Physics AS definitions
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Acceleration
Change in velocity divided by time taken

Speed
Distance travelled divided by time taken

Velocity
Displacement divided by time taken

Displacement
The straight line distance from a reference point in a single specified direction

Vector
Quantities that have both magintude and direction

Scalar
Quantities that are fully defined by by magnitude only

Equilibrium
 No resultant force
 No resultant moment

Moment
Force multiplied by the perpendicular distance from the line of action of the force to the pivot

Principle of moments
Sum of clockwise moments is equal to sum of anticlockwise moments when the object is in equilibrium about the same pivot

Centre of gravity
The single point where the entire weight of a body appears to act

Couple
A pair of equal and opposite forces whose lines of action do not coincide

Torque of a couple
One of the forces multiplied by the perpendicular distance between the forces

Density
Mass divided by volume

Pressure
Force divided by area

Spring constant
Force divided by extension

Hooke's Law
Extension is directly proportional to force provided the elastic limit has not been exceeded

Stress
Force divided by crosssectional area

Strain
Extension divided by original length

Young's Modulus
Tensile stress divided tensile strain

Ductile material
Can be easily and permenantly stretched into thin wires

Elastic
Materials return to their original shape and size when the applied force is removed

Elastic limit
The maximum load up to which the material can regain its original shape and size when the load is removed

Plastic
Material does not return to its original shape and size when the load is removed

Weight
The force of gravity on the mass of a body

Joule
The work done when a force of 1N moves its point of application by 1m in the direction of the force

Kinetic energy
The energy of a body due to movement

Newton
The force needed to give an acceleration of 1ms^{2} to a mass of 1kg

Graviational potential energy
The energy a body has due to its position

Power
Work done divided by time

Work
Force multiplied by distance moved in the direction of the force

Braking distance
Distance travelled from when the brakes are applied until the car comes to a stop

Thinking distance
 Distance travelled during the drivers reaction time before the brakes are applied
 =speed x reaction time

Stopping distance
Thinking distance + braking distance

UTS
The maximum stress a material can withstand before fracture

Strain energy (3 methods)
 Area under Fx graph

Thinking distance
= speed x reaction time

Gradient of displacementtime graph
velocity

Gradient of a velocitytime graph
acceleration

Area under a velocitytime graph
displacement