AS Level Physics Key Terms

SI Unit For Distance

Metres (m)

SI Unit For Time

Seconds (s)

SI Unit For Mass

Kilograms (kg)

SI Unit For Current

Amperes (A)

SI Unit For Amount of Substance

Moles (mol)

SI Unit For Temperature

Kelvin (K)

SI Unit for Luminous Intensity

Candelas (cd)

Kilo (k) value

10^3

How to convert to kilo

Divide by 10^3

Mega (M) value

10^6

How to convert to mega

Divide by 10^6

Giga (G) value

10^9

How to convert to giga

Divide by 10^9

Tera (T) value

10^12

How to convert to tera

Divide by 10^12

Peta (P) value

10^15

How to convert to peta

Divide by 10^15

Milli (m) value

10^-3

How to convert to milli

Multiply by 10^3

Micro (µ) value

10^-6

How to convert to micro

Multiply by 10^6

Nano (n) value

10^-9

How to convert to nano

Multiply by 10^9

Pico (p) value

10^-12

How to convert to pico

Multiply by 10^12

Femto (f) value

10^-15

How to convert to femto

Multiply by 10^15

Define uncertainty

Estimate of difference between reading & true value of measured quantity. Estimate of spread of values around measured quantity where true value will be found

Define absolute uncertainty

Possible difference from true value given as fixed number in measurement's units

Percentage uncertainty

Possible difference from true value given as percentage of measurement

When adding/subtracting measurements…

…add absolute uncertainties

When multiplying/dividing measurements…

…add percentage uncertainties

When raising measurements to a power…

…multiply percentage uncertainty by power

Define random error

Error which causes reading to vary around mean value unpredictably between readings

Define systematic error

Error that causes readings to differ from true value by consistent amounts

Define zero error

Error where measuring instrument reads non-zero output when there is no input

Define accuracy

How close a measured quantity is to true value

Define precision

The smallest change in value measured by instrument/operator. How close measurements are to one another.

Define displacement

Change in position of an object

Define velocity

Speed in a given direction

Define acceleration

Rate of change of velocity

Velocity equation

v = Δs/Δt

Acceleration equation

a = Δv/Δt

Shape of displacement-time graphs for constant velocity, constant acceleration and increasing acceleration

Constant velocity: Straight diagonal line
Constant acceleration: Gradually curving line
Increasing acceleration: Steeply curving line

Shape of velocity-time graphs for constant velocity, constant acceleration and increasing acceleration

Constant velocity: Straight horizontal line
Constant acceleration: Straight diagonal line
Increasing acceleration: Gradually curving line

Shape of acceleration-time graphs for constant velocity, constant acceleration and increasing acceleration

Constant velocity: Empty graph
Constant acceleration: Straight horizontal line
Increasing acceleration: Straight diagonal line

How to find velocity from displacement-time graph

Calculate the gradient

How to find displacement from velocity-time graph

Find area under the graph

How to find acceleration from velocity-time graph

Calculate the gradient

How to find change in velocity from acceleration-time graph

Find area under the graph

Deriving v = u + at

Gradient of velocity-time graph = acceleration = Δy/Δx = Δv/Δt
a = v-u/t
at = v - u
v = u + at

Deriving s = 1/2(u+v)t

Average velocity = u+v/2
s = vt
s = 1/2(u+v)t

s = ut + 1/2at^2

v = u + at
s = 1/2(u+v)t
s = 1/2(u+u+at)t
s = 2ut/2 + at^2/2
s = ut + 1/2at^2

Deriving v^2 = u^2 + 2as

v = u + at
t = v - u/a
s = v + u/2 x t
s = v + u/2 x v - u/a
s = v^2 - u^2/2a
2as = v^2 - u^2
v^2 = u^2 + 2as

Linear Momentum

Product of an object's mass and velocity, with its direction always being the same as the direction of velocity

Law of Conservation of Momentum

Total momentum of an isolated system of interacting bodies remains constant, provided there are no resultant external forces e.g. friction

Force

Rate of change of momentum

Impulse

The product of a force and the time during which the force is applied

Mass

A measure of inertia of a body. The property of a body that resists change in motion

Weight

The force due to a gravitational field

What is conserved in an inelastic collision?

Total momentum of a system is conserved, but the total kinetic energy is not conserved. Speed before impact is not equal to speed after impact

What is conserved in an elastic collision?

Total momentum and total kinetic energy of a system is conserved. Relative speed of approach is equal to the relative speed of separation

Newton's 1st Law

A body remains at rest or constant velocity unless acted on by a resultant force

Newton's 2nd Law

The resultant force is proportional to the rate of change of momentum

Newton's Third Law

If one body exerts a force on another, it will experience a force by the other body, which is equal in magnitude and opposite in direction. Both forces are of the same kind

Centre of Gravity

The point on an object at which the entire weight of the body seemingly acts

Equilibrium

Net/resultant force and moment is zero

Moment/Torque

Product of the force and the perpendicular distance to the pivot

Principle of Moments

Sum of clockwise moments about a point equals sum of anticlockwise moments about the same point

Torque of a Couple

Product of one of the forces and perpendicular distance between forces

Pressure

The perpendicular/normal force applied per unit area

Density

Amount of mass per unit volume of a substance

Upthrust

The resultant force on a submerged object due to pressure difference between the higher pressure at the bottom of the object and the lower pressure at the top of the object immersed in a fluid

Energy

The stored ability to do work

Work Done

Product of a force and the distance moved in the direction of the force

Power

Rate of work done

Efficiency

The fraction of the useful power output obtained from the total power input

Conservation of Energy

Energy cannot be created or destroyed

it may transform into other forms but the total amount of energy stays constant

Gravitational Potential Energy

Energy stored due to height/position of mass in a gravitational field

Kinetic Energy

Energy of an object due to its motion

Potential Energy

Energy stored by an object to do work

Elastic Potential Energy

Energy stored due to deformation or change in shape of an object

Stress

Force per unit cross-sectional area required to stretch a material

Strain

Extension over original length. Ratio of extension to original length.

Young's Modulus

Ratio of stress to strain

Hooke's Law

Force is proportional to extension/compression if limit of proportionality is not exceeded

Ultimate Tensile Strength

The maximum force per original cross-sectional area the object is able to support before it breaks

Ultimate Tensile Stress

The maximum value of stress that an object can sustain before it breaks

Limit of Proportionality

The point beyond which Hooke's Law is no longer obeyed

Elastic Limit

The point beyond which an object will not return to its original length when the force is removed

Brittle Materials

Materials which do not undergo plastic deformation. Force is proportional to extension until it breaks

Ductile Materials

Materials which undergo plastic deformation after a considerable elastic deformation. Initially force is proportional to extension then a large extension for small change in force

Elastic Deformation

Object returns to its original length when load is removed

Plastic Deformation

Object does not return to original shape/length when load is removed

Force-Extension Graph

The area under the graph is work done in stretching a material. For the straight-line portion of the graph, it is a measure of the elastic potential/strain energy stored by the material, if the graph for decreasing loads is the same as that for increasing loads.

Progressive Wave

The transfer or propagation of energy as a result of oscillations/vibrations

Wavelength

Distance moved by wave energy/wavefront during one cycle of the source. Minimum distance between two points with same phase/adjacent crests/troughs

Frequency

Number of oscillations per unit time

Period

The time taken to complete one oscillation/cycle. The time between adjacent wavefronts