# Definitions Physics ```Definitions
Physics
Edco Exploring Science (Revised Edition)
Definitions
1 Acceleration
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The change in speed divided by
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the time taken for the change.
material.
change in speed
acceleration = ------------------------------------------------------------------------time taken for the change
mass
density = -------------------volume
(page 251)
(page 245)
Alternating current Current that constantly
12
changes direction. (page 329)
3
Density The mass of a unit volume of a
Area The amount of surface that covers
Diode A device that allows current to flow in
one direction only. (page 336)
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an object.
Direct current The flow of charge in one
direction only around a circuit. (page 329)
Area of a square or rectangular object =
length &times; width
14
4
Biomass can generate energy from biological
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sources. (page 283)
5
6
Centre of gravity of a body is a point about
Dispersion of light The breaking up of white
light into its spectrum colours. (page 302)
(page 238)
Echo The reflection of sound is familiar to us
as the echo. (page 311)
16
Electric current The movement of charge
which the turning effects due to gravity are
through a material. The number of electrons
balanced. The weight of the body seems to
that pass a point in a second gives a measure
be concentrated at this point. (page 264)
of the size of the current. (page 321)
Change of state When material changes its
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Electrical charge Bodies become charged by
state energy is taken in (absorbed) or given
the gain or loss of electrons. A body is
out (released). (page 293)
positively charged if it loses electrons. A body
is negatively charged if it gains electrons.
7
Conductors (of electricity) A conductor allows
(page 320)
a charge to move. (page 320)
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8
Conduction (of heat) The transfer of heat
Electromotive force The pull on the electrons
in a circuit. Also called the voltage. (page 323)
through a substance without any overall
movement of the substance itself. Metals are
good conductors of heat. (page 295)
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Energy The ability to do work. Energy is
neither created nor destroyed but can be
converted from one form to another.
9
Convection The transfer of heat through
(page 279)
liquids and gases by the mass movement of
particles. (page 295)
10
Decibel The unit of sound level. (page 311)
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Physics
Edco Exploring Science (Revised Edition)
Definitions
20
Flotation The capacity to float. A solid will
30
Kilowatt hour The unit that measures the
float in a liquid if the solid is less dense than
amount of energy provided when 1 kilowatt
the liquid. It will sink if it is more dense than
of power is used for one hour. (page 331)
the liquid. (page 247)
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21
Force The concept used to describe the cause
Length The straight-line distance between
two points. (page 237)
of motion or a change in the motion of a
body. The unit used to measure force is called
32
Lever A rigid body that can rotate about a
the newton and has the symbol N.
fulcrum. (page 266)
mass
force = ---------------------------------acceleration
Law of the lever: when a lever is balanced,
(page 257)
equals the sum of the anti-clockwise turning
the sum of the clockwise turning effects
effects. (page 268)
22
Friction A force that opposes the motion of a
body when it is in contact with another.
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(page 259)
Light-dependent resistor (LDR) A variable
resistor whose resistance changes with the
amount of light that falls on it. (page 338)
23
Geothermal energy comes from the heat in
the earth beneath the planet’s surface.
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(page 283)
Light-emitting diode (LED) A diode that gives
out light when current passes through it.
(page 338)
24
Heat A form of energy that moves from
hotter bodies to colder ones. (page 294)
35
Luminous and non-luminous bodies A
luminous body creates its own light. A non-
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Hooke’s Law: The extension of an elastic
luminous body reflects light. (page 301)
material is directly proportional to the
applied force producing the extension.
36
(page 261)
Magnetic field The space around a magnet in
which a magnetic force can be detected.
(page 316)
26
Hydro-electricity Energy from the potential
and kinetic energy of water. (page 281)
37
Magnetic force can be attractive or repulsive.
Like poles repel each other and unlike poles
27
Insulator (of electricity) An insulator holds a
attract each other. (page 314)
charge. (page 320)
38
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Insulator (of heat) An insulator does not
Mass The quantity of matter in a body.
(page 241)
allow heat to travel through it easily.
(page 297)
39
Newton The unit of force. Its symbol is N.
(page 257)
29
Joule The unit of work or energy = Newtons
&times; metres (Nm). (page 278)
2
Physics
Edco Exploring Science (Revised Edition)
Definitions
40
Nuclear energy Energy from making (fusion)
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or breaking (fission) nuclear bonds. (page 281)
Static electricity Electricity that is not flowing
as a current. Charged bodies are said to have
static electricity. (page 320)
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Power The amount of work done in a unit of
time. It is measured in watts.
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circuit. (page 335)
Work
Power = --------------- (page 286)
time
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42
Switch A device for completing or breaking a
Temperature A measure of how hot or cold
an object is. (pages 241 and 291)
Pressure The amount of force acting on a
unit of area. The pressure in a liquid increases
with depth.
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movement of the tides and waves. (page 283)
pressure = force
-------------- (page 270)
area
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43
Tidal and wave energy is generated by the
Time is measured by a basic unit called the
second (symbol s). (page 241)
Radiation The transfer of heat by means of
waves that can travel through a vacuum.
(page 296)
55
Ultrasound Sound of a very high pitch.
(page 312)
44
Refraction of light The bending of light as it
passes from one transparent material to
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direction in which it is moving. (page 254)
another. (page 303)
45
Resistor A component that is used to control
Velocity The speed of a body and the
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Voltage The pull on the electrons in a circuit.
Also called the electromotive force of the
the amount of current flowing in a circuit.
battery. voltage = resistance &times; current or
(page 335)
V = RI (page 323–325)
46
Solar energy Energy from the sun. (page 281)
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47
Volume The amount of space taken up by an
Sound is produced when objects vibrate.
object.
(page 308)
Volume of a cube or rectangular box =
length &times; width &times; height (page 239)
48
Spectrum of light The spectrum of light is
made up of seven major colours: red, orange,
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yellow, green, blue, indigo and violet.
Watt The unit of power. Its symbol is J/s.
(page 286)
(page 302)
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49
Wind energy Energy from the kinetic energy
of the wind. (page 282)
Speed The distance travelled by an object in a
unit of time.
distance
speed = ----------------------- (page 250)
time
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Work is done when a force moves an object.
Work done = Force &times; distance moved
in the direction of the force (page 278)
3
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