- Acceleration
- How quickly the velocity of something changes.
- Air resistance
- The force from air pushing against something moving through it.
- Amplitude
- The height of a wave from its middle line.
- Atom
- The tiny building block of everything around you.
- Balanced forces
- Forces that cancel out, so the net force is zero.
- Big Bang
- The event about 13.8 billion years ago when our universe began expanding.
- Boiling
- A liquid turning quickly into a gas.
- Buoyancy
- The ability to float, thanks to upthrust.
- Calorie
- An older unit of energy. One food calorie is about 4.2 kilojoules.
- Circuit
- A complete loop that electricity can flow around.
- Collision
- When two objects crash or bump together.
- Compound
- A substance made of two or more kinds of atom joined together.
- Conduction
- Heat passing through a material, from particle to particle.
- Conservation of energy
- Energy can move and change form, but never appears or disappears.
- Convection
- Heat carried by moving liquid or gas.
- Current
- The flow of electric charge. It is measured in amps.
- Deceleration
- Slowing down. It is acceleration in the opposite direction to the motion.
- Density
- How much mass is packed into a certain space.
- Displacement
- How far and in which direction something has ended up from where it started.
- Distance
- How far apart two places are, or how far something has travelled.
- Echo
- A sound that bounces back to you.
- Elastic collision
- A bouncy collision, where no movement energy is lost.
- Electric charge
- A property of tiny particles that makes them attract or repel.
- Electromagnet
- A magnet made by electricity flowing through a coil.
- Electromagnetic waves
- Waves of electric and magnetic energy, including light and radio.
- Electron
- A tiny negative particle that moves around the nucleus.
- Element
- A substance made of just one kind of atom.
- Energy
- What makes things able to happen. It is measured in joules.
- Evaporation
- A liquid slowly turning into a gas at its surface.
- Force
- A push or a pull on something.
- Force pair
- Two equal and opposite forces that two objects put on each other.
- Frequency
- How many waves pass each second. It is measured in hertz.
- Friction
- A force between surfaces that rub together. It resists sliding.
- Galaxy
- A huge collection of stars, gas and dust held by gravity.
- Gas
- Matter that spreads out to fill any space.
- Gradient
- How steep a line is on a graph.
- Graph
- A picture that shows how one number changes with another.
- Gravitational potential energy
- Energy stored in something because of its height.
- Gravity
- The pull between all things that have mass.
- Grip
- How well two surfaces hold on to each other.
- Heat
- Energy moving from something hotter to something cooler.
- Impulse
- Force multiplied by time. It equals the change in momentum.
- Inertia
- The way things keep doing what they are doing unless a force changes it.
- Instantaneous speed
- How fast something is going at one exact moment.
- Insulator
- A material that heat or electricity cannot pass through easily.
- Joule (J)
- The unit of energy. It takes about 1 joule to lift an apple 1 metre.
- Kilojoule (kJ)
- One thousand joules. Food labels use it.
- Kinetic energy
- The energy something has because it is moving.
- Latent heat
- Energy used to change a state, such as melting, with no change in temperature.
- Lens
- A curved piece of clear material that bends light.
- Lever
- A bar that turns on a pivot, used to move loads with less force.
- Lift
- The upward force on a wing as it moves through the air.
- Light
- Energy that travels as waves you can see.
- Light year
- The distance light travels in one year.
- Liquid
- Matter that flows and takes the shape of its container.
- Loudness
- How strong a sound seems.
- Magnet
- An object that attracts iron and has north and south poles.
- Magnetic field
- The area around a magnet where its force can be felt.
- Mass
- How much stuff is in an object. It is measured in kilograms.
- Melting
- A solid turning into a liquid.
- Molecule
- Two or more atoms joined together.
- Moment
- The turning effect of a force.
- Momentum
- Mass multiplied by velocity. It tells you how hard something is to stop.
- Motor
- A machine that turns electricity into movement.
- Nerve
- A body cell or bundle that carries electrical signals.
- Net force
- The total force left over after adding up all the pushes and pulls.
- Neutron
- A particle with no charge in the nucleus of an atom.
- Newton (N)
- The unit of force. One newton is about the weight of a small apple.
- Normal line
- An imaginary line at right angles to a surface.
- Nuclear fusion
- Small atoms joining to make a bigger one, and releasing energy.
- Nucleus
- The tiny, dense centre of an atom.
- Opaque
- Not letting light through.
- Orbit
- The curved path of one thing around another, held by gravity.
- Origin
- The starting point that positions are measured from.
- Particle
- A very tiny piece of matter, such as an atom or a molecule.
- Pascal (Pa)
- The unit of pressure. One pascal is one newton on each square metre.
- Photon
- A tiny packet of light energy.
- Pitch
- How high or low a sound is.
- Pivot
- The point that something turns around.
- Planet
- A large round world that orbits a star.
- Position
- Where something is, measured from a starting point.
- Potential energy
- Energy stored, ready to be used, like a ball held up high.
- Power
- How quickly energy is transferred. It is measured in watts.
- Pressure
- How much force presses on each bit of area.
- Proton
- A positive particle in the nucleus of an atom.
- Pulley
- A wheel and rope that make lifting easier.
- Quanta
- The tiny packets that energy comes in. One packet is called a quantum.
- Quantum
- A smallest possible amount of something, such as energy.
- Radiation
- Energy moving as waves, even through empty space.
- Reflection
- Light or sound bouncing off a surface.
- Refraction
- Light bending as it goes from one material into another.
- Relativity
- Einstein's ideas about space, time, mass and energy.
- Resistance
- How much something slows down current. It is measured in ohms.
- Retina
- The layer at the back of your eye that senses light.
- Satellite
- Something that orbits a planet, like the Moon or a space station.
- Shadow
- A dark area where an object blocks the light.
- Simple machine
- A tool that changes the size or direction of a force.
- Solid
- Matter with a fixed shape, like a rock.
- Sound
- Vibrations that travel through air or other materials.
- Spectrum
- All the colours of light, spread out in order.
- Speed
- How far something goes in each second.
- Static electricity
- Electric charge that has built up in one place.
- Temperature
- How hot or cold something is.
- Terminal velocity
- The steady top speed of a falling object, when air resistance balances weight.
- Thrust
- The push that drives something forward, like a rocket or a swimmer.
- Tide
- The daily rise and fall of the sea, caused mainly by the Moon's gravity.
- Ultrasound
- Sound too high for people to hear.
- Unbalanced forces
- Forces that do not cancel out, so something changes its motion.
- Upthrust
- The upward push of a liquid or gas on something in it.
- Vacuum
- A space with nothing in it, not even air.
- Vector
- A quantity with both a size and a direction, such as force.
- Velocity
- Speed in a particular direction.
- Vibration
- A very fast shaking movement to and fro.
- Voltage
- The push that makes current flow. It is measured in volts.
- Watt (W)
- The unit of power. One watt is one joule every second.
- Wave
- A pattern that carries energy from place to place.
- Wavelength
- The distance from one wave crest to the next.
- Weight
- The force of gravity pulling on you. It is measured in newtons.
- Work
- Energy transferred when a force moves something.