# Modelling in mechanics

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• MODELLING IN MECHANICS
• gravity
• force of attraction between all objects due to gravity (g).      g is 9.8 m/s^2
• g is constant and is taken as 9.8 unless otherwise stated in the question
• assume that all objects with mass are attracted to the earth
• uniform body
• mass is distributed evenly
• mass of an object is concentrated at a single point; at the geometric centre of the body - the centre of the mass
• rod
• all dimension but one are negligible, like a pole or a beam
• rigid ( doesn't bend or buckle )
• no thickness
• mass is concentrated along a line
• lamia
• object with area but negligible thickness like a sheet of paper
• mass id distributed over a flat surface
• smooth and light pulley
• all pulleys you consider will be a smooth and light pulley
• pulley has no mass
• tension is the same on either side of the pulley
• particle
• dimensions of the object are negligible
• mass of the object is concentrated at a single point
• rotational forces and air resistance an be ignored
• air resistance
• resistance experienced as an object moves through the air
• usually modelled as negligible
• inextensible string
• a sting that does not stretch when under load
• acceleration is the same in objects connected by a taught inextensible string
• wire
• rigid thin length of metal
• treated as one dimension
• light object
• smooth surface
• particle with a hole in it for threading on a wire or string
• tension is the same on either side of the bead
• moves freely along the wire or string
• peg
• mass of the object is small compared to the other masses like a string or a pulley
• tension is same at both ends of the light string
• treat the object as having 0 mass
• light object
• resistance experienced as an object moves through the air
• usually modelled as negligible