# PH1 Definitions

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Base Quantity
One of 7 quantities from which all other quantities are derived.
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Derived Quantity
A quantity that is formed by the multiplication and/or division of one or more base quantities.
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Scalar Quantity
A quantity with magnitude (size) only.
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Vector Quantity
A quantity with both magnitude and direction.
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Moment
The product of the force and the perpendicular distance from the pivot, to the line of action of the force.
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The Principle of Moments
When an object is in balance, the sum of the moments about any point is equal to zero.
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Centre of Gravity
The point through which the weight of the object appears to act.
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Displacement
Distance moved in a stated direction.
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Mean Speed
Total distance covered divided by total time taken.
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Instantaneous Speed
Rate of change of distance with respect to time at that instant.
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Mean Velocity
Total displacement divided by total time taken.
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Instantaneous Velocity
Rate of change of displacement with respect to time at that instant.
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Mean Acceleration
Total change in velocity divided by total time taken for that change.
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Instantaneous Acceleration
Rate of change of velocity with respect to time at that instant.
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Newton's First Law
Sum of all forces acting on a body equals zero, then, if at rest, the body will remain at rest, and if already moving, the body will continue moving with constant velocity, providing no outside forces are applied.
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Newton's Second Law
Rate of change of momentum is directly proportional to the resultant force applied.
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Newton's Third Law
To every force there is an equal and opposite force.
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Linear Momentum
The product of mass and velocity.
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Principle of Conservation of Momentum
Vector sum of momenta in a system stays constant, provided there are no external forces.
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Elastic Collision
Both kinetic energy and momentum are conserved.
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Inelastic Collision
Kinetic energy is not conserved, but momentum is.
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Energy
The ability to do work.
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Work Done
Transfer of energy and is the product of force and distance moved, in the direction of the force.
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Principle of Conservation of Energy
Energy cannot be made or destroyed, only changed from one form to another.
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GPE
The energy stored in a body due to its change in position (GPE = mgh).
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Elastic Potential Energy
The energy stored in a body due to its change in shape (1/2Fx or 1/2kx2).
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KE
The energy stored in a body due to its speed (1/2mv2).
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Power
Rate of energy transferred.
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Efficiency
Ratio of useful output to input, expressed as a percentage.
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Hooke's Law
Up to the limit of proportionality, the extension is directly proportional to the load applied.
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Stress
Load applied per unit cross-sectional area.
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Strain
The fraction - extension divided by original length (dimensionless).
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Young's Modulus
The fraction - stress divided by strain, and applies within the region of Hooke's Law.
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Crystalline Solids
A solid consisting of randomly arranged crystals. There is short range and long range order.
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Polymeric Solids
Giant macro-molecules with many repeating patterns. There is short range order and long range disorder.
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Amorphous Solids
Atoms arranged so that there is limited short range order and long range disorder.
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Elastic Limit
Maximum load which, if removed, caused no permanent deformation.
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Limit of Proportionality
Maximum load for which the extension is directly proportional to the load.
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Plastic Strain
The strain that results in permanent deformation.
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Permanent deformation
Deformation of a sample that remains once the load has been removed.
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Hysterisis
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The Stellar Spectrum
Characteristic of a star evidenced by its unique pairing of its own continuous emission spectrum and its line absorption spectrum.
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Black Body
A body that will absorb all electromagnetic radiation.
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Wien's Displacement Law
Wavelength of peak emission from a black body is inversely proportional to the absolute temperature.
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Stefan's Law
Total electromagnetic radiation emitted per unit time is directly proportional to the product of surface area and the forth power of the absolute temperature.
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Luminosity
Total energy emitted per unit time in the form of electromagnetic radiation.
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Intensity
Rate of energy received at a point per square metre, or power divided by area radiation is spread over (I = P/(4 pi r2)).
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Quark
Fundamental particles of which the "up" and "down" quarks form members.
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Lepton
Fundamental particles of which the electron, positron neutrino and their associated anti-particles form members.
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Proton
A baryon composed of 2 up quarks and 1 down quark. This gives it a charge of +1 and a baryon number of +1.
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Neutron
A baryon composed of 1 up quark and 2 down quarks. This gives it a charge of 0 and a baryon number of +1.
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Electron
A lepton with little mass and charge of -1. Lepton number of +1. The anti-electron is a positron.
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Positron
A lepton with little mass and charge of +1. Lepton number of -1, and is the anti-particle to an electron.
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Particles consisting of quarks or anti-quarks bound together.
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Baryon
Particles made from 3 quarks. An anti-baryon is made from 3 anti-quarks.
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Meson
Particle made from 2 quarks; a quark and an anti-quark.
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Pion
Unstable mesons that decay into leptons and photons. Pi0 is an up and anti-up or down and anti-down pair. Pi+ is up and anti-down pair. Pi - is anti-up and down pair.
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Neutrino (Electron Neutrino)
A lepton with very little mass and charge of 0. Lepton number of +1. Anti-neutrino has lepton number of -1.
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## Other cards in this set

### Card 2

#### Front

A quantity that is formed by the multiplication and/or division of one or more base quantities.

Derived Quantity

### Card 3

#### Front

A quantity with magnitude (size) only.

#### Back ### Card 4

#### Front

A quantity with both magnitude and direction.

#### Back ### Card 5

#### Front

The product of the force and the perpendicular distance from the pivot, to the line of action of the force.

#### Back 