Reaction Time Test
How fast do you react? Catch a ruler as it falls on screen, then read your time where you caught it: the ruler’s other edge is a clock, drawn from the physics of a falling ruler.
Ruler
A longer ruler still catches a slower press. Changing it starts a new round.
- Press the ruler and it is held above your fingers.
- When it drops, press again as fast as you can to catch it.
- Read your catch at your fingers: centimetres on the left edge, your time on the right. 5 tries make a round.
With a keyboard, focus the ruler and use Space.
| Try | Caught at | Time Model |
|---|
4.9 cmNext 100 ms
14.7 cm
Press the ruler to hold it. When it drops, catch it. 5 tries make a round.
A falling ruler starts slow. Its first 100 ms of fall cover only 4.9 cm, and the next 100 ms cover 14.7 cm more. So the clock’s marks bunch up near your fingers: equal steps of ruler are not equal steps of time.
Your screen, and your mouse, key or touch, each add a delay of their own, so a time here reads a little slower than the same catch with a real ruler. In class, each student catches on their own phone, focused and then distracted, so that delay is in both catches and largely drops out of the difference, wherever both land on the ruler: a catch that falls through has no time to subtract.
Ruler-drop chart: read a real ruler’s catch
Have someone hold a ruler with its zero level with the top of your open finger and thumb, and let go without warning. Find where the top of your thumb caught it.
| Caught at (cm) | Reaction time (ms) Model |
|---|---|
| 1 | 45 |
| 2 | 64 |
| 3 | 78 |
| 4 | 90 |
| 5 | 101 |
| 6 | 111 |
| 7 | 119 |
| 8 | 128 |
| 9 | 135 |
| 10 | 143 |
| 11 | 150 |
| 12 | 156 |
| 13 | 163 |
| 14 | 169 |
| 15 | 175 |
| 16 | 181 |
| 17 | 186 |
| 18 | 192 |
| 19 | 197 |
| 20 | 202 |
| 21 | 207 |
| 22 | 212 |
| 23 | 217 |
| 24 | 221 |
| 25 | 226 |
| 26 | 230 |
| 27 | 235 |
| 28 | 239 |
| 29 | 243 |
| 30 | 247 |
| 35 | 267 |
| 40 | 286 |
| 45 | 303 |
| 50 | 319 |
| 55 | 335 |
| 60 | 350 |
| 65 | 364 |
| 70 | 378 |
| 75 | 391 |
| 80 | 404 |
| 85 | 416 |
| 90 | 428 |
| 95 | 440 |
| 100 | 452 |
Run the ruler drop with your class
Put it on a slide and your audience joins from their phones — no app and no accounts for them. Free to start.
Run the ruler drop with your class