All Definitions Needed For A Level


This post contains all the important formulas that you need for A Level Physics. (Equivalent to AP Physics) If you do not recognise any of the terms listed here, you should go review the respective topic.

Please drop me a comment if I missed out any particular important definitions.

Measurement:
Random errors are errors of measurements in which the measured quantities differ from the mean value with different magnitudes and directions.

Systematic errors are errors of measurements in which the measured quantities are displaced from the true value by fixed magnitude and in the same direction.

Accuracy is a measure of how close the results of an experiment agree with the true value.

Precision is a measure of how close the results of an experiment agree with each other.

Thermal Physics:
The internal energy is a function of state and the total microscopic kinetic and potential energies of the particles  composing the system.

The specific latent heat of fusion, Lf , is defined as the amount of heat required per unit mass to change a substance from the solid phase to the liquid phase without any change in temperature

The specific latent heat of vaporization, Lv, is defined as the amount of heat required per unit mass to change a substance from the liquid phase to the vapor phase without any change in temperature.

First law of thermodynamics state that internal energy is a function of state and the increase in internal energy is equal to the sum of the heat supplied to system and work done on system.



Kinematics:
Speed is the rate of change of distance traveled with respect to time.

Velocity is the rate of change of its displacement with respect to time.

Acceleration of an object is the rate of change of its velocity with respect to time.


Forces And Dynamics:
Normal contact force is a force perpendicular to the surface experienced by a body when it is in physical contact with something else.

Hooke’s Law states that within the limit of proportionality, the extension produced in a material is directly proportional to the load applied.

The principle of moments states that, when an object is in equilibrium, the sum of anticlockwise moments about any point equals the sum of clockwise moments about the same point.

The moment of a force is the product of the force and the perpendicular distance between the axis of rotation and the line of action of the force.

A couple is a pair of forces, equal in magnitude but opposite in direction, whose lines of motion do not coincide.

Centre of gravity is the point on an object through which the entire weight of the object may be considered to act.

Stability of an object refers to its ability to return to its original position after it has been displaced from that position.

Pressure is force acting per unit area.

Upthrust/buoyancy force is an upward force on a body produced by the surrounding fluid (i.e., a liquid or a gas) in which it is fully or partially immersed, due to the pressure difference of the fluid between the top and bottom of the object.

Archimedes’ Principle states that the upthrust experienced by an object partially or entirely immersed in a fluid is equal to the weight of the fluid displaced by the object.

Newton’s first law of motion states that a body will continue in its state of rest or uniform motion in a straight line unless an external resultant force acts on it.

Newton’s second law states that the rate of change of momentum of a body is proportional to the resultant force acting on it and the change takes place in the direction of the force.

Newton’s third law states that: If body A exerts a force on body B, then body B exerts a force of equal magnitude but in the opposite direction on body A.

The principle of conservation of momentum states that the total momentum of a system of objects remains constant provided no resultant external force acts on the system.

Work, Energy And Power:
Work is the mechanical transfer of energy to a system or from a system by an external force on it.

Heat is the non-mechanical transfer of energy from the environment to the system or from the system to the environment because of a temperature difference between the two.

The principle of conservation of energy states that energy cannot be created nor destroyed in any process.

Gravitational Potential Energy is defined as the amount of work done in order to raise the body to the height h from a reference level.

Power is defined as the rate of work done or energy converted with respect to time.


Circular Motion:
Angular displacement, θ is the angle subtended at centre of a circle by an arc of equal length to the radius.

Angular velocity, ω is the rate of change of angular displacement with respect to time.

The period T of an object in circular motion is the time taken for the object to make one complete revolution.

The frequency f of an object in circular motion is the number of complete revolutions made by the object per unit time.


Waves:
Displacement is the distance moved by the particle from its equilibrium position.

The amplitude of a wave is the maximum displacement of the particle from its equilibrium position.

The wavelength is the distance between 2 successive points on a wave which are in phase with one another.

The period is the time taken for a particle on the wave to complete one oscillation.

The frequency of a wave is the number of complete oscillations that pass through a given point in 1 second. (Units: Hertz(Hz) or s-1)

A compression is a region where particles are close to one another. (High pressure)

A rarefaction is a region where the particles are further apart. (Low pressure)

Phase Difference (φ) between two particles or two waves tells us how much a particle (or wave) is in front or behind another particle (or wave).

Intensity of a wave is the rate of transfer of energy per unit area perpendicular to the direction of travel of the wave.


Oscillations:
Periodic motion is the regular, repetitive motion of a body which continually retraces its path at regular intervals.

Period T of a periodic motion is the time to make one complete cycle.

Frequency f of a periodic motion is the number of cycles per unit time.

Angular frequency of a periodic motion is the rate of change of angular displacement with respect to time.

Displacement of an object is the distance of the oscillating particle from its equilibrium position at any instant.

Amplitude of a periodic motion is the magnitude of the maximum displacement of the oscillating particle from the equilibrium position.

Simple Harmonic Motion (SHM) is defined as the oscillatory motion of a particle whose acceleration a is always directed towards a fixed point and is directly proportional to its displacement x from that fixed point but in the opposite direction to the displacement.

Damping is the process whereby energy is taken from the oscillating system.

Natural frequency of the system is the frequency at which it will vibrate freely.

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17 thoughts on “All Definitions Needed For A Level”

  1. The definitions for waves aren’t correct since a lot of them assume that the waves require a medium. The definitions as a whole are correct but a lot wouldn’t get you the marks in an exam.

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