mechanics Flashcards
particle (model)
dimensions of the object are negligible
particle (model assumptions)
mass of the object is concentrated at a single point
rotational forces and air resistance can be ignored
rod (model)
all dimensions but one are negligible, like a pole or a beam
rod (model assumptions)
mass is concentrated along a line
no thickness
rigid (does not bend or buckle)
lamina (model)
object with area but negligible thickness, like a sheet of paper
lamina (model assumptions)
mass is distributed across a flat surface
uniform body (model)
mass is distributed evenly
uniform body (model assumptions)
mass of the object is concentrated at a single point at the geometrical centre of the body
light object (model)
mass of the object is small compared to other masses, like a string or a pulley
smooth surface (model assumptions)
assume that there is no friction between the surface and any object on it
rough surface (model)
if a surface is not smooth its rough
wire (model)
rigid thin length of material
wire (model assumption)
treated as one-dimensional
smooth and light pulley (model)
all pulleys you consider will be smooth and light
bead (model)
particle with a hole in it for threading on a wire or string
bead (model assumption)
moves freely along a wire or string
tension is the same on either side of the bead
peg (model)
a support from which a body can be suspended or rested
peg (model assumptions)
dimensionless and fixed
can be rough or smooth as specified in question
air resistance (model)
resistance experienced as an object moves through the air
air resistance (model assumption)
usually modelled as being negilible
gravity (model)
force of attraction between all objects. acceleration due to gravity is denoted by g
gravity (model assumptions
assume that all objects with mass are attracted towards the earth.
earth’s gravity is uniform and acts vertically.
g is constant and is taken as 9.8ms^-2,unless otherwise stated in the question
What is the average velocity formula?
displacement from starting point/time taken
What is the average speed formula?
total distance travelled/time taken
Define an inextensible string?
a string that does not stretch under load.
inextensible string (model assumption)
acceleration is the same in objects connected by a taut inextensible string
light object (model assumption)
treat object as having zero mass
tension is the same at both ends of a light string.
What is Newton’s First Law?
An object at rest will stay at rest and that an object moving with constant velocity will continue to move with constant velocity unless an unbalanced force acts on the object.
What is Newton’s Second Law?
F = ma
What is Newton’s Third Law?
That for every action there’s an equal and opposite reaction.
Define resistance?
The force that opposes the motion of a particle
Define tension?
a force that prevents two objects moving away from each other.
Define thrust?
A force that prevents two objects coming together
What are external forces?
Forces produced by something outside the system.
Define Friction?
A type of resistance force. It’s always exactly the correct size + direction to keep an object stationary
