Physic unit 1/2 glossary

absolute zero The coldest possible temperature.

absorbed dose The amount of ionising radiation

absorbed per kilogram of irradiated material,

measured in grays (Gy).

absorption The taking up and storing of energy,

such as radiation, light or sound, without

it being reflected or transmitted. During

absorption the energy may change from one

form into another. When radiation strikes the

electrons in an atom, the electrons move to a

higher orbit or state of excitement by absorption

of the radiation’s energy.

acceleration The rate of change of velocity.

Acceleration is a vector quantity. The SI unit for

acceleration is m s−2.

activity The number of nuclei of a radioactive

substance that decay each second, measured in

becquerels (Bq).

air pressure The force per unit area exerted by

air on an object; related to the density or the

number of particles.

air resistance The retarding force (drag) caused

by collisions between air and moving objects.

alpha particle A particle consisting of two

protons and two neutrons ejected from the

nucleus of a radioactive nuclide.

alternating current In an alternating current

(AC), electrons oscillate backwards and

forwards around a mean position, as opposed to

direct current (DC). Household power supplies

usually operate at 240 V AC.

amplitude The maximum displacement of a

particle from the average or rest position.

angle of incidence The angle an incident ray

makes with the normal to the surface it strikes.

angle of reflection The angle a reflected ray

makes with the normal to the surface it strikes.

Equal to the angle of incidence.

angle of refraction The angle a refracted ray

makes with the normal to the surface as it

travels from one medium to another.

antineutrino A neutral subatomic particle that

interacts very weakly with other matter; the

antimatter particle of neutrino.

antinode Areas in a standing wave where

complete constructive interference is

happening.

artificial transmutation The changing of one

element or isotope into another. This happens

during radioactive decay and during neutron

bombardment in a nuclear reactor.

atomic number The number of protons in a

nucleus.

B

background radiation The low level of ionising

radiation that exists in the environment as a

result of the Earth being radioactive.

beta particle An electron or positron ejected

from the nucleus of a radioactive nuclide.

binding energy Energy required to split a

nucleus into its separate nucleons.

C

centre of mass A single point in an object where

the mass can be considered to be ‘concentrated’

for the purposes of analysing motion.

chain reaction A series of nuclear fissions that

may be controlled or uncontrolled.

charge A property of matter that causes electric

effects. Protons have positive charge, electrons

have negative charge and neutrons have no

charge.

circuit breaker A device that automatically

switches off an excessive current by detecting

the magnetic field associated with it.

collinear Lying on the same straight line.

components The components of a force are two

vectors at right angles to each other that when

added together will be equivalent to the original

force.

compressions Areas of high pressure in a wave.

conduction The movement of energy (such as

heat) from one object to another without the net

movement of particles (atoms or molecules).

conductor A substance, body or system that

readily conducts heat, electricity, sound or light.

conservation of energy The energy in a system

before an interaction is exactly equal to the

energy in the system after the interaction.

conservation of mechanical energy The total

mechanical energy in a system (i.e. the potential

and kinetic energies) remains constant.

conserved When a quantity that exists before an

interaction is exactly equal to the quantity that

exists after the interaction.

constructive interference The process where

two or more waves combine or superpose to

reinforce each other. This occurs where the

displacement of the individual waves is in the

same direction so the amplitude is increased.

contact forces Forces that exist when one object

or material is touching another. Friction, drag

and normal reaction forces are contact forces.

control rod Material, commonly boron, steel or

cadmium, that absorbs neutrons in a nuclear

reactor.

controlled variable A variable that must be kept

constant during an investigation.

convection A process of heat transfer through a

gas or liquid by bulk motion of hotter material

into a cooler region.

conventional current A flow of positive electric

charge. Conventional current is in the opposite

direction to electron flow.

coolant A substance, commonly water, carbon

dioxide or liquid sodium, used to transfer

thermal energy from the core of a nuclear

reactor.

core Part of a nuclear reactor where nuclear

fission occurs and thermal energy is produced.

coulomb The SI unit of charge; 1C is equivalent

to the combined charge of 6.2 Å~ 1018 protons.

crest The maximum positive displacement

reached when particles in a transverse wave are

displaced upwards from the average position, or

resting position.

critical angle For refraction, this is the incident

angle at which total internal reflection occurs.

That is the refracted angle is exactly 90 degrees

from the normal and lies along the interface

between the two media.

critical mass The minimum amount of enriched

fissile material in the shape of a sphere that

leads to a sustained fission reaction.

current The net flow of electric charge. Current

is measured in amperes (A) where 1 A = 1 C s−1.

By convention, electric current is assumed to

flow from positive to negative.

D

daughter nucleus A nucleus on the product side

of nuclear equation that results when a nucleus

undergoes fission or radioactive decay.

decay series A sequence of radioactive decays

that results in the formation of a stable isotope.

dependent variable The variable that

may change in response to a change in

the independent variable. On a graph, the

dependent variable is plotted on the vertical

axis.

destructive interference The process in which

two or more waves combine or superpose to

reduce the amplitude. This occurs where the

displacement of the individual waves is in the

opposite direction.

deuterium An isotope of hydrogen with one

proton and one neutron.

diffract The process affecting light and other

wave forms that causes the wave to spread out

as the wave passes through a narrow aperture or

past an edge.

diffuse Spread out; for example, a wave reflecting

off an irregular surface.

dimension Space can be considered to consist

of three length dimensions. These length

dimensions are arranged at 90 degrees to each

other with their point of intersection being

the origin. The position of an object can be

defined in relation to its position along each

of the three dimensions. Typically, these three

dimensions are labelled x, y and z. However,

up-down, left-right and backward-forward are

also appropriate.

dimensional analysis Using the units in a graph

or formula to check that the derived term is

correct.

direct current In a direct current (DC),

electrons travel in one direction only, as

opposed to alternating current (AC). Batteries

and electric cells provide direct current.

direction conventions Standardised systems

for describing the direction in which an object

is travelling. The use of cardinal points of a

compass (N, S, E and W) is an example of a

direction convention.

displacement An object’s change in position,

relative to its starting position and final position.

Displacement does not consider the route the

object took to change position, only where it

started and where it ended. Displacement is a

vector quantity. It is measured in metres (m)

and given the symbol s.

distance travelled How far an object travels

during a particular motion or journey. Distance

is a scalar value. Direction is not required when

expressing magnitude. It is measured in metres

(m) and given the symbol d.

Doppler effect A change in the observed

frequency of a wave, such as sound or light that

occurs when the source and observer are in

motion relative to each other.

dose equivalent A measure of the biological

damage inflicted on a tissue due to absorption

of a defined quantity of radiation. Dose

equivalent measurements take into account the

nature of the radiation applied. It is measured in

sieverts (Sv).

earth The third wire (usually green or green

and yellow) in electrical devices that acts as

an important safety feature by carrying excess

current due to a device malfunction directly

into the Earth.

echo The reflection of sound from a distant

surface that reaches the ear in more than

0.1 seconds and is therefore heard as a separate

sound to the original sound.

effective resistance A single resistance that

could be used to replace a number of individual

resistors for the purpose of circuit analysis.

efficiency The percentage of energy that is

effectively transformed by a system.

elastic collision Collision in which kinetic

energy is conserved.

electric current The flow of charged particles.

electric shock Also known as electrocution, in

which excess electricity flows into the human

body due to a device malfunction or electrical

accident.

electrical potential energy Potential energy

due to the separation of charge in part of an

electric circuit.

electricity A form of energy resulting from the

existence of charged particles (electrons or

protons). Electricity is fuelled by the attraction

of particles with opposite charges and the

repulsion of particles with the same charge.

electromagnetic radiation A wide range

of frequencies (or wavelengths) that can be

created by accelerating charges, which result in

a rapidly changing magnetic field and electric

field travelling out from the source.

electromagnetic spectrum The entire range

of electromagnetic radiation. Consists of radio

waves, microwaves, infrared radiation, visible

light, ultraviolet, X-rays and gamma rays. In a

vacuum, all electromagnetic radiation travels at

3.0 Å~ 108 m s−1.

electron A negatively charged particle in the

outer region of an atom; it can move from

one object to another, creating an electrostatic

charge. When electrons move in a conductor,

they constitute an electric current.

electron flow The net flow of electrons.

Although electric current is assumed to flow

from positive to negative, electrons physically

move from negative to positive.

electronvolt (eV) A small unit of energy. One

electronvolt (1 eV) is the energy an electron

would gain when accelerated across a potential

difference of one volt: 1 eV = 1.6 Å~ 10−19 J.

electrostatic force A force that acts between

charged particles and can act over relatively

large distances.

elementary charge The magnitude of the charge

on an electron or proton: e = 1.6 Å~ 10−19 C.

emit Give out. Energy can be emitted in the form

of heat, light, radio waves etc.

energy An object possesses energy if it has the

ability to do work. Energy takes many forms, for

example kinetic energy and potential energy.

evaporation The changing of a liquid into a

gas, often under the influence of heat (At a

temperature below the boiling point).

Ff

ast breeder reactor A fast breeder reactor is a

nuclear fission reactor in which some neutrons

from the fission of uranium-235 are absorbed

by non-fissile uranium-238. The non-fissile

U-238 usually makes up about 99.3% of nuclear

fuel, while the U-235 makes up about 0.7%,

however in fast breeder reactors the fuel is

enriched until the percentage of fissile U-235 is

between 15 and 30%. After absorbing a neutron

the U-238 undergoes two beta-minus decays in

a relatively short period of time to transmutate

into the fissile Plutonium-239 isotope. The

Pu-239 can be extracted and used as a fuel for

another nuclear fission reactor. The term `fast'

in the name refers to the fact that fast neutrons

are more effectively absorbed by U-238 than

slow neutrons, and so a moderator is not

required. This would normally be a problem for

normal fission reactors, however at the level of

enrichment of the fuel in fast breeder reactors

the absorption of fast neutrons by U-235

will still occur at a sufficient rate to sustain

both the chain reaction and the plutonium

production process.

first harmonic Also known as the fundamental;

the longest resonant wavelength in a string or a

pipe. For a string or a pipe open at both ends,

it is half a wavelength and consists of a node

in pressure at each end and an antinode in

the middle. For a pipe closed at one end it is a

quarter of a wavelength and consists of a node

in pressure at the open end and an antinode at

the closed end.

fissile Capable of undergoing nuclear fission

after capturing low-energy neutrons.

fission When a nucleus splits into two or more

pieces, usually after bombardment by neutrons.

fission fragments Nuclides formed during

nuclear fission; these are usually radioactive.

forcing frequency The frequency of the force

applied to an oscillating substance or object

force A vector quantity which measures the

magnitude and direction of a push or a pull.

It is measured in newtons (N).

free fall A motion whereby gravity is the only force

acting on a body.

frequency A measure of the rate at which

something occurs, for example the number of

vibrations or cycles that are completed per second

or the number of complete waves that pass a

given point per second. Measured in hertz (Hz).

fuel rod Long, thin rod of enriched uranium

used in a nuclear reactor.

fundamental The lowest and simplest form of

vibration, with one antinode.

fuse A circuit device that melts when too much

current flows through it, breaking the circuit

in the process and protecting the other circuit

components.

fusion A process taking place inside stars in

which small nuclei are forced together to make

larger nuclei. Energy is released in the process.

G

gamma ray High-energy electromagnetic

radiation ejected from the nucleus of a

radioactive nuclide.

Geiger counter A device for measuring

radioactive emissions.

gravitational potential energy Energy

available to an object due to its position in a

gravitational field. Measured in joules (J).

H

half-life The time taken for half of the nuclei of a

radioactive isotope to decay.

harmonic The resonant frequencies produced

when standing waves are formed in a string or

air column.

heat The energy transferred from a hotter object

to a cooler one that increases the kinetic and/

or potential energy of the particles in the cooler

object.

heat exchanger Part of a nuclear reactor where

heat drawn from the reactor core is used to turn

water into steam.

heavy water Water that has a higher than normal

proportion of water molecules that contain

deuterium.

I

impulse The change in momentum of an object

is also called the impulse of an object. The

impulse is calculated by the final momentum

minus the initial momentum.

incident Arriving at or striking a surface, especially

a beam of light or radiation, or particles.

independent variable The variable that is

selected and deliberately changed by the

researcher. On a graph, the independent

variable is plotted on the horizontal axis.

inelastic collision Collision in which kinetic

energy is not conserved.

inertia A property of an object, related to its

mass, that opposes changes in motion.

insulator A material or an object that does not

easily allow heat, electricity, light or sound to

pass through it. Air, cloth and rubber are good

electrical insulators; feathers and wool are good

thermal insulators.

intensity A measurement of the energy

transmitted by a wave or radiation, given by the

square of the amplitude.

internal energy The total kinetic and potential

energy of the particles within a substance.

inverse square law Relationship between two

variables where one is proportional to the

reciprocal of the square of the other.

ion Atom of a chemical element in which the

number of electrons and protons is not equal

and therefore the atom is electrically charged.

If extra electrons are present, the ion has a

negative charge. If electrons are missing, the ion

has a positive charge.

ionising ability The ability of particles or

radiation to ionise matter.

ionising radiation Radiation with enough

energy to alter the molecular structure of

matter by displacing one or more electrons

from an atom and thus creating electrically

charged ions.

isotope Atoms with the same number of protons

but with different numbers of neutrons.

J

junction A point in an electric circuit from which

current can flow into or out of from more than

one direction.

K

kelvin An absolute temperature scale based on

the triple point of water.

kilowatt hour (kW h) Unit of energy equivalent

to 3.6 megajoules. The equivalent amount of

energy as a 1000 W device turned on for one

hour. It is the unit of measure of electricity

usage that is measured by electricity meters and

appears on electricity bills.

kinetic energy The energy of a moving body,

measured in joules (J).

kinetic particle model A model that states that

the small particles (atoms or molecules) that

make up all matter have kinetic energy, which

means that all particles are in constant motion,

even in solids.

L

latent heat The ‘hidden’ energy used to

change the state of a substance at the same

temperature, i.e. the energy is not seen as a

change in temperature.

latent heat of fusion The energy required to

change 1 kg of solid to a liquid at its melting

point.

latent heat of vaporisation The energy

required to change 1 kg of liquid to a gas at its

boiling point.

longitudinal A longitudinal wave is one in which

the vibration of the particles within the medium

are parallel to the direction of energy flow of

the wave.

M

magnitude The size or extent of something, with

no need for direction. In physics, this is usually

a quantitative measure expressed as a number

of a standard unit.

mass An amount of matter. One kilogram of

mass is equal to the amount comprising the

standard kilogram cylinder of platinum–iridium.

Mass can be defined by the amount of matter

that would result in an acceleration of 1 m s−2

when a force of 1 N is applied in a frictionless

environment.

mass number The number of nucleons (protons

and neutrons) in a nucleus.

mean The average value that is calculated by

taking the sum of all values and then dividing by

the total number of values.

mechanical energy The energy that a body

possesses due to its position or motion. Kinetic

energy, gravitational energy and elastic potential

energy are all forms of mechanical energy.

mechanical wave A wave that transfers energy

through a medium.

median The middle piece of data when a data set

is listed in order.

medium The material or substance through

which a mechanical wave moves.

metal Material in which some of the electrons

are only loosely attracted to their atomic nuclei.

The properties of metals include: high strength,

good electrical and thermal conductivity, lustre,

malleability and ductility.

mode The most common piece of data in a

data set.

moderator A material, usually graphite or water,

that slows neutrons in a nuclear reactor.

momentum The product of an object’s mass and

velocity. Objects with larger momentum require

a larger force to stop them in the same time that

an object with smaller momentum takes to stop.

It is given by the equation p = mv.

N

natural frequency The specific frequency at

which an object will tend to vibrate.

net charge When the number of positive and

negative charges in an object is not balanced.

net force The vector sum of all the individual

forces acting on a body.

neutral No electric charge, or a situation in

which positive and negative charges are

balanced.

neutron An uncharged subatomic particle.

newton SI unit of force. One newton (1 N) is

defined as the force required to make a mass of

1 kg accelerate at 1 kg m s−2.

Newton’s first law States that an object

will maintain a constant velocity unless an

unbalanced, external force acts on it.

Newton’s second law States that force is equal

to the rate of change of momentum. This can

be processed mathematically to: the acceleration

of an object is directly proportional to the force

on the object and inversely proportional to the

mass of the object.

Newton’s third law States that for every

action (force), there is an equal and opposite

reaction (force).

node Areas in a standing wave where complete

destructive interference is occurring and the

two waves totally cancel each other out.

non-contact forces Forces that act at a distance

and do not require the bodies to actually touch

each other. Strong nuclear, weak nuclear,

gravitational and electromagnetic forces are

non-contact forces.

non-ionising radiation Radiation that does

not have enough energy to break the molecular

bonds within molecules and to alter the number

of electrons in an atom. Lower forms of energy

in the electromagnetic spectrum such as radio

waves, microwaves, visible light and UVA

radiation are non-ionising.

non-metal Material in which all of the electrons

are strongly attracted to their atomic nuclei.

non-ohmic Not behaving according to Ohm’s

law; resistance changes depending on the

potential difference.

normal An imaginary line at 90°, i.e.

perpendicular, to a surface.

nuclear transmutation The changing of one

element into another.

nucleon A particle located in the nucleus of an

atom.

nucleus The central part of an atom.

nuclide The range of atomic nuclei associated

with a particular atom, which is defined by its

atomic number, and the various isotopes of that

atom as identified by the mass number.

O

ohmic A resistor that follow’s Ohm’s law; i.e.

has a linear relationship between the current it

draws and the potential difference across it.

oscillate The movement of particles about their

average position in a regular, repetitive or

periodic pattern.

outlier A value that lies outside the main group

of data of which it is a part. Outliers in data

could be caused by errors in the experiment.

overload When an unsafe amount of current

flows through a wire; for example, when too

many electrical appliances are connected to the

same power point.

overtone A harmonic (resonant frequency) that

is higher than the natural frequency.

P

parallel circuit A circuit that contains junctions;

the current drawn from the battery, cell or

electricity supply splits before it reaches the

components and re-joins afterwards.

parent nucleus A nucleus on the reactant side

of a nuclear equation that when struck by a

neutron undergoes fission or simply decays by

natural means.

particle displacement The measure of the

distance a particle moves about its equilibrium

position during the propagation of a wave. In

a longitudinal wave this motion is parallel to

the direction of propagation of the wave. In

a transverse wave it is perpendicular to the

direction of travel.

passive heating Energy efficient design that lead

to little or no mechanical heating requirements

in a building.

penetrating ability A measure of how easily

radiation passes through matter.

period The time interval for one vibration or

cycle to be completed.

personal protective equipment (PPE)

Equipment such as safety glasses and disposable

gloves used to protect people working in the

laboratory.

phase When two or more waves of the same

wavelength and amplitude exactly line up.

plane wave A wave that has a straight wave front.

position The location of an object with respect to

a reference point. Position is a vector quantity.

positron The antimatter pair of the electron. This

means it shares the same mass as an electron

but has opposite properties like electromagnetic

charge and spin.

potential difference The difference in electric

potential between two points in a circuit;

measured by a voltmeter when placed across a

circuit. A battery creates the potential difference

across a circuit, which drives the current.

potential energy Energy that can be considered

to be ‘stored’ within the field due to an object’s

position within the field, composition or

molecular arrangement.

power The rate at which work is done; a scalar

quantity measured in watts (W).

proton A positively charged subatomic particle.

pulse A single movement, vibration or

undulation.

Q

qualitative variable A variable that can be

observed but not measured.

quality factor The number used to indicate the

weighting of the biological impact of radiation.

quantitative variable A variable that can be

measured.

R

radiation Rays or particles that carry energy.

Also, the process by which energy is emitted

by an object or system, transmitted through an

intervening medium or space, and absorbed by

another object or system.

radiation shield A thick concrete wall that

prevents neutrons escaping from a nuclear

reactor.

radioactive Something that spontaneously emits

radiation in the form of alpha particles, beta

particles and gamma rays.

radioisotope An isotope of a chemical element

that emits radioactivity due to its unstable

combination of neutrons and protons in the

nucleus.

random error An error in measurement that

occurs in an unpredictable manner.

rarefaction An area of decreased pressure within

a longitudinal sound wave.

raw data The actual measurements taken directly

during an investigation without being processed

in any way.

ray A line drawn perpendicular to a wave front

and in the direction the wave is moving. (Also a

narrow beam of light.)

reflection The change of direction of a wave as it

strikes a surface and is bounced back.

refraction The bending of the direction of travel

of a ray of light, sound or other wave as it enters

a medium of differing refractive index (optical

density).

reliability The consistency of the results

obtained from an experiment or collection

of data. Reliable results are also repeatable,

meaning another scientist performing the same

analysis will come up with the same results.

residual current device (RCD) A device that

can detect a difference in the active and neutral

wires and switch off current in dangerous

situations to help prevent electrocution.

resistance A measure of how much an object

or material resists the flow of current; the ratio

of the potential difference across a circuit

component and the current flowing through it:

R = V/I. Resistance is measured in ohms (Ω).

resistor A circuit component, often used to

control the amount of current in a circuit by

providing a constant resistance. Resistors are

ohmic conductors, i.e. they obey Ohm’s law.

resonance The state of a system in which an

abnormally large vibration is produced in

response to an external vibration. Resonance

occurs when the frequency of the vibration is

the same, or nearly the same, as the natural

vibration frequency of the system.

resonant frequency The natural frequency at

which an object tends to vibrate.

resultant One vector that is the sum of two or

more vectors.

reverberation This is a reflection of sound from

a nearby surface that reaches the ear in less than

0.1 seconds and combines with the original

sound. It often sounds like a longer sound.

S

scalar A physical quantity that is represented by

magnitude and units only. Mass, time and speed

are examples of scalar quantities.

seismic wave Vibrations within the earth caused

by phenomena such as earthquakes, explosions,

volcanoes and landslides.

series circuit When circuit components are

connected one after another in a continuous

loop so that the same current passes through

each component.

short circuit The situation in which a good

conductor is inadvertently placed across a

battery and an excessive current flows, which

may cause damage.

significant figures The numbers in a

measurement or calculation that convey

meaning and precision.

sinusoidal In the shape of a sine wave.

specific heat capacity The amount of energy

that must be transferred to change the

temperature of 1 kg of material by 1°C or 1K.

speed The ratio of distance travelled to time

taken. Speed is a scalar quantity. The SI unit for

speed is m s−1.

spontaneous transmutation The changing of

one element into another in a natural process

involving radioactive decay.

standing wave Also called a stationary wave,

the periodic disturbance in a medium resulting

from the combination of two waves of equal

frequency and intensity travelling in opposite

directions.

strong nuclear force A short-range but powerful

force of attraction that acts between all the

nucleons in the nucleus. The strong nuclear

force acts on quarks and binds them together

in hadrons. It also acts at larger distances to

bind protons and neutrons together within

atomic nuclei.

subcritical mass A quantity of fissile material

that is too small to sustain a chain reaction.

supercritical mass A quantity of fissile material

that is large enough to sustain a chain reaction.

superposition When two or move waves travel

in a medium, the resulting wave at any moment

is the sum of the displacements associated with

the individual waves.

systematic error An error that is consistent and

will occur again if the investigation is repeated

in the same way.

T

temperature A measure of the average

kinetic energy of the particles in a substance.

Temperature can be measured in degrees

Celsius (°C) or kelvin (K).

thermal equilibrium For two bodies in thermal

contact, the point at which the two reach the

same temperature and there is no further net

transfer of thermal energy.

total internal reflection Occurs when the

angle of incidence exceeds the critical angle for

refraction. Light or waves are reflected back into

the medium; there is no transmission of light.

tracer A radioactive isotope with a short half-life

that is injected into a patient or ingested to

monitor biological processes in the body.

transfer The conversion of energy from one

system to another.

transform To change from one thing to another;

for example, to change energy from electrical

potential energy to kinetic energy.

transmit To cause light, heat, or sound, etc. to

pass through into a medium.

transuranic Elements with atomic numbers

greater than uranium (Z = 92). All of these

elements are unstable and radioactively decay

into lighter elements.

transverse Lying or extending across something.

The vibrations of a transverse wave are at right

angles to the direction of travel of the wave.

travelling wave A wave that travels unimpeded

through a medium and is not confined to a

given space. Every point on the wave would

have maximum displacement at some point

in time. Similarly, each point would also have

minimum displacement at some point.

tritium An isotope of hydrogen with one proton

and two neutrons.

U

uncertainty The description of the range of

data obtained; the maximum variance from

the mean.

units Properties related to physical

measurements. Units can be fundamental

like metres (m), seconds (s) or kilograms

(kg). Units can also be derived by combining

fundamental units; for example metres per

second (m s−1).

V validity The reasonableness of the results

received from an experiment or collection of

data. Valid results meet all the requirements of

the criteria of the scientific method.

variable A factor or condition that can change.

vector A physical quantity that requires

magnitude, units and a direction in order to be

fully defined. Velocity, acceleration and force are

examples of vector quantities.

vector diagram A system of adding vectors

where each vector is drawn head-to-tail, with

the resultant vector drawn from the tail of the

first vector to the head of the last vector.

velocity The ratio of displacement to time taken.

Velocity is a vector quantity. The SI unit for

velocity is m s−1.

vibration A repeated motion.

volatile Liquids with weak surface bonds that

evaporate rapidly.

volt The unit of electrical potential. One volt is

equal to one joule of potential energy given to

one coulomb of charge in a source of potential

difference. The voltage (or the number of volts)

is another name for the potential difference.

voltmeter A device used to measure the electrical

potential difference between two points in a

circuit.

W wave front The set of points reached by a

wave

of vibration at the same instant. Wave fronts

generally form a continuous line or surface.

wavelength The distance between one peak or

crest of a wave of light, heat or other energy

and the next corresponding peak or crest

(symbol: λ).

weight The force of attraction on a body due to

gravity.

work The transfer of energy as a result of the

application of a force; measured by multiplying

the force and the displacement of its point of

application along the line of action. Measured

in joules (J).