Mechanics Year 1

What does it mean if something is modelled as a particle?

• the dimensions of the object are negligible

• The mass of the object is concentrated at a single point

• Rotational forces/ air resistance can be ignored

What can we assume if the object is on a rough/ smooth surface?

• if the object is on a rough surface we can assume it experiences friction

• If the object is on a smooth surface we can assume there’s no friction

What can we assume if it talks about a smooth/light pulley?

• we can assume there’s no friction because its Smooth, so tension is the same either side of the pulley

• We can assume the pulley has no mass because its light

What does an inextensible string suggest?

• The string does not stretch under load

• So the acceleration is the same in any connected objects

What can we assume about a rod?

• one dimension is negligible like a pole or beam

• Mass is concentrated along the line, rigid

Common assumption with a uniform rod

Assume that the weight acts at the centre / midpoint of the rod