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Science · Force and motion

Speed: distance and time

Who is faster: someone who runs 100 metres in 15 seconds, or someone who cycles 1 kilometre in 3 minutes? Find out that speed is distance travelled divided by time taken, and learn the units m/s and km/h and how to convert between them.

  • 18 min
  • 2 simulations
  • Mini quiz

Updated:

Preview

The question

Elif cycles to school and Can walks. Elif's route is longer, but she gets to school before Can. How can we say for certain who is "faster"? Is it enough to look only at the distance travelled, or only at the time taken?

Try it yourself

No account needed: change the values and check your answer. Some simulations ask for a prediction before they start; it doesn't matter whether it's right or wrong.

Number line

Find the bike's speed

Drag the marker or move it with the arrow keys. When you are sure of the value, submit your answer.

Prediction

Predict first

Elif covers 600 m in 2 minutes and Can runs 100 m in 15 seconds. Which of them do you think is faster?

It doesn’t matter whether you’re right; the simulation opens once you choose.

Pendulum

Build a seconds pendulum

Change the string length and the starting angle with the sliders. Watch the pendulum swing; the stopwatch on screen shows how long a number of full swings take. When you find the length whose period is closest to 2 seconds, submit your answer.

Prediction

Predict first

If you make the pendulum's string longer, how does the time for one full swing there and back change?

It doesn’t matter whether you’re right; the simulation opens once you choose.

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Frequently asked

4 questions

Are speed and velocity the same thing?

In everyday language they are used to mean the same thing, but in science speed only tells you how fast something is going, while velocity also gives the direction of motion. "60 km/h" is a speed; "60 km/h towards the north" is a velocity.

Is average speed the average of the two speeds?

Not always. Average speed is the total distance divided by the total time. If you travel 60 km in 1 hour and return the same 60 km in 2 hours, you cover 120 km in 3 hours; your average speed is 40 km/h, not 45 km/h.

Why do we multiply by 3.6 to turn m/s into km/h?

There are 3600 seconds in an hour. Someone moving at 1 m/s covers 3600 m, or 3.6 km, in one hour. So to go from m/s to km/h you multiply by 3.6, and to go from km/h to m/s you divide by 3.6.

Is the number on a car's speedometer the average speed?

No. The speedometer shows the speed at that moment, called the instantaneous speed. Because you speed up, slow down and stop at red lights along the way, the average speed of the journey is usually lower than the highest value you see on the speedometer.