# PH1 Definitions

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- Created by: SianyMorris
- Created on: 01-04-17 15:45

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

Loading characteristics are significantly different to unloading characteristics. The region between the curves is the energy input per load-unload cycle.

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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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Hadron

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.

#### Back

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

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