# Physics Definitions

• Created on: 18-04-13 10:05
Displacement
A vector quantity, describing how far something is from its initial position.
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Velocity
A vector quantity, showing rate of change of displacement.
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Acceleration
A vector quantity, showing rate of change of velocity.
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Speed
A scalar quantity, describing how fast something is moving.
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Newton's First Law
An object remains in a state of rest or constant acceleration unless acted on by a resultant force.
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Newton's Second Law
The rate of change of momentum is proportional to the applied force.
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Newton's Third Law
For every action there is an equal and opposite reaction.
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The conditions necessary for translational equilibrium
The sum of the forces acting on an object must equal zero, i.e. The forces are balanced.
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Linear momentum
The product of an objects mass and velocity.
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Impulse
The rate of change of momentum.
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The law of conservation of momentum
Momentum is always conserved. In a closed system the total momentum at the start is equal to the total momentum at the end.
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The principle of conservation of energy
Energy is always conserved. It may change to another form of energy, but it can't be created or destroyed.
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Power
The rate of energy transfer.
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Efficiency
How well a system converts its input energy into useful output energy.
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The relationship between the Kelvin and Celsius scale
Temperature in K = Temperature in oC + 273
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Thermal Equilibrium
When the heat flowing into an object equals the heat flowing out of it and therefore the temperature remains constant.
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Internal energy
The total kinetic energy of all the molecules in an object plus the potential energy between them.
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One mole
A quantity of atoms, equal to the number of atoms in 12g of carbon-12. This number is the Avagadro constant.
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The constant that defines the number of atoms present in one mole.
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Molar mass
The mass of a given substance divided by the number of moles it contains.
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Specific heat capacity
The energy required to raise the temperature of 1kg of a material by 1K.
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Specific latent heat
The energy required to melt/vaporize 1kg of a material.
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Thermal capacity
The energy required to raise the temperature of a body by a given amount.
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Pressure
The force per unit area.
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The assumptions of the kinetic model of an ideal gas
The gas consists of a large number of particles that move rapidly and randomly and obey Newtonian mechanics. All collisions are elastic. Particles don't attract each other and have negligible volume compared to the space between them.
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Temperature
The apparent "hotness" of "coldness" of a material. A measure of the random kinetic energy of the molecules.
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Amplitude
The maximum disturbance from its undisturbed position.
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Frequency
The number of oscillations per second.
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Wavelength of a travelling wave
The distance between a point on the wave and the next point on the wave with the same displacement.
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Wavelength of a standing wave
Twice the distance between two adjacent nodes.
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Phase difference
The difference between two waves having the same frequency and referenced to the same point in time.
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Simple harmonic motion
When an object is continually accelerating towards an equilibrium position and its acceleration is proportional to its displacement from this equilibrium position.
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Damping
When a wave's amplitude decreases over time.
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Resonance
The state in which the frequency of an externally applied force equals the natural frequency of the system.
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Travelling wave
A wave that transfers energy in its direction of travel.
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Standing wave
A wave formed by the superposition of two waves of the same frequency propagating in opposite directions.
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Snell's Law
The ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant for a given pair of media.
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The principle of superposition
The displacement of a medium at a given point is the sum of the individual displacements of any waves acting at that point.
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Electric potential difference
The work done in moving current between two points in a circuit.
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Electric current
The number of charges that pass a point per unit time.
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Electric resistance
The ratio of the potential difference across a component and the current passing through it.
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emf
The ratio of the power supplied by a power source to the current passing through it.
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electronvolt
The energy required to move an electron across a potential difference of 1V.
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Terminal potential difference
The potential difference across a battery, terminal to terminal.
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Ohm's Law
The potential difference across a component is proportional to the current passing through it.
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Newton's law of gravitation
The force between two objects is proportional to the product of their masses and inversely proportional to the square of the distance between them.
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Coulomb's Law
The force between two charges is proportional to their charges and inversely proportional to the square of their separation.
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Gravitational field strength
The force on a unit point mass in a gravitational field.
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Gravitational potential
The work done in moving a unit point mass from infinity to a point in a gravitational field.
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Electric field strength
The force on a unit point charge in an electric field.
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Electric potential
The work done in moving a unit point charge from infinity to a point in an electric field.
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Magnetic field strength
The force on a current carrying wire in a magnetic field.
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Nucleon number
The total number of particles in an atom's nucleus including protons and neutrons.
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Proton number
The total number of protons in an atom's nucleus.
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Neutron number
The total number of neutrons in an atom's nucleus.
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One twelfth of the mass of an atom of carbon-12.
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Unified atomic mass unit
One twelfth of the mass of an atom of carbon-12.
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Mass defect
The difference in the mass of particles when separate and when joined in a nucleus.
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Binding energy
The energy required to split a nucleus of an atom into its component parts.
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Energy density
The amount of energy contained within 1kg of a fuel.
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Albedo
The reflectivity of the Earth.
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Stefan-Boltzmann Law
The energy emitted per unit time is proportional to: (absolute temperature/temperature in K)^4
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Coefficient of volume expansion
The fractional change in volume per degree change in temperature.
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Surface heat capacity
The energy required to raise the temperature of a unit area of a planet's surface by one degree.
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The first law of thermodynamics
The internal energy of a system is the sum of the thermal energy supplied by/to it and the work done by/to the system.
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The second law of thermodynamics
Entropy is continually increasing in the universe.
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Entropy
The system property defining the degree of disorder in a system.
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The Rayleigh Criterion
For two objects to be just resolved the central minimum of the diffraction pattern of one must line up with the first minimum of the diffraction pattern of the other.
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Brewster's Law
The angle between a reflected ray of polarised light from a transparent surface is at 90o to the refracted ray.
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An induced emf is proportional to the rate of change of magnetic flux linkage through a coil.
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Lenz's Law
An induced emf is induced in order to oppose the motion creating it.
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Capacitance
The ability of a body to store an electrical charge.
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Quantum efficiency
The ratio of the number of electrons emitted to the number of photons incident on a pixel.
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Magnification
The ratio of the length of an object on a CCD to the actual length of the object.
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## Other cards in this set

### Card 2

#### Front

A vector quantity, showing rate of change of displacement.

Velocity

### Card 3

#### Front

A vector quantity, showing rate of change of velocity.

#### Back ### Card 4

#### Front

A scalar quantity, describing how fast something is moving.

#### Back ### Card 5

#### Front

An object remains in a state of rest or constant acceleration unless acted on by a resultant force.

#### Back 