Secondary 5 Physics

The energy transferred by a force along a displacement; W = Fs cosθ, measured in joules.

The ability to do work; energy only changes form and is never created or destroyed.

The energy an object possesses due to its motion, KE = ½mv².

The energy stored in an object because of its height, PE = mgh.

The energy transferred per second, P = W/t; measured in watts.

The unit of power; 1 watt equals 1 joule per second.

The unit of energy and work: 1 J is the work done by a 1 N force over 1 m along the displacement.

Energy is neither created nor destroyed, only converted from one form to another.

The projection of a force along a direction; only the component along the displacement does work.

The process of energy changing from one form to another, e.g. electrical energy into kinetic and internal energy.

The product of mass and velocity, p = mv; a vector in kg m s⁻¹.

Force times the period it acts, Ft, equal to the change in momentum mv − mu, in N s.

In a closed system with no external force, the total momentum is unchanged by a collision.

A system with no net external force; conservation of momentum holds only in this case.

An ideal collision in which kinetic energy as well as momentum is conserved.

A collision in which some kinetic energy becomes internal or sound energy, while momentum is still conserved.

How fast momentum changes with time; force equals the rate of change of momentum (another form of Newton's second law).

The backward motion of the rest of a system when mass is ejected, explained by conservation of momentum.

A row of suspended steel balls demonstrating the transfer and conservation of momentum and energy.

The constant force that would produce the same momentum change: the change in momentum divided by the time.

A disturbance that transfers energy without transferring matter; the medium only vibrates in place.

A wave vibrating perpendicular to its direction of travel, with crests and troughs; rope and water waves.

A wave vibrating parallel to its direction of travel, made of alternate compressions and rarefactions; sound.

The highest point of a transverse wave, where the displacement is maximum.

The lowest point of a transverse wave, where the displacement is maximum in the opposite sense.

The region of a longitudinal wave where particles are crowded together.

The region of a longitudinal wave where particles are spread apart.

The maximum displacement of a particle from equilibrium, reflecting the energy carried by the wave.

The distance between two neighbouring in-phase points, e.g. two adjacent crests; symbol λ.

The number of complete oscillations per second, in hertz (Hz); fixed by the source, T = 1/f.

The angle of reflection equals the angle of incidence, both measured from the normal, with the rays coplanar.

The line perpendicular to the surface at the point of incidence; all angles are measured from it.

The bending of light when it enters another medium and its speed changes.

n = c/v, measuring how much slower light is in a medium than in vacuum; water 1.33, glass about 1.5.

n₁ sin θ₁ = n₂ sin θ₂, relating the angles of incidence and refraction.

The angle between the incident ray and the normal.

The angle between the refracted ray and the normal; smaller than the incidence angle when entering a denser medium.

When light in a denser medium strikes the boundary beyond the critical angle, all of it reflects back.

The incidence angle at which the refracted ray travels along the surface; sin C = 1/n.

A thin strand that guides light along its core by total internal reflection; used in communications and endoscopes.

The substance sound travels through, such as air, water or steel; a vacuum carries no sound.

The speed at which sound travels; about 340 m s⁻¹ in air, rising slightly with temperature.

Sound reflected back from an obstacle; useful for measuring distances.

The range of frequencies the human ear can hear, about 20 Hz to 20 kHz.

Sound with frequency above 20 kHz, inaudible to humans; used in sonar and B-scans.

How strong a sound is, set by amplitude — larger amplitude, louder sound.

How high a note is, set by frequency — higher frequency, higher pitch.

The character of a sound, set by its waveform, letting us tell instruments apart.

The unit of sound intensity level; 0 dB is about the threshold of hearing, and prolonged exposure above 80 dB harms hearing.

A system that sends ultrasound pulses and times the echoes to locate objects underwater.

The branch of physics studying stationary charges, their interactions and applications.

A basic property of matter with only two kinds, positive and negative; like charges repel, unlike attract.

Charging by rubbing two objects together, transferring electrons so each gains equal and opposite charge.

Electrons moving from one object to another; the gainer becomes negative, the loser positive.

The redistribution of charge in an object when a charged body comes near, unlike charge gathering on the near side.

The region around a charged object in which another charge experiences an electric force.

Imaginary lines from positive to negative charge; denser lines mean a stronger field, and the direction gives the force on a positive charge.

The tendency of charge to leak away at sharp points, on which lightning conductors rely.

Connecting an object to the ground so excess charge flows away, preventing build-up and sparks.

A device that detects charge by the divergence of two metal leaves carrying like charges.