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Articles - Physics Glossary


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*.

Symbol for ammeter

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.

Symbol for cell

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 -273C 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 36 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*.

Symbol for voltmeter

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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