Rocket crouches at the start line with a tennis ball. "I bet the ball beats my jog," he says.
Raven holds the timer. "Predict first, then measure. Same distance for every trial."
Nova hovers over the finish tape. "Remember to start the timer when the ball leaves the line, not before."
Rocket rolls. Raven counts. "Four point two seconds," she reads. Rocket jogs the same stretch. "Three point one."
"What do you notice?" Raven asks, writing both numbers down.
Rocket blinks. "The jog was faster. I was wrong. That is why we measure."
Nova brightens. "A wrong prediction with good data is a great result."
Today you measure three motions over the same distance: a walk, a jog and a rolling ball.
You will time each one, then divide the distance by the time to get a speed.
Predict the order before you start. Then let the numbers decide.
| Motion | Distance (metres) | Time, trial 1 (seconds) | Time, trial 2 (seconds) | Speed (metres per second) |
|---|---|---|---|---|
| Walk | ||||
| Jog | ||||
| Rolling ball |
Your two times for the same motion will not match exactly. Starting and stopping a timer by hand takes a moment.
That is normal. Scientists repeat trials for exactly this reason.
OpenStax gives a handy check. A marble that travels 5.2 metres in 1.8 seconds has an average speed of about 2.9 metres per second.
The text calls that about the speed of a brisk walk. Compare it with your own walking speed.
If your speed came out above 10 metres per second, check the division. That would be more than three brisk walks at once.
| What the lab shows | True or false? |
|---|---|
| Over the same distance, a shorter time means a higher speed. | ? |
| Two timings of the same motion should always match exactly. | ? |
| Repeating a trial helps you see how much the timing varies. | ? |
| A brisk walk is roughly 3 metres per second. | ? |
Careful measuring. Tomorrow you will read speeds from a physics text and compare them with yours.