mechanics modelling assumptions

Question 1

particle assumption

Answer 1

• it has no dimensions and that the mass of the object is concentrated at a single point
• therefore we can ignore effects due to air resistance and rotational effects of forces acting upon it

Question 2

rod assumptions

Answer 2

• Modelling an object as a rod means the mass can be considered to be distributed along a straight line.
• The rod has no thickness (is one dimensional) and does not bend or buckle (is rigid).

Question 3

uniform body assumptions

Answer 3

mass evenly distributed over its entire volume if it is uniform.
- This means it has a centre of mass - the point where the mass of the body is concentrated

Question 4

Light object assumptions

Answer 4

If an object is light we can ignore its mass
- tension is the
same throughout its length and that
- its mass does not need to be considered when
treating the system as a whole

Question 5

Inextensible / inelastic string assumptions

Answer 5

they do not stretch under a load.
- acceleration of both objects are the same

Question 6

smooth surface assumptions

Answer 6

ignore friction

Question 7

if a string is inextensible…

Answer 7

string doesnt stretch, two particles accelerate at the same rate

Question 8

if pulley is smooth

Answer 8

• no friction
• so tension is the same throughout