Measuring Motion β€” Savanna Speed Lab

Film an animal crossing the savanna, pause the tape, measure how far it travelled and how long it took, then work out its speed.

1 Β· Choose your subject

Playback is slowed β€” the clock shows real time

2 Β· Roll the tape

PAUSED
00:00.00
Field of view: 24 m Β· the acacias are planted exactly 5 m apart
0.00 s

3 Β· Read the tape

  1. Pause where the animal is fully in view, then press Mark start β€” flag A lands on its nose.
  2. Scrub forward and press Mark end to drop flag B.
  3. Read the four numbers below off the ruler and the clock. The sim will not do the arithmetic for you.
  4. You can also drag either flag to line it up by eye.
Starting position  x₁
β€” m
Ending position  xβ‚‚
β€” m
Start time  t₁
β€” s
End time  tβ‚‚
β€” s

Tip: the acacias are exactly 5 m apart β€” use them to sanity-check your positions.

4 Β· Do the maths yourself

1
How far did it travel?

distance = ending position βˆ’ starting position  β†’  xβ‚‚ βˆ’ x₁

d = m
2
How long did it take?

time = end time βˆ’ start time  β†’  tβ‚‚ βˆ’ t₁

t = s
3
How fast was it going?

speed = distance Γ· time  β†’  d Γ· t

v = m/s
Your speed
β€” m/s
Same speed in other units
β€” km/h

5 Β· Which animal is fastest?

Speed you measured, in metres per second

No trials saved yet β€” work out a speed above, then press Save this trial.
Animals are drawn to true relative size within the 24 m field of view, and the acacias are planted exactly 5 m apart.

How to use this simulation

  1. Pick an animal. Click a chip in step 1 to choose which animal you'll film, and choose whether it's Walking or Running. Use the playback-speed buttons (1Γ—, Β½Γ—, ΒΌΓ—, β…’Γ—) to slow the action down β€” the on-screen clock always shows real time, no matter the playback speed.
  2. Roll the tape. Press β–Ά Play in step 2 to start the animal moving across the scene. Use ⟲ Rewind, the step buttons (β—€β—€ β—€ β–Ά β–Άβ–Ά), or drag the scrub bar to move the tape backward or forward one frame at a time β€” you can also use the arrow keys on your keyboard (hold Shift for bigger jumps).
  3. Mark a start point. Pause when the animal is clearly in view, then press 🚩 Mark start (A) in step 3. This drops a red flag on its nose and records the position and time.
  4. Mark an end point. Scrub the tape forward, then press 🏁 Mark end (B) to drop the blue flag further along. You can fine-tune either flag by dragging it left or right, or nudging it with the arrow keys.
  5. Read the numbers. The starting position (x₁), ending position (xβ‚‚), start time (t₁), and end time (tβ‚‚) appear as soon as both flags are placed. Use the ruler above the scene and the acacia trees β€” planted exactly 5 m apart β€” to double-check your readings.
  6. Work out the distance. In step 4, subtract the starting position from the ending position and type your answer into the d = box, then press Check. Wrong answers get a hint; keep trying until it's correct.
  7. Work out the time. Once distance is correct, subtract the start time from the end time and enter it in the t = box, then press Check.
  8. Work out the speed. Once time is correct, divide distance by time and enter the result in the v = box, then press Check to reveal the speed in metres per second and its equivalent in km/h and mph.
  9. Save your trial. Press οΌ‹ Save this trial to add your result to the bar chart and table in step 5, so you can compare speeds across different animals and gaits. Press Start over to clear the calculator, or Clear to remove the flags and try the same animal again.

Tips: Toggle πŸŒ™ Dark / β˜€οΈ Light in the top-right corner for a night version of the scene. Press the spacebar to play or pause from anywhere on the page. Try comparing the same animal's walking speed to its running speed, or race several animals and see whose bar comes out longest on the chart.