Physics Definitions

Velocity

rate of change of displacement

Acceleration -

rate of change of velocity

Newton's First Law -

An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

Newton's Second Law -

Force equals mass times acceleration

Newton's Third Law -

Every action has an equal and opposite reaction

Elastic collision -

momentum and kinetic energy are conserved

Inellastic collision -

a collision in which only momentum is conserved

Centre of gravity -

The point where the entire weight of an object appears to act.

Torque of a couple -

The force multiplied by the perpendicular distance between the forces

principle of moments -

The sum of the clockwise moments is equal to the sum of the anticlockwise moments of a body in equilibrium.

capacitance -

the amount of charge stored per unit of P.D

electrical potential -

work done moving unit positive charge from infinity to the point

electrical field strength -

Force per unit positive charge

Doppler effect -

An observed change in the frequency of a wave when the source or observer is moving

spontaneous decay -

Decay is not affected by environmental factors

Random Decay -

cannot tell which nucleus will decay next; cannot state at what time a nucleus will decay;

Diffraction of a wave -

When a wave incident to a slit bends

Electric field -

a region of space where a charge will experience a force

Isotope -

Atoms of the same element that have different numbers of neutrons

Luminosity -

The total power emitted by a star.

luminous flux -

the rate at which light is emitted from a source

Hubble's Law -

The observation that the farther away a galaxy is, the faster it is moving away.

Momentum -

The product of an object's mass and velocity

principle of moments -

The sum of the clockwise moments is equal to the sum of the anticlockwise moments.

angular displacement -

the angle turned through in circular motion

angular velocity -

rate of change of angular displacement

centripetal acceleration -

the acceleration of an object moving in a circle, directed toward the centre

centripetal force -

the resultant force towards the centre of a circle acting on an object moving in a circular path

Accuracy -

A description of how close a measurement is to the true value of the quantity measured.

Precision -

a measure of how close a series of measurements are to one another

conservation of momentum -

Momentum of a system remains constant when there are no net external forces acting on it.

terminal velocity -

the constant velocity of a falling object when the force of air resistance is equal in magnitude and opposite in direction to the force of gravity

centre of gravity -

The point where the entire weight of an object appears to act.

centre of mass -

The point through which a single force on the body has no turning effect

couple -

Two equal and opposite parallel forces that act on an object through different lines of action. It has the effect of causing a rotation without translation.

conservation of energy -

Energy cannot be created or destroyed only transferred from one form to another

efficiency -

The percentage of the input work that is converted to output work

gravitational potential energy -

Energy stored by objects due to their position above Earth's surface.

kinetic energy -

the energy an object has due to its motion

Power -

the rate at which work is done

work done -

force x distance

Compressive deformation -

A change in the shape of an object due to compressive forces

elastic deformation -

region where the material will return to its original shape when the stress is removed

plastic deformation -

permanent deformation caused by strain when stress exceeds a certain value

elastic limit -

Maximum stress that a material will withstand without permanent deformation.

elastic potential energy -

the potential energy of an object that is stretched or compressed

Hooke's Law -

Extension is directly proportional to force until the spring reaches it's elastic limit

Limit of proportionality -

The limit beyond which, when a wire or spring is stretched, its extension is no longer proportional to the force that stretches it.

spring constant -

a constant that represents the relationship between the force exerted by a spring and its change in length. Higher spring constantx

strain -

ratio of an objects extension to its original length

stress -

force acting per unit area

tensile strength -

the resistance of a material to breaking under tension

Tensile strain -

The extension per unit length

tensile stress -

The force per unit cross-sectional area, measured in Pa

Young's Modulus -

A measure of the stiffness of an elastic material and defined by stress/strain.

Amplitude -

the height of a wave from the origin to the crest

electromagnetic spectrum -

Gamma, X-ray, UV, Visible, Infrared, Micro, Radio

Intensity -

The amount of energy per second carried through a unit area by a wave.

Phase Difference (SHM) - .

Difference in position in cycle of two points expressed as an angle

longitudinal wave -

A wave in which the vibration of the medium is parallel to the direction the wave travels

Transverse wave -

A wave that moves the medium in a direction perpendicular to the direction in which the wave travels

Polarisation -

The restriction of a wave so that it can only oscillate in a single plane. This can only occur for transverse waves.

Progressive wave -

A wave that transfers energy without transferring matter

Antinode -

A point of maximum amplitude on a standing wave

coherence -

Waves with the same frequency and constant phase difference.

constructive interference -

The interference that occurs when two waves combine to make a wave with a larger amplitude

destructive interference -

The interference that occurs when two waves combine to make a wave with a smaller amplitude

Diffraction -

Occurs when an object causes a wave to change direction and bend around it

diffraction grating -

a device made of thousands of closely spaced slits through which light is passed in order to produce a spectrum

interference -

Superposition of two progressive waves from coherent sources to produce a resultant wave with a displacement equal to the sum of the individual displacements from the two waves

Nodes -

The point of minimum displacement in a stationary wave

superposition principle -

when two or more waves overlap, the resulting wave is the sum of the individual waves

Two source interference -

When the waves from two sources interfere to produce a pattern

charge -

the property of a particle that causes it to experience a force in an electromagnetic field

current -

The rate of flow of charge

Light dependent resistor -

Resistor which is designed to have a resistance that changes with light intensity

Ohmic conductor -

A conductor for which the current flow is directly proportional to the potential difference across it, when under constant physical conditions.

potential difference -

the difference in electrical charge between two points in a circuit expressed in volts

Power (circuit) -

rate of energy transfer

resistance -

a measure of how difficult it is for current to flow through a material

Resistivity -

a measure of the resisting power of a specified material to the flow of an electric current.

thermistor - A resistor that changes its resistance with a change of temperature.

A resistor that changes its resistance with a change of temperature.

Volt -

unit of potential difference

conservation of charge -

the principle that net electric charge is neither created nor destroyed but is transferable from one material to another

electromotive force (emf) -

The energy supplied by a source per unit charge passing through the source, measured in volts.

Internal resistance -

resistance inside the source of electrical energy - loss of PD per unit current in the source when current passes through it

Kirchoff's first law (current) -

The sum of the currents entering any junction is always equal to the sum of the currents leaving the junction (a form of conservation of charge).

Kirchoff's Second Law -

The sum of the e.m.f.s is equal to the sum of the p.d.s in a closed loop (a form of conservation of energy).

potential divider -

two or more resistors in series connected to a source of pd

Alpha Particle -

2 protons 2 newtrons highly ionising lowly penetrating

atomic mass unit (amu) -

one twelfth the mass of a carbon-12 atom

Beta particle -

A fast-moving electron that is given off as nuclear radiation. medium ionising, medium penetrating

Beta minus decay -

The process of a neutron inside a nucleus turning into a proton, and emitting a beta-minus particle (an electron) and a antineutrino.

Beta plus decay -

The process of a proton inside a nucleus turning into a neutron, and emitting a beta-plus particle (a positron) and a neutrino.

Electron -

a negatively charged subatomic particle

Hadrons -

Particles that are affected by strong nuclear force, and contain quarks

Leptons -

A group of elementary subatomic particles, consisting of electrons, muons and neutrinos.

Meson -

A hadron consisting of a quark and an antiquark

Positron -

a particle with the mass of an electron but a positive charge

Quark -

particles of matter that make up protons and neutrons