AS Mechanics: 8 Modelling in Mechanics Flashcards
What modelling assumptions can be made in a particle model?
- Mass of the object is concentrated at a single point.
- Rotational forces and air resistance can be ignored.
What modelling assumptions can be made in a rod model?
- Mass is concentrated along a line.
- No thickness.
- Rigid (does not bend or buckle).
What modelling assumptions can be made in a lamina model?
- Mass is distributed across a flat surface.
What modelling assumptions can be made in a uniform body model?
- Mass of the object is concentrated at a single point at the geometrical centre of the body - the centre of mass.
What modelling assumptions can be made in a light object model?
- Treat object as having no mass.
- Tension the same at both ends of a light string.
What modelling assumptions can be made in an inextensible string model?
- Acceleration is the same in objects connected by a taut inextensible string.
What modelling assumptions can be made in a smooth surface model?
- Assume there is no friction between the surface and any object on it.
What modelling assumptions can be made in a rough surface model?
- Objects in contact with the surface experience a frictional force if they are moving or are acted in by a force.
What modelling assumptions can be made in a wire model?
- Treated as one-dimensional.
What modelling assumptions can be made in a smooth and light pulley model?
- Pulley has no mass.
- Tension is the same on either side of the pulley.
What modelling assumptions can be made in a bead model?
- Moves freely along a wire or string.
- Tension is the same on either side of the bead.
What modelling assumptions can be made in a peg model?
- Dimensionless and fixed.
- Can be rough or smooth as specifies in question.
What modelling assumptions can be made in an air resistance model?
- Usually modelled as being negligible.
What modelling assumptions can be made in a gravity model?
- Assume that all objects with mass are attracted towards the earth.
- Earth gravity is uniform and acts vertically downwards.
- g is constant and is takes as 9.8ms⁻² unless otherwise stated in the question.
What is weight?
The force that acts vertically downwards.
What is the normal reaction?
The force which acts perpendicular to a surface when an object is in contact with the surface.
What is friction?
The force which opposes the motion between two rough surfaces.
What is tension?
The force acting on an object being pulled along by a string.
What is thrust/compression?
The force acting on an object being used along using a light rod.
What is buoyancy?
The upwards force on a body that allows it to float/rise when submerged in a liquid.
What is air resistance?
The resistive force that opposes motion.
What is a vector quantity?
A quantity which has both magnitude and direction.
Give examples of vector quantities.
Displacement (m): distance in a particular direction.
Velocity (ms⁻¹): rate of change of displacement.
Acceleration (ms⁻²): rate of change of velocity.
What is a scalar quantity?
A quantity which has only magnitude.
Give examples of scalar quantities.
Distance (m): the measure of length.
Speed (ms⁻¹): the measure of how quickly a body is moving.
Time (s): the measure of ongoing events taking place.
Are scalar and vector quantities positive or negative.
Scalar: always positive.
Vector: either positive or negative.
