Modelling Assumptions Flashcards
what is a particle
dimensions of the object are negligible
what do we assume when modelling a particle
mass of the object is concentrated at a single point
rotational forces and air resistance can be ignored
what is a rod
All dimensions but one are
negligible, like a pole or a beam
what do we assume about a rod
mass is concentrated along a line
no thickness
rigid (does not bend or buckle)
what is a lamina
Object with area but negligible
thickness is like a sheet of paper
what do we assume about a lamina
mass is distributed across a flat surface
what is a uniform body
Mass is distributed evenly
what do we assume about a uniform body
mass of the object is concentrated at a single point at the geometrical centre of the body
the centre of mass
what is a light object
Mass of the object is small compared to other masses, like a string or
a pulley.
what do we assume about a light object
treat object as having zero mass
tension the same at both ends of a light string
what is an inextensible string
A string that does not stretch under load
what do we assume about an inextensible string
acceleration is the same in objects connected by a taut inextensible string
what is a smooth surface
exactly a smooth surface
what do we assume about a smooth surface
assume that there is no friction between the surface and any object on it
what is a rough surface
If a surface is not smooth, it is rough.
what do we assume about a rough surface
objects in contact with the surface experience a frictional force if they are moving or are acted on by a force
what is a wire
Rigid thin length of metal.
what do we assume about a wire
treated as one-dimensional shape
what is a smooth and light pulley
all pulleys you consider will be smooth and light
what do we assume about a smooth and light pulley
pulley has no mass and tension is the same on either side of the pulley
what is a bead
Particle with a hole in it for threading on a wire or string
what do we assume about a bead
moves freely along a wire or string
tension is the same on either side of the bead
what is a peg
A support from which a body can be suspended or rested.
what do we assume about a peg
dimensionless and fixed
can be rough or smooth as specified in question
what is air resistance
Resistance experienced as an object moves through the air.
what do we assume about air resistance
usually modelled as being negligible
what is gravity
Force of attraction between all objects.
Acceleration due to gravity is denoted by g.
what do we assume about gravity
Assume that 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
