Cambridge IGCSE Physics 0625

1.1 Physical quantities and measurement techniques

Measure length, volume and time accurately, then learn how scalar and vector quantities differ.

Core Extended Practical skills

2026-2028 syllabus

What you need to learn

Core

Describe the use of rulers and measuring cylinders to find a length or a volume.
Describe how to measure a variety of time intervals using clocks and digital timers.
Determine an average value for a small distance and for a short time interval by measuring multiples, including the period of oscillation of a pendulum.

Extended: Core + Supplement

Understand that a scalar quantity has magnitude only and that a vector quantity has magnitude and direction.
Know that distance, speed, time, mass, energy and temperature are scalar quantities.
Know that force, weight, velocity, acceleration, momentum, electric field strength and gravitational field strength are vector quantities.
Determine, by calculation or graphically, the resultant of two vectors at right angles, limited to forces or velocities.

Key language

Definitions

Length

The distance from one point to another. Its SI unit is the metre (m).

Volume

The amount of space occupied by an object or substance. Its SI unit is the cubic metre (m³).

Time interval

The duration between two events. Its SI unit is the second (s).

Period

The time taken for one complete oscillation.

Parallax error

A reading error caused by viewing a scale from an angle instead of directly in line with the mark.

Meniscus

The curved surface of a liquid in a container.

Required for all candidates

Core

Measuring length

The SI unit of length is the metre (m). A ruler measures short lengths, usually to the nearest millimetre. Use a tape measure for distances of a few metres and a trundle wheel for longer distances.

Unit	In metres	Power of ten
1 kilometre (km)	1000 m	10³ m
1 centimetre (cm)	0.01 m	10^-2 m
1 millimetre (mm)	0.001 m	10^-3 m
1 micrometre (µm)	0.000001 m	10^-6 m
1 nanometre (nm)	0.000000001 m	10^-9 m

Cotton placed beside a ruler — **Fig. 1:** Measure both end positions and subtract the starting reading from the final reading.

Metric length units shown as powers of ten — **Fig. 2:** Common metric length units written using powers of ten.

Avoiding parallax error

Position your eye directly above or directly in line with the scale marking. Looking from an angle can make the reading larger or smaller than its true value.

Correct and incorrect eye positions when reading a scale — **Fig. 3:** The central eye position gives the correct reading; angled views cause parallax error.

Measuring volume

For a regular cuboid, measure its length, breadth and height. Measure liquid volume with a measuring cylinder. Keep the cylinder vertical and read the bottom of the meniscus at eye level.

Cube with one-centimetre sides — **Fig. 4:** A cube measuring 1 cm by 1 cm by 1 cm has a volume of 1 cm³.

Reading the bottom of a liquid meniscus at eye level — **Fig. 5:** Read the bottom of the meniscus at eye level.

Measuring time

The SI unit of time is the second (s). Choose a clock or digital timer with suitable precision. For a lap time, subtract the earlier cumulative reading from the later reading.

Stopwatch readings used to calculate a second lap time — **Fig. 6:** Second lap time = 2 min 03 s - 1 min 13 s = 50 s.

Practical skills

Experiment: period of a pendulum

Attach a small metal bob to a string and suspend it securely.

Pull the bob to one side through a small angle and release it without pushing.

Use a fixed reference point. Time 10 or 20 complete oscillations.

Repeat the timing, calculate a mean time, then divide by the number of oscillations to find T.

Pendulum oscillating from A through O to B — **Fig. 7:** One complete oscillation is A → O → B → O → A.

Core + Supplement

Extended

Scalar

Has magnitude (size) only.

Examples: distance, speed, time, mass, energy and temperature.

Vector

Has magnitude and direction.

Examples: force, weight, velocity, acceleration, momentum, electric field strength and gravitational field strength.

Resultant of two vectors at right angles

For two perpendicular forces or velocities, use Pythagoras to calculate the magnitude. A scale drawing can also be used: draw the vectors head-to-tail and measure the resultant from the start to the finish.

Calculating the resultant of perpendicular vectors — **Fig. 8:** Calculate a perpendicular resultant using Pythagoras.

Finding a resultant vector using a scale drawing — **Fig. 9:** Find a resultant graphically using an accurate scale drawing.

Equations and conversions

Equations

Length when the object does not start at zero

L = final reading - starting reading

Volume of a cuboid

V = l × b × h

Period from several oscillations

T = total time, t number of oscillations, N

Volume conversions

1 ml = 1 cm³
1000 cm³ = 1 litre
1 cm³ = 10^-6 m³

Extended

Perpendicular resultant

R = √(x² + y²)

Check your understanding

Questions

Core 1

A thread starts at 2.4 cm and ends at 15.6 cm on a ruler. Calculate its length.

15.6 cm - 2.4 cm = 13.2 cm

The thread is 13.2 cm long.

Core 2

A runner completes lap 1 at 1 min 13 s and lap 2 at a total time of 2 min 03 s. Find the time for lap 2.

Convert to seconds: 2 min 03 s = 123 s; 1 min 13 s = 73 s.

Lap 2 time = 123 s - 73 s = 50 s.

Core 3

A pendulum completes 20 oscillations in 36.0 s. Calculate its period.

T = 36.0 s 20 = 1.80 s

Core 4

State two steps needed to read liquid volume accurately in a measuring cylinder.

Keep the measuring cylinder vertical on a level surface.
Place the eye level with the liquid surface.
Read the bottom of the meniscus.

Any two correct points earn the marks.

Extended 1

A force of 6 N east and a force of 8 N north act on an object. Calculate the magnitude of the resultant.

R = √(6² + 8²) = √100

R = 10 N

Extended 2

Classify each quantity as scalar or vector: speed, velocity, mass and force.

Scalars: speed and mass.

Vectors: velocity and force.

Tap a card to reveal the answer

Flashcards

Next topic 1.2 Motion