8. Modelling in mechanics Flashcards
What are the assumptions involved with particles?
Mass of the object is concentrated at a single point
Rotational forces and air resistance can be ignored
What are the assumptions involved with a rod?
Mass is concentrated along a line
No thickness
Rigid
What are the assumptions involved with lamina?
Mass is distributed across a flat surface
What are the assumptions involved with 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 are the assumptions involved with a light object?
You treat the object as having zero mass
Tension is the same at both ends of a light string
What are the assumptions involved with inextensible string?
Acceleration is the same in objects connected by a taut, inextensible string
What are the assumptions involved with a smooth surface?
Assume that there is no friction between the surface and any object on it
What are the assumptions involved with 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 are the assumptions involved with a wire?
Treated as one-dimensional
What are the assumptions involved with a pulley?
No mass
Tension is the same on either side of the pulley
No friction on the pulley
What are the assumptions involved with a 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
What are the assumptions involved with a peg?
A support from which a body can be suspended or rested
Dimensionless and fixed
Can be rough or smooth
What are the assumptions involved with air resistance?
Usually deemed to be negligible
What are the assumptions involved with gravity?
Assume all objects are drawn towards the Earth
Earth’s gravity is uniform and acts vertically downward
g is constant and is taken as 9.8 m/s2 unless otherwise stated
What is weight?
The gravitational force of an object acting vertically downwards
What is the normal reaction?
The force acting perpendicular to a surface when an object is in contact with the surface
What is friction?
A force which opposes the motion between two rough surfaces
What is tension?
The force acting on an object when it is being pulled along by a string
What is thrust or compression?
If an object is being pushed along using a light rod, the force acting on the object is called the thrust or compression in the rod
What is buoyancy?
The upward force on a body that allows it to float or rise when submerged in a liquid
What is displacement?
The distance moved in a particular direction
