Physics Keyword Glossary

Measurement Fundamentals

Keyword	Definition
Physical Quantity	A property of a material that can be measured.
Unit	A standard amount of a physical quantity.
International System of Units (SI Unit)	Promotes uniformity and consistency in measurements.
Base Quantities	Fundamental physical quantities (length, mass, time, etc.).
Derived Quantities	Quantities derived from base quantities (area, volume, speed, etc.).
Scientific Notation	A way to express very large or very small numbers using powers of 10.
Significant Figures	Digits that carry meaningful information in a measurement.
Density	Mass per unit volume of a substance.
Mass	The amount of matter in an object.
Weight	The force of gravity acting on a mass.

Forces and Motion

Keyword	Definition
Force (F)	A push or pull acting on an object.
Newton (N)	SI unit of force. 1 N = force needed to accelerate 1 kg at 1 m/s².
Friction	The force that opposes motion between two surfaces in contact.
Upthrust (Buoyancy)	The upward force exerted by a fluid on a submerged object.
Tension	The pulling force transmitted through a rope, string, or cable.
Normal Reaction	The perpendicular force exerted by a surface on an object in contact with it.
Resultant Force	The single force representing the combined effect of multiple forces.
Newton’s Second Law (F = ma)	Acceleration is proportional to force and inversely proportional to mass.
Newton’s First Law	Objects will remain at rest, or move with a constant velocity unless acted on by a resultant force.
Terminal Velocity	Constant velocity reached by a falling object when air resistance equals weight.
Centripetal Force	Resultant force that keeps an object in uniform circular motion.
Vector	Quantity with magnitude and direction.
Scalar	Quantity with magnitude only.
Magnitude	Size or amount of a physical quantity.
Resultant	Combined single vector having same effect.
Component	One of the perpendicular parts of a vector.
Perpendicular	At 90° angle.
Acceleration	The rate of change in speed.
Displacement	Shortest distance from initial point to final point (or distance in a specific direction).
Velocity	Speed in a specific direction.

Energy and Power

Keyword	Definition
Energy	The ability to do work.
Kinetic Energy	Energy of motion.
Gravitational Potential Energy	Energy stored in an object due to its position in a gravitational field.
Strain Energy	Energy stored in a stretched or compressed object.
Chemical Energy	Energy stored in chemical bonds.
Power	The rate of doing work or the rate of energy transfer.
Efficiency	Describes how much of the input energy or power is transferred usefully.
Turbine	A structure turned by a primary energy resource.
Generator	A structure that produces energy.
Renewable Resources	Energy sources that cannot be exhausted and generally not polluting.
Non-renewable Resources	Energy sources that can be exhausted and cannot be replaced in short time.

Light

Keyword	Definition
Light	Electromagnetic radiation that is visible to the human eye.
Ray	A straight line that represents the path of light.
Beam	A stream of light rays.
Straight-line propagation	Light travels in straight lines.
Normal	A line perpendicular to a surface at the point of incidence.
Boundary	The interface between two different media.
Reflection	The bouncing back of light from a surface.
Plane mirror	A flat mirror that produces a virtual image.
Incident ray	A ray of light that strikes a surface.
Reflected ray	A ray of light that bounces off a surface.
Angle of incidence	The angle between the incident ray and the normal.
Angle of reflection	The angle between the reflected ray and the normal.
Law of reflection	The angle of incidence equals the angle of reflection.
Refraction	The bending of light as it passes from one medium to another.
Refracted ray	A ray of light that has been bent as it passes through a boundary.
Transparent	Allowing light to pass through so that objects behind can be seen clearly.
Optical density	A measure of how much a medium slows down light.
Dispersion	Splitting of white light into different colours when it passes through a prism.
Spectrum	The range of colours into which white light is split by dispersion.
Prism	A transparent object with flat, polished surfaces that refracts light.
Critical Angle	The angle of incidence beyond which total internal reflection occurs.
Total Internal Reflection	The complete reflection of light within a medium when it strikes a boundary at an angle greater than the critical angle.

Pressure and Fluids

Keyword	Definition
Pressure	Force acting normally per unit area.
Pascal (Pa)	Unit of pressure.
Gauge Pressure	The pressure above atmospheric pressure.
Atmospheric Pressure	The pressure exerted by the Earth’s atmosphere.

Hooke’s Law

Keyword	Definition
Deform	Change in length (or shape).
Elastic deformation	The spring returns to its original length.
Plastic/inelastic deformation	The spring does not return to its original length.
Original length	Starting length ( $L_0$ ).
Stretched length	Length after force is applied ( $L$ ).
Extension	Difference between stretched length and original length.
Limit of proportionality	The point beyond which Hooke’s law is no longer obeyed.
Spring constant (k)	A measure of the stiffness of a spring.

Moments and Stability

Keyword	Definition
Moment	The turning effect of a force about a pivot.
Pivot	Point where turning occurs.
Perpendicular distance	Shortest distance from pivot to force line.
Clockwise moment	Moment that turns clockwise.
Anticlockwise moment	Moment that turns anticlockwise.
Equilibrium	Balanced – no turning.
Centre of Mass	The point where the whole weight of the body appears to act.
Stability	The ability of an object to resist toppling.
Stable equilibrium	An object returns to its original position after a small displacement.
Unstable equilibrium	An object moves away from its original position after a small displacement.
Neutral equilibrium	An object remains in its new position after a small displacement.

Impulse and Momentum

Keyword	Definition
Impulse	The product of force and time, equal to the change in momentum.
Momentum	The product of mass and velocity.
Conservation of Momentum	Total momentum before collision equals total momentum after collision.