Mechanics Y1

• Model

  Particle - Dimensions of the object are negligible.

  Modelling assumptions

  • mass of the object is concentrated at a single point

  • rotational forces and air resistance can be ignored
• Model

  Rod - All dimensions but one are negligible, like a pole or a beam.

  Model assumption

  • mass is concentrated along a line

  • no thickness

  • rigid (does not bend or buckle)
• Model

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

  Model assumption

  • mass is distributed across a flat surface
• Model

  Uniform body - Mass is distributed evenly.

  Model assumption

  • mass of the object is concentrated at a single point at the geometrical centre of the body - the centre of mass
• Model

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

  Model assumption

  • treat object as having zero mass

  • tension the same at both ends of a light string
• Model

  Inextensible string - A string that does not stretch under load.

  Model assumption

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

  Smooth surface

  Model assumption

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

  Rough surface - If a surface is not smooth, it is rough.

  Model assumption

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

  Smooth and light pulley - all pulleys you consider will be smooth and light.

  Model assumption

  • pulley has no mass

  • tension is the same on either side of the pulley