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absolute zero
Absolute zero is the
theoretical temperature at which atoms stop vibrating. All atoms
have vibrational energy, even in solids, but if we cool them, they
vibrate less. In practice, absolute zero would seem to be impossible to
reach - but we can get to within millionths of a degree of it.
acceleration
Rate
of change in velocity.
If a body increases its speed (the result of a force acting on
it) then it is said to have positive acceleration. See also
deceleration*.
ammeter
A
device for measuring current.
An ammeter is always connected directly into a circuit in
series*
with the components through which the current is flowing. A good ammeter
will have virtually no
resistance*.
ampere
The
unit of electrical current,
normally abbreviated to amp or A. 1 amp is equal to a flow
of 1 coulomb*
of charge*
per second. This translates to the formula, amps = coulombs ÷
seconds.
amplitude
The
maximum
displacement
that an oscillation or wave has from its rest position. A measure of the
energy contained in the motion or wave, large amplitude sounds are
louder; large amplitude light waves are brighter.
anion
A
negatively-charged
ion*.
astronomical unit
An astronomical unit
(AU) is defined as the
average distance between the Earth and the Sun
(approximately 148 million kilometers).
atmosphere
A
layer of gases that envelops
a planet, moon or other celestial body.
atom
The
building blocks of matter.
Once thought to be indivisible
particles*, atoms
are now understood to consist of
electrons*,
protons*
and neutrons*.
battery
A
group of electrical cells connected in
series to provide an
energy source for a
circuit*.
cation
A
positively-charged
ion*.
cell
An
energy source providing an electrical
potential difference between its two terminals
such that a current*
can flow between them. A cell's energy is stored internally as chemicals
that react with each other.
charge (Q)
Electrical charge is
a property or quality that
some
particles*
(and hence bodies) can have
which gives rise to forces of attraction or repulsion between those
particles. Charge is measured in
coulombs* and is
represented by the symbol, Q.
circuit
An electrical circuit
consists of an energy source
connected by conductors to electrical components.
coma
The gas and dust
surrounding the nucleus of a comet..
We see a comet's coma for two reasons. First, because the dust in the
coma reflects sunlight and, second, because sunlight makes the
gas in the coma fluorescent.
conductor
A conductor is a
medium through which an
electric
current*
will flow.
constellation
One
of the 88 named patterns of stars.
For example, the seven brightest stars in the constellation Ursa Major
form the Plough.
coulomb
The
unit of electrical
charge*.
1 coulomb is abbreviated to C.
current (I)
Electrical current is
the flow of
charges*.
In wires, the charges are carried by
electrons*. In
fluids*,
the charges are carried by
ions*. Current is measured in
amperes*
and is represented by the symbol, I.
deceleration
Deceleration is
acceleration*
in the opposite direction to the direction of motion - in other words,
slowing down, or negative acceleration.
displacement
Displacement is
distance moved in a particular
direction. Its unit is m.
electron
One
of the three fundamental
particles*
that make up atoms*.
Electrons are by far the smallest in mass of the three fundamental
particles. They have a negative charge of -1.6 × 10-19 C.
electromotive force (EMF)
See
voltage*.
element (chemical)
A chemical element is
something that cannot be
split into smaller
components through chemical reactions.
element (electric)
An electric element is
a resistor designed to
generate heat (for an
electric fire, say).
energy
Energy enables
something to do physical work
involving the application of a
force.
fission
The
splitting of an atomic nucleus.
This is what is done in nuclear reactors. A neutron is absorbed by the
nucleus (making the nucleus unstable) which then splits into two smaller
nuclei. For nuclei larger than iron, this process releases energy.
fluid
Something that can flow.
Often mistaken as being another word for liquid, in fact both gases and
liquids are fluids.
force
Forces are
pushes and pulls
that make things move or change shape.
frequency
How many times
something occurs in a given time,
normally per second. Frequency is measured in
hertz (Hz)
where 1 Hz = 1 per second.
friction
Friction is
a resisting force
between two surfaces rubbing against each other.
fusion
Fusion is
the joining of atomic nuclei to form a
larger nucleus. Fusion
powers the Sun and stars. It is hoped that we will one day be able to
use the energy from hydrogen fusion to provide for our energy needs.
Fusion only releases energy for nuclei that are smaller than iron.
galaxy
A
very large cluster of stars in space,
normally hundreds of millions of stars, but sometimes as many as
hundreds of billions. Note that the stars in the night sky are all
relatively nearby in our own galaxy, the
Milky Way*.
hemisphere
A hemisphere is
half a sphere or globe.
ion
A
charged
atom* or
molecule*.
A positive ion (or cation) will have lost one or more
electrons*.
A negative ion (or anion) will have gained one or more electrons. Ions
cannot be formed by the loss or gain of
protons*.
ionization
An atom or molecule is
said to be ionized when it has
gained or lost one or more electrons.
If an atom or molecule gains an electron, it is negatively charged (see
anion*);
losing an electron makes it positive (see
cation*).
insulator
An insulator is a
medium through which an
electrical
current*
will not flow.
kelvin
Kelvin is
the absolute temperature scale
and it is measured from
absolute zero*. A
difference in temperature of 1 kelvin is the same as a difference of 1°
C. However, 0 kelvin is approximately -273°C so, on this scale, water
boils at 373 K and freezes at 273 K. Note however that there is no °
symbol used to indicate temperature on the kelvin scale.
kilogram
The
international unit of mass.
A platinum archetype of 1 kilogram of mass is held in Paris.
kWh
The
kilowatt-hour is a unit of energy
It is equivalent to 3·6 megajoules.
light year
The
distance traveled in a year at the speed of light.
magnetism
Magnetism is
a force that can be attractive or
repulsive.
mass
A measure of
the amount of matter
in an object. (Do not confuse mass with
weight*.)
matter
Matter is the
stuff that everything is made from.
Where there is something, there is matter. Otherwise, there is a vacuum.
Milky Way
The Milky Way is
our galaxy.
It contains about 100 billion stars, of which the Sun is just
one. The Milky Way rotates like a large catherine wheel.
molecule
A molecule is the
least amount of a compound
that can exist and still remain a compound.
motor effect
The motor effect is
the result of two things. Firstly, a
current is passed through a conductor:
this forms a magnetic field
around it. Secondly, if an
external magnetic field is
present, the fields will
repel and a force will be
experienced by the conductor. This results in movement.
neutron
One
of the three fundamental
particles*
that make up atoms*.
Neutrons are the largest in mass of the three fundamental particles.
They have no electrical charge.
newton
The
unit of force. 1 newton
(N) is defined as being the force required to give a mass of 1 kg an
acceleration of 1 m/s/s.
Nm2/kg2
Newton metres2
per kilogram2 is
the unit of the Universal
Gravitational Constant. It
is an esoteric unit so it's not one you'll encounter much.
nucleus
pertaining to
an atom:
The centre of an atom.
The nucleus is where
neutrons* and
protons*
are tightly bound. Nuclei are many thousands of times smaller than the
atom itself. For example, if an atom was the size of a football stadium,
the nucleus would be comparable to a pea.
pertaining to a comet:
The solid part
of a comet.
nucleon
Any of two particles
normally found in an atomic nucleus. i.e.
protons and
neutrons.
ohm
The
unit of electrical
resistance*.
Ohm's Law
Ohm's Law quantifies
the relationship
between
voltage*,
resistance*, and
current*
and it most simply translates to volts = amps × ohms.
parallel
In a parallel
electrical circuit, the components
share an energy source
but do not share the same
current.
particle
A particle is a
small piece of something.
plasma
A
white hot gas made only of
ions*.
potential difference
See
voltage*.
power
The amount of
energy
transferred per second. Power is measured in
watts* and is
represented by the symbol, P.
proton
One
of the three fundamental
particles*
that make up atoms. Of the three fundamental particles, protons are the
second largest by mass. They have a positive electrical charge of
+1.6 × 10-19 C.
resistance (R)
Resistance is
the extent to which a
conductor*
hinders the flow of an electric current.
Resistance is measured in
ohms* and is represented by the symbol,
R.
resistor
A resistor is
a circuit component designed to
reduce current.
satellite
A
body that orbits another, larger body.
An artificial satellite is a man-made vessel that orbits a planet
or moon.
series
A series electrical
circuit is a circuit where the components
share the current
flowing around the circuit.
speed
Speed is
the rate of change in distance.
In other words, how quickly something moves through a given distance. It
is normally measured in m/s and its formula is speed =
distance ÷ time. See also
velocity*.
synthetic polymer
A synthetic polymer is
a plastic.
universal gravitational constant, G
G is
a constant required by Newton's Law of
Gravitation. It has
the value 6.67 × 10-11
Nm2/kg2*.
velocity
Velocity is
speed in a stated direction.
The unit of velocity is m/s. Velocity may alternatively be
defined as rate of change in
displacement. The
formula for velocity is velocity = displacement ÷ time. See also
speed.
volt
The
unit of
electromotive force*
or
potential difference*.
voltage (V)
The measure of
energy available to drive a
current*.
Voltage is measured in
volts* and is represented by the
symbol, V.
voltmeter
A
device for measuring
electromotive force*
or
potential difference*.
watt
The
unit of power.
1 watt is defined as the consumption of energy at the rate of 1 joule
per second.
weight
The
force of gravity on a mass.
It is given by the equation, weight = mass × gravity where, on
Earth, gravity = 9.8 N/kg. (Do not confuse weight with
mass*.)
work
Physical work is done
when a force makes something
move. Work is defined by the
formula, work done = force × displacement and its unit is the
newton metre (Nm) or the joule (J).
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