Modelling assumptions Flashcards
Modelling assumptions
Air resistance
Lamina
Rod
Tension is the same at both ends of a light spring. Here, the mass is very small(regarded as zero).
The surface is smooth
Wire
The surface is rough
Particle
Uniform body
Gravity
Inextensible
Air resistance
The friction an object experiences as it moves through space
Lamina
An object with two dimensions(length and width), such as a sheet of metal. Its mass is evenly distributed across a flat surface.
Rod
An object with one dimension(length), such as a pole or a beam. Its mass is distributed along a straight line. It is rigid(does not bend or buckle).
Smooth surface
This assumes there’s no friction between this surface and an object.
Wire
A rigid, thin length of metal, treated as one dimensional, either smooth or rough
Rough surface
This takes into account friction on surfaces
Particles
Where dimensions of the object are negligible/unimportant. Its mass is concentrated at a single point. Air resistance and rotational forces can be ignored.
Uniform body
Its mass is evenly distributed. Its mass is concentrated at the geometrical centre of the body(centre of mass).
Gravity
The force of attraction to the Earth, measured at 9.8m/s2. It is uniform and acts vertically downwards
Inextensible
When an object does not stretch under a load. Acceleration is constant in objects connected by a taut inextensible string.
One improvement to model of motion to make the model more realistic
As velocity increases, rate of acceleration decreases
Assumption for air resistance in model
Usually ignored
Assumption for bead - a particle with a hole in it for threading on a wire or string
Moves freely along a wire or string
Tension is the same on either side of the bead
Assumption for beam- like a pole
Ignore its thickness.
its mass is concentrated along a line.
It doesn’t bend
Assumptipn for gravity
It’s uniform, acts vertically downwards and is about 9.8m/s2 unless stated otherwise.
Assumption for inextensible
It does not stretch
Assumption for lamina
It has an area, but ignore its thickness
Assumption for light object
Ignore its mass
Assumption for particle
Assume it has no mass or dimensions
Assumption for peg - a support from which something can hang
Ignore dimensions
Assumption for Rod
Ignore its thickness. Its mass is concentrated along a line. It doesn’t bend
Assumption for Smooth
Ignore any friction
Assumption for Uniform
Its mass is either evenly spread throughout the body or is concentrated at a single point
Assumption for wire
Ignore thickness. Its mass is concentrated along a line. It does not bend
Realistic velocity time graph
Rate of acceleration decreases as velocity increases
