This guide puts fourteen confusing Physics terms side by side, each with a plain meaning, an original example and the lesson or module that teaches it. Use it when a question feels like it could mean two things.
The English, BM and Chinese concept bridge shows the same terms across languages, which helps if you learn in Malay or Chinese at school but answer in English.
Motion and forces
Distance and displacement
Distance is the total length of the path travelled, and it has no direction. Displacement is the straight-line change in position with a direction. A student walks 60 m to a shop and 60 m back: distance 120 m, displacement 0 m.
Learn it: distinguish displacement from total distance.
Speed and velocity
Speed says how fast. Velocity says how fast and in which direction. A car at 20 m/s north and another at 20 m/s south have the same speed and different velocities.
Learn it: motion and graphs.
Scalar and vector
A scalar has size only, such as mass or time. A vector has size and direction, such as force or displacement.
Learn it: scalar and vector descriptions.
Mass and weight
Mass is the amount of matter, in kilograms, and it does not change with place. Weight is the gravitational force on that mass, in newtons. A 3.0 kg bag has weight 30 N where g is 10 N/kg.
Learn it: mass and gravitational force.
Force and pressure
Force is a push or pull in newtons. Pressure is force spread over an area, so the same force on a smaller area gives a larger pressure.
Learn it: pressure in solids and fluids.
Balanced forces and no forces
A book on a table has two forces acting, weight and the table’s support, and they balance. “Balanced” does not mean “nothing is acting”.
Learn it: balanced forces versus no forces.
Energy and heat
Energy and power
Energy is what is stored or transferred, in joules. Power is how fast it is transferred, in watts, which means joules per second. A 60 W lamp transfers 60 J every second.
Learn it: power and energy resources.
Heat and temperature
Temperature tells you how hot something is. Thermal energy depends on temperature, mass and the material. A bath of warm water holds more thermal energy than a hot cup of tea.
Learn it: temperature versus thermal energy.
Waves and light
Reflection and refraction
Reflection is a wave bouncing off a surface. Refraction is a wave changing direction because its speed changes in a new material.
Learn it: reflection and refraction with wavefronts.
Transverse and longitudinal
In a transverse wave the vibration is at right angles to the direction of travel, like a ripple. In a longitudinal wave it is along the direction, like sound.
Learn it: transverse and longitudinal motion.
Frequency and amplitude
Frequency is how many waves pass each second, in hertz. Amplitude is the maximum displacement from the rest position. Louder sound means greater amplitude, and higher pitch means higher frequency.
Learn it: pitch and loudness separately.
Electricity and nuclear physics
Current and potential difference
Current is the flow of charge through a component, in amperes. Potential difference is the energy transferred per unit charge between two points, in volts. Current goes through a lamp, and potential difference is across it.
Learn it: charge and current.
Resistance and current
Resistance tells you how much a component opposes current, in ohms, using R = V ÷ I. A 12 V supply across a 4 Ω resistor gives 3 A, so a larger resistance means a smaller current, not a larger one.
Learn it: using a resistance relationship with units.
Background radiation and half-life
Background radiation is the radiation present around us from natural and other sources. Half-life is the time for the activity of a sample to halve. Subtract the background before you work with half-life data.
Learn it: half-life and background.
Check yourself
1. A runner completes one 400 m lap and ends where she began. State her distance and displacement.
Show answer
Distance 400 m, displacement 0 m.
2. A 5.0 kg object is on Earth where g is 10 N/kg. State its mass and weight.
Show answer
Mass 5.0 kg, weight 5.0 × 10 = 50 N.
3. Is the current or the potential difference measured across a lamp?
Show answer
Potential difference is across the lamp, and current is through it. A voltmeter goes in parallel with the lamp.
Where to go next
Pick the pair that cost you marks most recently and open its lesson. The Physics learning guide shows where each one sits in the course, and the original practice hub gives you fresh questions to test the choice.
A teacher can also check which pair you mix up in a live question during online one-to-one Physics tuition.