8. Modelling in Mechanics Flashcards
What is a particle?
Dimensions of the object are negligible
What are the modelling assumptions of 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 beam
What are the modelling assumptions of a rod?
Mass is concentrated along a line.
No thickness.
Rigid (does not bend or buckle)
What is a lamina?
An object with area, but negligible thickness, like a sheet of paper.
What are the modelling assumptions of lamina?
Mass is distributed along a flat surface
What is a uniform body?
Mass is distributed evenly
What are the modelling assumptions of a uniform body?
Mass of object is concentrated at a single point at the geometrical centre of the body; its 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 are the modelling assumptions of light objects?
Treat object as having zero mass.
Tension is the same at both ends of a string.
What is an inextensible string?
A string that does not stretch under load
What are the modelling assumptions of an inextensible string?
Acceleration is the same in objects connected by a taut inextensible string
What are the modelling assumptions of a smooth surface?
Assume there is no friction between a surface and the objects on it
What is a rough surface?
If a surface is not smooth, it is rough (duh)
What are the modelling assumptions of 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?
A rigid, thin length of metal
What are the modelling assumptions of a wire?
It is treated as one dimensional
What is a smooth and light pulley?
All pulleys you consider will be smooth and light (yay)
What are the modelling assumptions of smooth and light pulleys?
Pulley has no mass.
Tension is the same either side of the pulley
What is a bead?
A particle with a hole in it for threading on a wire or string
What are the modelling assumptions of 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 are the modelling assumptions of a peg?
Dimensionless and fixed.
Can be rough or smooth as specified.
What is air resistance?
Resistance experienced as an object moves through air.
What are the modelling assumptions of air resistance?
Usually modelled as negligible
What is gravity?
A force of attraction between all objects. Acceleration due to gravity is denoted by g (9.8 ms^-2).
What are the modelling assumptions of gravity?
Assume all objects with mass are attracted towards the Earth.
Earth’s gravity is uniform and acts vertically downwards.
g is constant and taken as 9.8 unless otherwise stated in question.
