Year 8 Physics: Forces, Motion, Light, Magnetism, and the Universe

Comprehensive vocabulary flashcards covering Year 8 Physics topics: Speed, Forces, Turning Moments, Pressure, Diffusion, Light, Reflection, Refraction, Magnetism, Electromagnets, Galaxies, and Exoplanetary Systems.

Speed

A measure of how fast an object is moving, calculated using the formula $\text{speed} = \frac{\text{distance}}{\text{time}}$, with the standard SI unit of metres per second ($\text{m/s}$).

Light Gate

An electronic instrument consisting of a light beam shining onto a light-sensitive switch that automatically starts and stops an electronic timer when an object breaks the beam to measure speed accurately.

Radar Speed-Trap Gun

A device that emits a beam of radio waves towards a moving vehicle and calculates its speed by measuring the time difference and Doppler shift of the reflected waves.

Distance-Time Graph

A graph that plots distance on the vertical axis against time on the horizontal axis, where a horizontal section represents a stationary object and the gradient represents speed.

Velocity

A description of both the speed and the direction of a moving object, such as an aeroplane flying at $900\,\text{km/h}$ due north.

Balanced Forces

Forces acting on an object that cancel each other out to produce a net resultant force of zero, causing the object to remain at rest or continue moving at a constant speed in a straight line.

Unbalanced Forces

Forces acting on an object that do not cancel out, producing a non-zero resultant force that causes the object to accelerate, decelerate, or change direction.

Normal Force

The perpendicular supporting force exerted upward by a surface against an object resting on it, balancing the object's downward weight.

Upthrust

The upward force exerted by a fluid (such as water) on an object submerged or floating in it, opposing the object's downward weight.

Plimsoll Line

A legal reference mark on a ship's hull introduced by Samuel Plimsoll in 1876 that indicates the maximum safe water level to prevent overloading in waters of varying density and temperature.

Bathyscaphe

A deep-ocean exploration craft that floods its air tanks with water to sink and slowly releases iron pellets to reduce weight and rise back to the surface.

Lever

A simple machine composed of two arms and a fulcrum that acts as a force multiplier, allowing a small effort applied over a long distance to overcome a large load over a short distance.

Fulcrum

The fixed support or pivot point about which a lever turns.

Moment of a Force

The turning effect produced by a force around a fulcrum, calculated by $\text{moment} = \text{force} \times \text{distance from the fulcrum}$ and measured in newton metres ($\text{Nm}$).

Principle of Moments

The law formulated by Archimedes stating that when an object is in equilibrium, the sum of clockwise moments about any point equals the sum of anti-clockwise moments about that point.

Pressure

The amount of force exerted per unit area, calculated using the equation $P = \frac{F}{A}$.

Pascal (Pa)

The standard SI unit for pressure, equivalent to one newton per square metre ($1\,\text{N/m}^2$).

Hydraulic System

A mechanism that utilizes an incompressible liquid to transmit pressure equally in all directions, functioning as a force multiplier in car brakes and hydraulic jacks.

Atmospheric Pressure

The downward pressure exerted in all directions by the layer of gases surrounding the Earth, measuring approximately $100\,000\,\text{N/m}^2$ at the surface.

Eustachian Tube

A tube connecting the throat to the middle ear that opens during swallowing to equalize the air pressure inside the middle ear with the pressure outside.

Hovercraft

A vehicle that uses fans to force air beneath a flexible skirt, creating a trapped cushion of high-pressure air that lifts it above land or water to reduce friction.

Diffusion

The process by which particles spread out and intermix from an area of high concentration to an area of low concentration due to their constant random motion.

Luminous Object

An object that produces and gives out its own light, such as the Sun or a lamp.

Incident Ray

A beam or ray of light that strikes a reflective or refractive surface.

Reflected Ray

A ray of light that bounces off a surface after striking it.

Normal (Optics)

An imaginary line drawn perpendicular ($90^\circ$) to a surface at the point where a light ray strikes it.

Law of Reflection

The scientific principle stating that the angle of incidence is equal to the angle of reflection ($i = r$), with both angles measured from the normal.

Specular Reflection

Orderly, mirror-like reflection occurring when parallel light rays strike a flat, smooth surface and reflect at identical angles, producing a clear image.

Diffuse Reflection

Scattered, irregular reflection occurring when light strikes a rough surface, dispersing the rays in different directions so no clear image is formed.

Refraction

The bending of a light ray as it passes at an angle from one transparent medium into another, caused by a change in the speed of light.

Dispersion

The splitting of white light into its constituent spectrum of colours when passing through a prism due to different colours refracting by slightly different amounts.

Spectrum

The continuous range of constituent colours produced when white light is dispersed, consisting of red, orange, yellow, green, blue, indigo, and violet.

Ole Rømer

The Danish astronomer (1644–1710) who demonstrated that light has a finite speed by calculating that eclipses of Jupiter's moons occurred earlier when Earth was closer in orbit.

Armand Fizeau

The French physicist (1819–1896) who measured the speed of light over a distance of $9\,\text{km}$ using a candle and timed apparatus, calculating a value of $314\,262\,944\,\text{m/s}$.

Primary Colours of Light

The three fundamental colours of light—red, green, and blue—which can be added together in equal intensity to produce white light.

Colour Subtraction

The process by which a transparent colour filter absorbs all colours of white light except its own colour, which it transmits.

Magnetic Field

The region around a magnet in which its magnetic force acts on magnetic materials or other magnets.

Magnetic Materials

Metals that are attracted to magnets, the primary examples being iron, steel, nickel, and cobalt.

Lines of Force

Lines that visually represent a magnetic field, pointing from North to South outside a magnet, where closer spacing denotes a stronger magnetic field.

Electromagnet

A temporary magnet constructed from a coil of wire wrapped around an iron core, which gains magnetism when an electric current flows and loses it when switched off.

William Gilbert

The English physician and scientist (1544–1603) who experimented with a spherical lodestone model of Earth, demonstrating that Earth acts like a giant magnet.

Hans Christian Ørsted

The Danish physicist (1777–1851) who discovered electromagnetism in 1820 after observing that an electric current passing along a wire deflected a nearby compass needle.

Galaxy

A massive gravitational system containing millions or billions of stars, stellar dust, gas, and planetary systems.

Milky Way

The spiral galaxy containing our Solar System, measuring approximately $100\,000\,\text{light-years}$ across and rotating once every $225$ to $250\,\text{million years}$.

Intergalactic Space

The vast, near-total vacuum situated between galaxies, characterized by an estimated density of only $1\,\text{atom}$ of hydrogen per cubic metre ($\text{m}^3$).

Spiral Galaxy

A pinwheel-shaped galaxy featuring a central bulge and winding outer arms, containing young and old stars, gas, and stellar dust clouds where stars form.

Elliptical Galaxy

A spherical or elongated football-shaped galaxy lacking spiral arms, composed predominantly of older stars with very little gas and dust.

Irregular Galaxy

A galaxy with no distinct symmetric shape, rich in dust and gas, often formed by gravitational interactions or collisions between galaxies.

Exoplanet

A planet that orbits a star located outside of our Solar System.

Transit Method (The Wink)

An indirect detection technique that identifies exoplanets by measuring the periodic dip in a star's brightness as a planet passes between the star and an observer.

Habitable Zone (Goldilocks Zone)

The orbital region around a star where the levels of heat and light are suitable for liquid water to exist on a planetary surface.

Asteroid

A small rocky remnant left over from the formation of the solar system that possesses its own gravity and orbits a star.