AS Physics (9702) Topically Sorted Definitions

Comprehensive list of physics definitions for AS Level (9702), covering kinematics, dynamics, waves, and electricity.

Scalar quantity

A scalar quantity has magnitude (only).

Vector quantity

A vector quantity has magnitude and direction.

Precision

Precision is determined by the range in the measurements/values/readings/data/results or the size of the smallest division (on the measuring instrument).

Accuracy

How close measured value is to the true quantity value.

Distance

Length/measure of space traversed by a body in motion.

Displacement

Distance in a specified direction (from a point).

Speed

Rate of change of distance or change in distance divided by time taken $v = \frac{\Delta d}{\Delta t}$.

Velocity

Rate of change of displacement or change in displacement divided by time taken $v = \frac{\Delta s}{\Delta t}$.

Acceleration

Rate of change of velocity or change in velocity divided by time (taken) $a = \frac{\Delta v}{\Delta t}$.

Mass

Mass is the property (of a body/object) resisting changes in motion or mass is the quantity of matter (in a body).

Linear momentum

Product of mass and velocity $p = mv$.

Newton’s first law of motion

A body/mass/object continues (at rest or) at constant/uniform velocity unless acted on by a resultant force.

Force / Newton’s second law of motion

(Resultant) force is (proportional OR equal to) rate of change of momentum $F_{net} = \frac{dp}{dt}$.

Newton’s third law of motion

Force on body A (by body B) is equal in magnitude and opposite in direction to the force on body B (by body A) $\pm F_A = \mp F_B$.

Weight

The weight of a body is the force acting on the body due to the gravitational field / the force due to gravity or gravitational force $W = mg$.

Principle of conservation of momentum

Sum/total momentum (of a system of bodies) is constant or sum/total momentum before is equal to sum/total momentum after for an isolated system or no (resultant) external force $\sum m_i u_i = \sum m_i v_i$.

Centre of gravity of a body

The point where (all) the weight (of the body) is taken to act.

Moment of a force

Force multiplied by perpendicular distance (of line of action of force) to/from a point.

Torque of a couple

Torque is the product of one of the forces and the perpendicular distance between the forces $T = rF \sin(\theta)$.

Principle of moments

For a body in (rotational) equilibrium sum/total of clockwise moments about a point is equal to sum/total of anticlockwise moments about the (same) point.

Density

Mass per unit volume or mass divided by volume $\rho = \frac{m}{V}$.

Pressure

Force per unit area (normal to the force) $P = \frac{F}{A}$.

Work done

Work done is the force multiplied by the distance moved / displacement in the direction of the force or work done is when a force moves in the direction of the force $W = Fd \cos(\theta)$.

Efficiency

Ratio of useful energy output from the system to the total energy input $\eta = \frac{E_{output}}{E_{input}} \times 100$.

Kinetic energy

The energy/ability to do work a object/body/mass has due to its speed/velocity/motion/movement $E_k = \frac{1}{2} mv^2$.

Gravitational potential energy

The energy/ability to do work of a mass that it has or is stored due to its position/height in a gravitational field $E_p = mgh$.

Elastic potential energy

Elastic PE energy stored (in an object) due to (a force) changing its shape / deformation / being compressed / stretched / strained.

Power

Work done per unit time $P = \frac{W}{t}$.

Hooke’s law

Extension is proportional to force (for small extensions) $F = kx$.

Stress

Force per (cross-sectional) area $\sigma = \frac{F}{A}$.

Strain

Extension divided by original length or change in length divided by original length $\epsilon = \frac{e}{l_0}$.

Young modulus

Ratio of stress to strain $E = \frac{\sigma}{\epsilon}$.

Elastic limit

Point beyond which (the spring) does not return to its original length when the load is removed.

Elastic deformation

When upon removal of load/deforming force, the material returns back to its original shape or (temporary) deformation that is reversed/recovered upon removal of external force causing it.

Plastic deformation

When upon removal of load/deforming force, the material does not return back to its original shape or (permanent) deformation that keeps the shape of the material altered despite of removal of external force causing it.

Wave motion

Means of moving energy from place to place.

Displacement (Progressive Wave)

Distance (in a specified direction of particle/point on wave) from the equilibrium position.

Amplitude (Progressive Wave)

The maximum distance (of particle/point on wave) from the equilibrium position or the maximum displacement (of particle/point on wave).

Phase difference

The amount by which one wave lags or leads another expressed using phase angle, or the difference in the phases of two oscillating particles, expressed in degrees or radians.

Period (Progressive Wave)

Time for one oscillation/one vibration/one cycle or shortest time between two wavefronts/points in phase $T = \frac{1}{f}$.

Frequency (Sound Wave)

Frequency is the number of vibrations/oscillations per unit time or the number of wavefronts passing a point per unit time $f = \frac{1}{T}$.

Wavelength (Progressive Wave)

Distance moved by wavefront/energy during one cycle/oscillation/period or minimum distance between two points having the same displacement and moving in the same direction $\lambda = \frac{v}{f}$.

Speed (Wave)

Speed at which energy is transferred / speed of wavefront $v = \frac{\lambda}{T}$.

Transverse wave

Vibrations (in plane) normal to direction of energy propagation (by reference to direction of propagation of energy).

Longitudinal wave

Vibration(s)/oscillation(s) (of particles) parallel to direction of propagation of energy (with reference to direction of propagation of energy).

Doppler effect

Change/difference in the observed/apparent frequency when the source is moving (relative to the observer) $f_o = \frac{f_s v}{v \pm v_s}$.

Principle of superposition

When waves meet / overlap (at a point), the (resultant) displacement is the sum of the individual displacements.

Node (Stationary Wave)

Position (along wave) where amplitude / displacement of vibration is zero.

Antinode (Stationary Wave)

Position (along wave) where amplitude of vibration is a maximum.

Diffraction

Diffraction is the spreading of a wave as it passes through a slit or past an edge.

Diffracted waves

Waves spread at (each) slit/gap.

Interference

When two (or more) waves superpose/meet/overlap, the resultant displacement is the sum of the displacement of each wave.

Coherence

Constant phase difference between (each of) the waves.

Electric field

A region/space/area where a (stationary) charge experiences an (electric) force.

Electric field strength

Force per unit charge acting on a stationary point charge $E = \frac{F}{Q}$.

Field line (line of force)

Path/direction in which a (free) positive charge will move in an electric field.

Electric current

Flow of charge carriers $I = \frac{Q}{t}$.

Quantised

Charge exists only in discrete amounts (referring to charge on carriers).

Coulomb

Ampere second $C = A\,s$.

Potential difference (p.d.)

Work done per unit charge (or energy transformed from electrical to chemical per unit charge driven between two points on a circuit).

Volt

Joule per coulomb $V = J\,C^{-1}$.

Resistance

Potential difference per current $R = \frac{V}{I}$.

Ohm

Volt per ampere $\Omega = V\,A^{-1}$.

Ohm’s law

The current in a metallic conductor is directly proportional to the potential difference across its ends, provided its temperature remains constant.

Electromotive force (e.m.f.)

Energy transformed from chemical to electrical per unit charge (driven around a complete circuit).

Kirchhoff’s first law

Sum of current(s) into junction is equal to sum of current(s) out of junction $\sum I_{in} = \sum I_{out}$.

Kirchhoff’s second law

Sum of electromotive force(s) is equal to sum of potential difference(s) around a loop/around a closed circuit $\sum E = \sum V$.

Nucleon number

The number of neutrons and protons in the nucleus of an atom.

Proton number

The number of protons in the nucleus of an atom.