models and assumptions Flashcards
particle
meaning - an object with negligible dimensions
assumptions - ignore effects of any rotational forces and air resistance
rod
meaning - an object with dimensions that are all negligible apart from one, like a pole or beam
assumptions - mass is concentrated along a line
no thickness
and is rigid (so does not bend or buckle)
lamina
meaning - an object with an area but negligible thickness, like a sheet of paper
assumptions - mass is distributed evenly along a flat surface
uniform body
meaning - the mass is evenly distributed
assumption - that the mass of the object is concentrated along a single point at the geometrical centre of the body - the centre of mass
light object
meaning - an object with mass that is small compared to other masses, like a string or pulley
assumption - treat the mass of the object to be zero
and assume tension to be the same at both ends of a light string
inextensible string
meaning - a string that does not stretch under load
assumption - acceleration is the same in objects connected by a taut inextensible string
smooth surface
meaning - obvious
assumption - assume that there is no friction between the surface of any object on it
rough surface
meaning - if a surface is not smooth , it is rough
assumption - assume there is friction between the surface and any object on it if the object is moving or is acted on by a force
wire
meaning - a rigid thin length of string
assumption - treat as one dimensional
smooth and light pulley
meaning - all pulleys you will consider will be smooth and light
assumption - pulley has no mass
and tension is the same on either side of the pulley
bead
meaning - a particle with a hole in it for threading on a wire or string
assumption - moves freely along a wire or string
tension is the same on either side of the bead
peg
meaning - a support from which a body can be suspended or rested
assumption - dimensionless and fixed
can be rough or smooth as specified in the question
air resistance
meaning - resistance experienced as an object moves through the air
assumption - usually modelled as being negligible, in other words, air resistance can be ignored
gravity
meaning - gravity is the force of attraction between all objects
acceleration due to gravity is denoted by g
g = 9.8 m s ^ -2
assumptions - assume all objects with mass are attracted towards the Earth
Earth’s gravity is uniform and acts vertically downwards
g is constant and is taken as 9.8 m s ^ -2 , unless otherwise stated in the question
try and name all the models, (there are fourteen) if possible, with each meaning and assumption although I will not write the meaning and assumption here
Particle
Rod
Lamina
Uniform Body
Light Object
Inextensible string
Smooth surface
Rough surface
Wire
Smooth and light pulley
Bead
Peg
Air Resistance
Gravity
