

air resistance model meaning

Answer 23

Resistance experienced as an object moves through the air.

Question 24

air resistance model assumptions

Answer 24

usually modelled as being negligible

Question 25

Gravity model meaning

Answer 25

Force of attraction between all objects. Acceleration due
g = 9.8 ms?
to gravity is denoted by g

Question 26

gravity modelling assmuption

Answer 26

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 9.8 m s-‘, unless otherwise stated in the question