Modelling In Mechanics Flashcards
Particle
Dimensions of the object are negligible
The mass of the object is concentrated at a single point Rotational forces can be ignored
Air resistance can be ignored
Rod
All dimensions but one are negligible, like a pole or beam Mass in concentrated along a line
No thickness
A rigid body (does not bend)
Lamina
Object with area but negligible thickness, like a sheet of paper
Mass is distributed across a flat surface
Uniform Body
Mass of the object is concentrated at a single point at the centre of body – the centre of mass
Light Object
The mass of the object is small compared to other masses, like string or a pulley
Treat object as having zero mass
Tension is the same at both ends of a light string
Inextensible String
A string that does not stretch
Acceleration is the same in objects connected by a taut inextensible string
Smooth surface
No frictions between the surface and any object on it
Rough surface
Objects in contact with the surface experience a frictional force
Wire
Rigid thin length of metal
Treated as one-dimensional
Smooth and light pulley
All pulleys are considered smooth and light Pulley has no mass
Tensions is the same on either side of the pulley
Bead
Particle with a hole in it
Moves freely along a wire or string
Tension is the same on either side of the bead
Peg
A support from which a body can be rested Dimensionless and fixed
Can be rough or smooth as specified in question
Air resistance
Experiences as an object moves through the air Usually modelled as being negligible
Gravity
Force of attraction between all objects
Acceleration due to gravity is donated by g
In Maths g = 9.8 m/s2 NOT 9.81
Assume that all objects with mass are attracted towards the Earth
Earth’s gravity is uniform and acts vertically downwards
g is constant and taken as 9.8m/s2 unless otherwise stated
