IGCSE 0625 / Section 1.2 / Core

How fast, and which way.

Speed tells you how quickly distance is covered. Velocity adds the critical missing word: the direction. They share one simple equation, but the difference between a scalar and a vector runs right through the rest of mechanics.

The key idea

Speed is the distance travelled per unit time, a scalar. Velocity is speed in a stated direction, a vector. Both come from v = s / t, measured in metres per second (m/s).

Section 01

Distance, time, and the ratio between them.

Set a constant speed and release the trolley. Watch how distance continuously grows while the object is moving, then see how displacement handles the return trip differently from distance.

Stage 1 · Learn

Check what the trolley showed you

Four quick checks on speed, velocity, and the distance-displacement split. Each correct answer earns XP and lights this skill on your star map.

Quick check+10 XP

As the trolley keeps moving forward, the distance it has travelled...

Quick check+10 XP

When the trolley returns exactly to its starting point, its displacement is...

Quick check+10 XP

Velocity is a vector while speed is a scalar because velocity also states...

Quick check+10 XP

The equation linking speed v, distance s and time t is...

Section 02

Speed, velocity, and average speed.

Examiner trap

Two cars travelling at the same speed in opposite directions have different velocities, because velocity includes direction. When a question gives a direction, or asks about a change in direction, it is testing velocity, and the sign or compass bearing is a required part of your answer.

Worked example

A cyclist travels 1.5 km in 5.0 minutes at a steady rate. Calculate the average speed in m/s.

Step 1 · Convert to SI units firstdistance = 1.5 km = 1500 m; time = 5.0 min = 300 s.
Step 2 · Apply the equationv = s / t = 1500 m / 300 s
Step 3 · Answerv = 5.0 m/s. Converting to metres and seconds before substituting avoids the most common error here.
Stage 2 · Exam

Exam-style questions

Unlocks once the four checks above are done. Worth more XP, written in the style of Paper 1.

Finish the four checks above to unlock the exam questions
Exam style+20 XP

A cyclist travels 1500 m in 300 s at a steady rate. The average speed is...

Exam style+20 XP

Two cars travel at 30 m/s in opposite directions. They have...

Exam style+20 XP

A car drives 4 km north, then 4 km back south, taking 0.5 h in total. Its average velocity is...

Skill unlocked

Speed and velocity, mastered.

This skill is now lit gold on your star map. Keep the chain going.

-Rank -Level -Score -Topics
Go deeper · practice
Six original Cambridge-style questions
Defining speed and velocity, the scalar versus vector distinction, average speed, and rearranging distance, speed and time. Attempt each, then reveal the worked solution.
Stage 3 · master the unit
Motion, forces and energy challenge
Mixed questions across the whole unit, each one worth XP. Start this only when you feel confident across every topic in the unit, not just speed and velocity.
Start the unit challenge →