Definitions Flashcards
Vector
A vector quantity has a magnitude AND a direction. Examples include Force, Velocity, Acceleration.
Scalar
A scalar quantity has a magnitude only. Examples include Mass, Charge, Energy.
Displacement
The distance travelled in a particular direction.
Velocity
The distance travelled in a certain direction per unit time.
Speed
The distance travelled per unit time.
Instantaneous speed
The speed at any particular instant in time.
Average speed
The overall distance travelled divided by the time taken.
Acceleration
The change in velocity per unit time.
1 Newton
The force on a 1kg mass which is being accelerated by 1ms-2.
Drag Force/Friction Force
The force on an object which opposes the motion of the object, or the tendency of the object to move.
Weight
The gravitational force acting on an object.
Terminal velocity
The constant velocity of an object, achieved when the frictional forces balance the driving force.
Moment of force
A Turning or Rotational Force, given by the product of the Force and the perpendicular distance from the pivot point or axis of rotation.
A Couple
A pair of equal but opposite forces with lines of action separated by a distance. The couple tends to produce rotation only.
Torque of a couple
The produce of one of the forces in a couple, and the perpendicular distance between them.
Equilibrium
The state of an object such that the total force and total moment acting on it are zero.
Stress
The applied force per unit area.
Strain
The extension produced per unit length.
Young’s Modulus
The stress per unit strain when a material is behaving elastically.
Breaking stress
The maximum possible stress applied to a material before fracture.
Elastic deformation
Deformation which is fully recovered when the force on an object is removed.
Plastic deformation
Deformation which is NOT fully recovered when the force on an object is removed.
Center of mass
The point where the entire weight of an object appears to act.
Thinking distance
The distance a vehicle will travel during the time the driver takes to see the problem and apply the brakes.
Thinking time
The time taken for the driver to see a problem and apply the brakes.
Braking distance
The distance taken for the vehicle to come to rest when the brakes are applied.
Braking time
The time taken for the vehicle to come to rest when the brakes are applied.
Stopping distance
The total distance taken for a vehicle to come to rest from the point where the incident is first seen. Given by the thinking distance plus the braking distance.
Work done
The amount of energy converted from one form to another.
The product of the applied force on an object and the distance over which the force is applied.
1 Joule
The kinetic energy a 2kg mass has when it moves with a speed of 1ms-1.
The gravitational potential energy a 0.1kg mass has when held 1m above the Earth’s surface.
Conservation of energy
For an isolated system, the total energy is a constant value.
Energy cannot be created or destroyed, only converted from one form to another.
Power
The rate of work done
1 Watt
The power of an engine which is converting 1J of energy in 1 second.
Potential difference
The change of electrical potential energy into other forms, when 1 C of charge moves between two points.
Current
The positive charge flowing per unit time.
Electrical resistance
The opposition to the flow of current. Given by the ratio of the voltage per unit amp.
The voltage per unit current.
Resistivity
The resistance between the ends of a 1m length of material which has a cross-sectional area of 1m2.
Mean drift speed of electrons
The average distance travelled along a wire per unit time.
EMF
The electrical potential energy per unit charge converted into other forms from a battery or power supply.
Potential difference
The electrical potential energy change between two points in a circuit per unit charge.
1 Coulomb
The amount of charge flowing in 1 second when a current of 1A flows.
1 Volt
The potential difference across a 1 resistor, which causes a current of 1A to flow.
1 Ohm
The resistance of a resistor with a potential difference of 1V across it and a current of 1A flowing through it.
Ohm’s law
For a metallic conductor at constant temperature, the current through it is directly proportional to the potential difference across its ends.
1 Amp
The current flowing through a resistor of 1Ω with a potential difference of 1V across it.
Kirchhoff’s First Law
Based on conservation of charge, at any point in a circuit, the total current into the point is equal to the total current out of the point.
Kirchhoff’s Second Law
Based on conservation of energy, for any closed loop in a circuit, the sum of the EMFs is equal to the sum of the potential differences.
Terminal potential difference
The potential difference between the actual contacts of a power supply. Given by the EMF of the supply minus the internal voltage drop.
Mean drift velocity
The average distance travelled by an electron through a circuit, per unit time.
1Kw-hr
An amount of electrical energy equal to 3.6 million Joules of energy.
Displacement
The distance moved, in a particular direction, from the rest point by an oscillating particle.
Amplitude
The maximum distance moved from the rest point.
Wavelength
The length for one complete cycle.
Period
The time taken for one complete cycle.
Frequency
The number of cycles per unit time.
Intensity
The power per unit cross-sectional area.
Longitudinal wave
A wave where the oscillations of the particles or field are parallel to the direction of motion of the wave.
Transverse wave
A wave where the oscillations of the particles or field are perpendicular to the direction of motion of the wave.
Progressive wave
A wave which transfers energy or information through the medium as a result of the oscillations of particles or a field.
Standing wave
A wave which does not transfer energy or information through the medium as a result of the oscillations of particles or a field.
Phase difference
The amount by which two waves are out of step with each other.
Path difference
The difference in distance travelled for two waves coming from different sources but reaching the same point.
Wave speed
The distance travelled by a wave per unit time. Given by the product of the wavelength and frequency of a wave.
Coherence
Two waves are coherent if the phase between them is constant in time.
Interference
When two or more coherent waves of the same type overlap and their displacements sum together, changing the overall intensity.
Superposition
When two waves of the same type overlap the resulting displacement if the sum of the individual displacements of the waves.
Constructive interference
Waves have a phase difference of 0° so that the interference produces a maximum possible displacement.
Destructive interference
Waves have a phase difference of 180° so that the interference produces a minimum possible displacement.
Node
The point on a standing wave, created by destructive interference such that there is no movement.
Antinode
The point on a standing wave, created by constructive interference such that there is maximum movement.
Fundamental mode of vibration
The standing wave of largest wavelength that can exist.
Fundamental wavelength
The highest wavelength of standing wave that can exist in a system.
Fundamental frequency
The lowest frequency of standing wave that can exist in a system.
Harmonic
A standing wave which has a frequency which is a multiple of the fundamental frequency.
The electron volt
The energy gained or lost by an electron when it moves through a voltage of 1 volt.
Work Function
The smallest amount of energy needed to eject an electron from an atom.
Threshold frequency
The frequency below which, the photons do not have enough energy to eject an electron.
Newton’s first law of motion
An object will move at constant velocity unless acted upon by an unbalanced force.
Newton’s second law of motion
The total unbalanced force on an object is directly proportional to the rate of change of momentum and the unbalanced force is in the same direction as the rate of change of momentum.
Newton’s third law of motion
For every force there is an equal but opposite force.
Linear momentum
The product of the mass and velocity of an object.
Net force on a body
The rate of change of momentum.
Impulse
The change of momentum of an object.
The product of the force on an object and the time over which the force acts.
Conservation of linear momentum
For an isolated system, the total linear momentum in any direction is a constant.
Perfectly elastic collision
A collision where kinetic energy is conserved.
Completely inelastic collision
A collision where kinetic energy is conserved.
Inelastic collision
A collision where kinetic energy is NOT conserved.
Radian
A unit of angle where one full circle (360°) is equivalent to 2pi radians.
Gravitational field strength
The gravitational force per unit mass.
The gravitational flux per unit perpendicular area.
Gravitational potential
The energy needed to bring a unit point mass from infinity to a given location.
Newton’s law of gravitation
The force (F) between two point masses (M1 and M2), a distance d apart is given by: F= (GM1M2)/d^2
Electric field strength
The electric force per unit positive charge.
The electric flux per unit perpendicular area.
Electric potential
The energy needed to bring a unit point charge from infinity to a given location.
Geostationary orbit
The orbit of a satellite such that it is directly above a fixed point on the Earth.
Internal energy
The sum of the total kinetic energy and potential energy of the atoms/molecules in a system.
Pressure
The force per unit Area.
Absolute zero
The temperature at which the internal energy of a system is a minimum.
Boyle’s law
For a system at constant temperature, the product of pressure and volume is a constant.
PV = constant.
1 mole
The amount of a substance such that there are 6.02 x 1023 basic particle present.
Avogadro’s `constant
6.02 x 1023 – the number of particles in a system when there is 1 mole present.
Specific heat capacity
The amount of heat energy needed to raise 1kg of a substance by 1K.
Latent heat of fusion
The amount of heat energy needed to change 1kg of a solid into a liquid.
Latent heat of vaporisation
The amount of heat energy needed to change 1kg of a liquid into a gas.
Magnetic flux
A measure of the magnetic field strength, draw as a set of lines whose density is proportional to the field strength. Measured in Webers (Wb).
Magnetic Flux Density / Magnetic Field Strength
A strength of a magnetic field, given by the magnetic Flux lines per unit Area perpendicular to the flux lines. 2
Measured in Tesla (T) or Wb/m^2
1 Tesla
The magnetic field strength required to produce a 1N force on a wire of 1m length, with a 1A current flowing
1 Weber
The number of flux lines through a 1m2 area in a field of strength 1T
Magnetic flux linkage
The product of the magnetic field strength and the number of turns in a coil
Lenz’s Law
The induced EMF is in such a direction as to oppose the change producing it
Faraday’s Law
The induced EMF has a magnitude given by the rate of change of flux linkage
Capacitance
The stored charge in a capacitor per unit voltage across the plates
1 Farad
The capacitance of a capacitor which stored a charge of 1C when a voltage of 1V is across the plates
Capacitive Time Constant
The produce of the capacitance of a capacitor and the resistance through which it is charging or discharging.
The time taken for a capacitor to reduce its charge to approximately 37% of its maximum value.
The time taken for a capacitor to reach approximately 63% of its maximum charge.
Displacement
The distance moved, in a particular direction, from the rest point by an oscillating particle.
Amplitude
The maximum distance moved from the rest point.
Period
The time taken for one complete cycle
Frequency
The number of cycles per unit time
Intensity
The power per unit cross-sectional area
Angular Speed/Angular Frequency
The angle turned through per unit time
Phase difference
The amount by which two waves are out of step with each other
Path difference
The difference in distance travelled for two waves coming from different sources but reaching the same point
Simple Harmonic Motion
The motion of an object such that its acceleration is directly proportional to the distance from a fixed point and the direction is always directed to the fixed point
Atomic number
The number of protons contained within the nucleus of an atom
Radioactive activity
The number of decays per unit time
Decay constant
The probability of an isotope decaying per unit time
Conservation of Lepton number
The total Lepton Number before a nuclear change will equal the total Lepton number after
Conservation of Baryon number
The total Baryon Number before a nuclear change will equal the total Baryon Number after
Binding Energy
The energy required to disassemble the protons and neutrons in a nucleus into their separate parts
Binding energy per nucleon
The energy per particle, required to disassemble the protons and neutrons in a nucleus into their separate parts.
Half life
The time taken for the activity of a substance to reduced to 50% of its value.
Electromagnetic intensity
The electromagnetic power per unit area.
1 AU
The average distance between the Earth and the Sun.
1 Light year
The distance light travels in a vacuum in 1 year
The parsec
The distance away an object would be to have a subtended angle of 1 second of an arc
Olbers’ Paradox
For an infinite and uniform universe, the sky at night should be light not dark.
Hubble’s Law
The speed of a receding galaxy is directly proportional to its distance from us
Cosmological principle
When viewed on a sufficiently large scale, the properties of the universe are the same for all observers
Critical density
The density of the universe that will give rise to a flat spacetime
