# Definitions - G484 and G485

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Newton's First Law

A body at rest or in uniform motion will remain at rest or in uniform motion unless a resultant force acts

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Newton's Second Law

The rate of change of momentum is directly proportional and acts in the same direction as the resultant force acting upon it

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Newton's Third Law

If body A exerts a force on body B, then body B will exert an equal and opposite force on body A

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Linear Momentum

The mass of an object multiplied by its velocity

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Newton

The force that gives a mass of one kilogram an acceleration of one metre per second squared

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Principle of conservation of momentum

In any direction, with the absence of external forces, the total momentum of a system remains constant

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Impulse

The change in momentum of a body

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Perfectly elastic collision

One where no momentum or kinetic energy is lost

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Inelastic collision

Momentum is conserved but kinetic energy is not

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Radian

The angle subtended at the centre of a circle by an arc of length equal to the circle's radius

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Period

The time taken to complete one revolution

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Centripetal acceleration

The acceleration of a body moving in a circle with a constant speed

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Field

Region in which a force opperates

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Gravitational field strength

Force acting per unit mass at that point

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Gravitational force

Directly proportional to the product of their masses and inversely proportional to the square of the distance between them

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Kepler's Third Law

The period of a planet squared equals the mean radius of orbit cubed

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Displacement

The distance an object has moved from its mean (or rest) position

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Amplitude

The maximum dispacement

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Frequency

The number of oscillations per unit time at any point

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Period (SHM)

Time for one complete pattern of oscillations to take place at any point

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Damping

Deliberately reducing the amplitude of an oscillaiton

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Resonance

The build up of a large amplitude oscillation when the frequencies of vibrating objects match

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Phase

Whether a substance is a solid, liquid or gas

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Internal energy

The sum of the random distributions of kinetic and potential energies of all the molecules in the body

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Ideal Gas

Gas that has internal energy only in the form of random kinetic energy

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Thermal Equilibrium

Two objects at the same temperature

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Specific heat capacity

The quantity of thermal energy required to raise the temperature of a unit mass of a substance by a unit temperature rise

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Specific latent heat of fusion

Quantity of energy per unit mass required to change it at constant temperature from a solid into a liquid

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Specific latent heat of vaporisation

Quantity of energy per unit mass required to change it at constant temperature from a liquid into a vapour

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Boyle's Law

The volume of a fixed mass of gas is inversely proportional to the pressure exerted on it, provided the temperature is kept constant

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Boltzmann Constant

Gas constant for a single molecule

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Electric field strength

Force per unit positive charge

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Tesla

Magnetic flux density when a wire of length one metre and carrying a current of one ampere at a right angle to the field experiences a force of one newton

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Unified atomic mass unit

u - 1.66054X10-27

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Weber

Unit of magnetic flux - One weber (Wb) is the magnetic flux when a magnetic field of magnetic flux density one tesla passes through an area of one sqaure metre

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Magnetic Flux Linkage

For a coil - The magnetic flux through the coil multiplied by the number of turns on the coil

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Faraday's Law

The magnitude of induced e.m.f. is equal to the rate at which magnetic flux is cut

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Lenz's Law

The direction of any induced current is in a direction that opposes the flux change that causes it

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Capacitance

The charge stored per unit potential difference. Its unit is the Farad (F). One Farad is one coulomb per volt

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Time Constant

Containing a capacitor of capacitance C and a resistor of resistance R is given as CR

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Nucleon

A nuclear particle, either a proton or a neutron

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The nucleon number (A)

Number of nucleons in any nucleus

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The proton number (Z)

The number of protons in a nucleus

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Isotope

Two nuclides with the same number of protons but different number of neutrons

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Activity

The rate at which a source emits radioactive particles, measured in becquerels (Bq)

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Decay constant

Related the activity to the number of nuclei

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Half-life

The time taken for the activity of the activity of the source to decrease by one half. It is also the time taken for the number of radioactive nuclei to decrease by one half

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Binding energy

The energy required to separate an atom into its constituent parts

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Acoustic Impedance

Used to determine the fraction of the intensity refracted at a boundary between two materials of different acoustic impedances

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Hubble's Law

The speed of recession of a galaxy is directly proportional to its distance from the earth

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Cosmological Principle

On a large scale, the universe is isotropic (same in all directions) and homogeneous (uniform density) as long as a large enough volume is used

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## Other cards in this set

### Card 2

#### Front

The rate of change of momentum is directly proportional and acts in the same direction as the resultant force acting upon it

#### Back

Newton's Second Law

### Card 3

#### Front

If body A exerts a force on body B, then body B will exert an equal and opposite force on body A

#### Back

### Card 4

#### Front

The mass of an object multiplied by its velocity

#### Back

### Card 5

#### Front

The force that gives a mass of one kilogram an acceleration of one metre per second squared

#### Back

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