Definitions Flashcards
Vector
A physical quantity with magnitude and direction
Scalar
A physical quantity with magnitude only
Moment
Force times perpendicular distance from the line of action of the force to the point
Principle of moments
For an object in equilibrium, the sum of the clockwise moments is equal to the sum of the anticlockwise moments about any point
Couple
A pair of equal and opposite forces acting on a body, but not along the same line
Velocity
Change of displacement per unit time
Acceleration
Change of velocity per unit time
Newton’s 1st Law
An object will remain at rest or at a constant velocity unless acted on by an external resultant force
Newton’s 2nd Law
The force is proportional to the rate of change of momentum
Newton’s 3rd Law
For every action there is an equal and opposite reaction
Equilibrium
State of an object when at rest or moving at constant velocity
Density
Mass per unit volume of the substance
Stress
Force per unit area of cross section in a solid perpendicular to the cross section
Strain
Extension per unit length of a solid when deformed
Young’s Modulus
Tensile stress/strain
Limit of Proportionality
The limit beyond which, when a wire or a spring is stretched, its extension is no longer proportional to the force that stretches it
Plastic deformation
Deformation of a solid beyond its elastic limit
Elastic limit
Point beyond which a wire is permanently stretched
Hooke’s Law
The extension of a spring is directily proportional to the force applied to it, up to the limit of proportionality
Isotope
Atoms with the same number of protons but different numbers of neutrons
Conservation of energy
Energy cannot be created or destroyed, only converted from one form to another
Work done
Force times distance moved in the direction of the force
Ductile
Material that can be drwan into threads, it can be shaped or permanently deformed without fracture
Brittle
Material cannot be permanently stretched
Wave
Transfer energy from A to B via a medium of transfer, without transferring the medium
Standing wave
When two waves travel in opposing directions and they have the same wave speed, frequency and in general amplitude, they will superpose and form a standing wave
Monochromatic
Single wavelength
Coherent
No change in phase relationship
Collimated
Formed in a narrow beam
Diffraction
Spreading out or bending of waves as they pass through a gap or around an obstacle
Emf
Describes the amount of energy that is converted from one form to electrical and placed on a unit of charge at the source
Ohm’s Law
The current flowing through a metallic conductor is directly proportional to the potential difference across its ends, provided the temperature remains constant
Resistivity
The resistance of a piece of wire 1m in length and with a cross sectional area of 1m^2
Centre of mass
The point through which a single force on the body has no turning effect
Principle of conservation of linear momentum
The total linear momentum of a system of interacting bodies is constant, providing no external forces act
Work function
Minimum energy to liberate electron
Excitation
When an electrion takes in energy from a photon or collision and goes up an energy level
Ionisation
When an electron takes in enough energy to leave the atom
Motive power
Power outputted by a powered object (i.e. engine or muscle)
Progressive waves
Waves that move outwards from their source
Transverse waves
Each particle oscillates perpendicular to the direction of propagation to the wave
Longitudinal wves
Each particle oscillates parallel to the direction of propagation to the wave
Rarefied
More distance between particles than usual
Compression
Particles closer together
Mechanical waves
Oscillation of particles in a physical medium
Electromagnetic waves
Acceleration of charged particles, and can transmit energy through a vacuum
Refraction
Change in path of light ray caused by a change in speed
Total internal reflection
The angle of incidence is greater than the critical angle
Diffraction
The spreading of waves when passed through a gap or round an obstacle
Kirchhoff’s First Law
The sum of the currents leaving any junction is always equal to the sum of the currents that entered it
Kirchhoff’s Second Law
The sum of potential differences across components of a series circuit is equal to the emf
Internal Resistance
Resistance inside a source of electrical energy; the loss of pd per unit current in the source when current passes through it
Potential Divider
Two or more resistors in series connected to a source of pd
Superconductor
A material that has zero electrical resistance
Gravitational Field Strength
The force per unit mass acting on a small test mass placed in the field
Gravitational Potential
The work done to move a small object from infinity to that point in a gravitational field
Kepler’s First Law
All planets move about the Sun in elliptical orbits, having the Sun as one of the foci
Kepler’s Second Law
A radius vector joining any planet to the sun, sweeps out equal areas in equal lengths of time
Kepler’s Third Law
The square of the period of a planet’s orbit is proportional to the cube of the mean radius of its orbit
Coulomb’s Law
The magnitude of the force between two charges is proportional to the product of the charges and inversely proportional to the square of the distance between them
Electric Field
Region where a charged particle will experience a force
Gravitational Field
The region surrounding an object in which it exerts a gravitational force on any other object
Geostationary Satellite
A satellite that stays above the same point on the Earth’s equator as it’s period is 24 hours and has the same rotation direction
Electric Field Strength
Force per unit charge acting on a small positive test charge at a point in the field
Potential Gradient
Change of potential per metre at a point in a gravitational field
Electric Potential
Work done per unit positive charge moving a small positive charge from infinity to that point in the field
Field
A region around an object where a force is exerted
Capacitance
The charge stored per unit pd of a capacitor
Dielectric
Material that increases the capacity of a parallel-plate capacitor to store charge when placed between the plates of the capacitor
Activity
The number of unstable radioactive nuclei that decay per second
Metastable State
An excited state of the nuclei of an isotope that last long enough after α or β emission for the isotope to be separated from the parent isotope
Atomic Mass Unit
One twelfth of the mass of a carbon-12 atom
Mass Defect
Mass of separated nucleons minus mass of nucleus
Binding Energy
The work that must be done to separate a nucleus into its constituent nucleons
Critical Mass
The minimum mass required to sustain a chain reaction of fission in a nuclear reactor
Fuel Rods (Nuclear Reactor)
Contains enriched uranium. Increased % of U-235 compared to uranium ore it’s extracted from
Control Rods (Nuclear Reactor)
Made of cadmium or boron to absorb neutrons
Lifted in and out of the reactor to control the number of neutrons present and the rate of fission
Moderator (Nuclear Reactor)
Made of graphite or water
Slows down fission neutrons into one thermal energies, to increase the likelihood of absorption by U-235 nuclei
Coolant (Nuclear Reactor)
Water flows around the core, transferring heat away from the fuel, to be used to produce steam to drive a turbine
Angular Displacement
The angle moved through relative to a specific axis
Angular Velocity
The rate of change of angular displacement with respect to time
Centripetal Force
The force that makes an object move in a circle
Simple Harmonic Motion
Acceleration is proportional to the displacement of the object from equilibrium and is always directed towards the equilibrium position
Natural Frequency
The frequency of free oscillations of an oscillating system
Free Vibrations
Vibrations where there is no damping and no periodic force acting on the system, so the amplitude of the oscillations is constant
Forced Vibrations
Vibrations of a system subjected to an external periodic force
Resonance
The driving force matches the natural frequency of the system, leading to an increased amplitude of oscillation
Damping
The removal of energy from an oscillating system
Magnetic Flux Density
The magnetic force per unit length per unit current on a current carrying conductor at right angles to the field lines
Electromagnetic Induction
The generation of an emf when the magnetic flux linkage through a coil changes or a conductor cuts across magnetic field lines
Lenz’s Law
The direction of the induced emf is always such as to oppose the change that causes the emf
Hall Probe
A device used to measure magnetic flux density
Magnetic Flux
The product of magnetic flux density and the area perpendicular to the field
Magnetic Flux Linkage
A measure of the magnetic flux of a coil of wire
Faraday’s Law of Electromagnetic Induction
The induced emf in a circuit is equal to the rate of change of magnetic flux linkage through the circuit
Eddy Current
Induced currents in the metal parts of ac machines
Internal Energy
Sum of Ep and Ek of molecules within the body
Boyle’s Law
When a fixed mass of gas is reduced in volume by a compressing piston, the pressure inside the piston increases
Charles’ Law
For the fixed mass of an ideal gas at constant pressure, its volume is directly proportional to its absolute temperature
Ideal Gas
A gas under conditions such that it obeys Boyle’s Law
