Mechanics Chapter 8 Flashcards
Modelling Assumptions:
Particle (2)
Mass of the object is concentrated at a single point
Rotational forces and air resistance can be ignored
Modelling Assumptions:
Rod (3)
Mass is concentrated along a line
No thickness
Rigid - does not bend or buckle
Modelling Assumptions:
Lamina (1)
Mass is distributed across a flat surface
Modelling Assumptions: Uniform Body (1)
Mass of the object is concentrated at a single point at the geometrical centre of the body - the centre of mass
Modelling Assumptions: Light Object (2)
Treat object as having zero mass
Tension the same at both ends of a light string
Modelling Assumptions: Inextensible string (1)
Acceleration is the same in objects connected by a taut inextensible string
Modelling Assumptions: Smooth Surface (1)
There is no friction between the surface and any object on it
Modelling Assumptions: Rough Surface (1)
Objects in contact with the surface experience a frictional force if they are moving or are acted on by a force
Modelling Assumptions:
Wire (1)
Treated as one-dimensional
Modelling Assumptions:
Smooth and Light Pulley (2)
Pulley has no mass
Tension is the same on either side of the pulley
Modelling Assumptions:
Bead (2)
Moves freely along a wire or string
Tension is the same on either side of the bead
Modelling Assumptions:
Peg (2)
Dimensionless and fixed
Can be rough or smooth as specified in question
Modelling Assumptions: Air Resistance (1)
Usually modelled as being negligible
Modelling Assumptions:
Gravity (3)
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 ms^-2 unless otherwise stated in the question
What is a particle?
An object with negligible dimensions
What is a rod?
A pole or beam where all dimensions but one are negligible
What is a lamina?
An object with area but negligible thickness, like a sheet of paper
What is a uniform body?
An object where mass is distributed evenly
What is a light object?
An object with mass that is small compared to other masses, like a string or pulley
What is an inextensible string?
A string that does not stretch under load
What is a rough surface?
A surface that is not smooth
What is a wire?
A rigid, thin length of metal
What is a bead?
A particle with a hole in it for threading on a wire or string
What is a peg?
A support from which a body can be suspended or rested
What is air resistance?
Resistance experienced as an object moves through the air
What is gravity?
The force of attraction between all objects
What is weight?
The gravitational force that acts vertically downwards
What is normal reaction?
A force that acts perpendicular to the surface an object is in contact with
What is friction?
A force that opposes the motion between two rough surfaces
What is tension?
A force acting on an object if a string is pulling it
What is thrust/compression?
The force of an object being pushed (e.g. by a light rod)
What is buoyancy?
The upward force on an object allowing it to float or rise when submerged
What is i?
The horizontal component of a vector
What is j?
The vertical component of a vector
What are all vectors made up of? (2)
Horizontal component (multiple of i) Vertical component (multiple of j)
How is the magnitude of a vector calculated?
Pythagoras’ theorem using the components of a vector
What do parallel vectors have in common?
They are multiples of each other
