Mega Collection of Physics Definitions

Accurate

average value moves towards the true value

Precise

data are closer together

Random error

readings have positive and negative values around the average value

Systematic error

the readings are not centred around the true value

Zero error

a non-zero reading when a zero reading is expected

Acceleration

Rate of change in velocity per unit time

Average speed

speed over a period of time

Conservation of energy

Energy can not be created or destroyed, it just changes form

Conservation of momentum

if the net external force acting on a system is zero, the momentum remains constant

Coefficient of friction

ratio between (maximum) friction and normal reaction

Elastic collision

A collision in which kinetic energy is not lost

Force

A rate of change of momentum

Impulse

Change in momentum

Impulse of a force

Force x Time for which force acts

Instantaneous speed

the speed at a particular instant in time

Linear Momentum

Product of mass and velocity

Newton’s first law

A body continues at rest or constant velocity unless acted on by a resultant force

Newton’s second law

the rate of change of momentum of a body is directly proportional to the force acting on the body

Newton’s third law of motion

When two bodies A and B interact the force that A exerts on B is equal and opposite to the force that B exerts on A

Power

the rate at which work is being performed

Translational equilibrium

sum of the (net) forces acting on the object is zero

Work

Distance moved in the direction of the force

Boyle’s law

for and ideal gas at constant temperature, pressure is inversely proportional to volume

Heating of copper

The non-mechanical transfer of energy from source to copper

Heat capacity of body

energy required to increase the temperature of a substance by 1°C or 1K

Ideal Gas

A gas that obeys the universal gas laws at all pressures, volumes, and surfaces

Ideal gas assumptions

• large number of molecules

• molecules in random motion

• no intermolecular forces

• elastic collisions

• time of collisions much less than time between collisions

• volume of molecules much less than volume of containing vessel

Internal energy

sum of total kinetic energy and intermolecular potential energy in particles

Mole

the molecular weight of the element in grams

Specific Heat Capacity

the energy required to change the temperature by one unit degree per unit mass

Specific latent heat of fusion

the thermal energy absorbed when a unit mass of liquid freezes at a constant temperature

Specific latent heat of vaporization

quantity of thermal energy required to convert a unit mass of liquid to gas with no change in temperature

Temperature of a substance

temperature is proportional to a measure of the average kinetic energy of the particles of the substance

Thermal capacity

energy required to raise temperature of object by 1K

Thermal energy

the non-mechanical transfer of energy between two different bodies as a result of a temperature difference between them

Thermal equilibrium

rate of energy absorption is equal to the rate of energy emission

Adiabatic process

A change in the pressure, volume and temperature of the system in which no thermal energy transferred between the system and the surroundings

First law of thermodynamics

the energy transferred between a system and its surroundings is equal to the work done on the system plus the change in internal energy of the system

Increase in entropy

increase of degree of disorder in the system

Isobaric process

a process that takes place at constant pressure

Isochoric process

a process that takes place at constant volume

Isothermal process

a process in which temperature remains constant

Isothermal-Isobaric process

a process that takes place at constant temperature and pressure

Second law of thermodynamics

second law states total entropy of universe increases for any change

Amplitude

the maximum displacement of the system from equilibrium

Antinode

maximum amplitude

Coherent

zero phase difference between light waves

Coherence sources

sources whose phase difference is constant

Constructive interference

when two waves meet, resultant displacement is found by summing the individual displacements to give maximum displacement

Continuous travelling wave

An energy transfer without mass motion of the medium

Critical angle

when a ray is incident on the boundary at an angle greater than the critical angle, the ray is totally internally reflected;

Diffraction

spreading out of a wave when it meeds a slit

Displacement (waves)

distance in a particular direction of a particle from its mean position

Frequency of the source

number of oscillations per unit time

Interference

when waves overlap, resultant displacement is the sum of the individual displacements

Intensity of a sound wave

power per unit area

Longitudinal wave

a wave where the oscillations of particles are parallel to the direction of energy propogation

Monochromatic

light with the same frequency

Node

point in a standing wave with zero amplitude

Principle of superposition

when 2 waves meet, the net displacement of the particles is the sum of their individual displacements

Polarized light

light in which the electric field vibrates only in one plane

Ray

direction which energy of wave travels in relation to wavefront

Resonance

maximum amplitude of oscillation that occurs when a periodic force is applied to it and the frequency of the force is equal to the natural frequency of vibration of the system

Refractive index

the ratio of the speed of light in a vacuum to the speed of light in a substance

Simple harmonic motion

acceleration is proportional to the displacement from an equilibrium point in the opposite direction to the distance.

Transverse wave

the direction of energy propagation is at right angles to the vibration of the particles in the medium

Travelling (progressive) wave

a wave that transfers energy between points in a medium

Total internal reflection

for a ray attempting to move from a high to a low refractive index medium, the phenomena in which the angle of incidence is greater than the critical angle, which is the angle of incidence for which the angle of refraction is 90°, leading to a reflected but not to a refracted ray;

Unpolarized light

all possible polarization directions are equally represented

Wavefront

line that joins points with same phase, perpendicular to the wavefront

Wavelength

distance moved by wave during one oscillation of the source

Wave speed (speed of wave)

distance travelled per unit time by a wavefront

Wave speed (energy)

rate at which energy is propagated along the wave

Conduction electrons

free electrons that are not bound to any one particular atom of the metal

Coulomb’s law

the force between two point charges that is inversely proportional to the square of their separation and directly proportional to the product of their magnitudes

Electric current

The amount of charge that flows through a cross-sectional area of a conductor per unit time

Electric field strength

electric force per unit charge acting on a test positive charge

Electric field

area of space where a charge experiences a force

Electric potential difference

work done per unit charge to move positive test charge between points in an electric field

Electric potential difference

work done per unit charge that is transferred

Electric resistance

potential difference across the wire divided by the current through the wire

Electromotive force

the work done per unit charge in moving a quantity of charge completely around a circuit

Ideal voltmeter

infinite resistance

Internal resistance of a cell

resistance of the components within the cell itself, leading to energy dissipated in driving current through the cell

Kirchhoff’s first law

Sum of current = 0 at a junction

Kirchhoff’s second law

sum of e.m.f. = sum of p.d. around a loop

Ohm’s law

Potential difference is proportional to current, provided that the temperature is constant

Gravitational field

region of space where a mass experiences force

geostationary satellite

satellite that orbits with the same period of rotation as Earth, meaning it remains in the same position above Earth

gravitational field strength

the gravitational force per unit mass that is acting on a point mass

gravitational field strength at a point

force per unit mass acting on a point mass

Kepler’s third law

The square of the orbital period of rotation of a planet around the sun is proportional to the cube of the average radius of orbit

Newton’s universal law of gravitation

the attractive force between two point masses is directly proportional to the product of the masses and inversely proportional to the square of the distance between their centres of mass

Absorption spectrum

missing frequencies in otherwise continuous spectrum

Activity

the number of radioactive disintegrations per unit time

Alpha -particle

helium nucleus

Antiparticle

a particle with the same rest mass but opposite charge

Artificial (induced) transmutation

a particle is fired at a nucleus, and a different nucleus forms

Binding energy of a nucleus

energy released when a nucleus is formed from its constituent nucleons

Elementary particle

particle with no internal structure