Mechanics AS Chapter 8 Modelling Flashcards

assumptions when modelled as particle

- dimensions of object is negligible
- mass of object is concentrated at one point
- rotational forces and air resistance can be ignored

assumptions when modelled as rod

- all dimensions but one are negligible
- mass is concentrated along a line
- rigid (does not bend)

what is lamina

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

assumptions when modelled as lamina

mass is distributed across a flat surface

assumptions when modelled as uniform body

- mass of object is concentrated at the centre

assumptions when modelled as light object

- treat object as 0 mass
- tension the same at both ends of light string

assumptions when modelled as inextensible string

- string does not stretch
- acceleration is the same in objects connected by a taut extensible string

assumptions when modelled as smooth surface

no friction between surfaces

assumptions when modelled as rough surface

objects experience frictional force

assumptions when modelled as wire

treated as one dimensional

assumptions when modelled as smooth + light pulley
(note there hasn't ever been a question where the pulley is only light or is only smooth, it is usually both smooth and light)

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

assumptions when modelled as bead

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

assumptions made about air resistance

negligible

assumptions made about gravity

- assume all objects attracted to Earth
- earth's gravity is uniform and acts vertically downwards
- g is constant and 9.8

what acts against weight

normal reaction

what acts against the direction of motion when 2 things are in contact

friction

where does tension act towards

it acts in the direction the string is being pulled(stretched) in

what is thrust

The force that propels an object forward

what is buoyancy

The ability of a fluid to exert an upward force on an object placed in it