Raven lays two printed tables beside the landing pad. One lists ways people soften a stop. The other lists units.
"Padding, air bags, parts that crumple, bending your knees," Rocket reads. "They all make the stop take longer."
"What do you notice about our pad?" Raven asks. "Which of these is it most like?"
"Padding," Rocket says. "But I want to add a towel roll and make it thicker and wider."
Nova hovers between the tables. "Two changes at once," she says. "How will you know which one worked?"
Rocket sighs and picks one. "Thicker. Just thicker. Then test." Raven smiles and turns to a clean page.
A college physics text describes everyday ways to make a stop take longer, so the force is smaller. Here they are as a table.
| Everyday soft stop | What it does | From the text |
|---|---|---|
| Padded dashboard and air bags | let the stopping force act over a much longer time | the force to stop a person is much less if it acts over a larger time |
| Car parts that crumple | make the collision take longer | a longer collision time means the force on the car is less |
| Rolling after a jump | extends the time the ground pushes on you | landing stiff-legged on a hard surface makes the force on your legs immense |
| Landing with a parachute | extends the time over which the force acts | the same idea as rolling after a jump |
The National Institute of Standards and Technology describes the SI, the international standard for measurement. Your report uses three of its base units.
NIST also lists derived units such as metres per second for velocity. Your speed numbers from week 1 used that unit.
| Quantity | SI base unit | Symbol | Where it appears in your report |
|---|---|---|---|
| Length | metre | m | drop height, bounce height, stop distance (in centimetres, hundredths of a metre) |
| Time | second | s | how long a stop or a flight takes |
| Mass | kilogram | kg | the ball and the car, if you weighed them |
Pick one change to your pad: thicker filling, a softer top layer, a wider tray, or a rolled rim.
Predict what the change will do to the bounce height or the stop distance. Write the prediction before you touch the pad.
Make the change. Run the same fair test: same drop mark, same ball, same ramp, three trials each. Record the middle values.
Compare the new numbers with yesterday's. Did the change help, hurt or do nothing? All three are real results.
| Test after one change | Trial 1 | Trial 2 | Trial 3 | Middle value | Better than yesterday? |
|---|---|---|---|---|---|
| Drop on changed pad: bounce height (cm) | |||||
| Roll on changed pad: stop distance (cm) |
| Statement | True or false? |
|---|---|
| Changing two things at once makes it hard to know which one worked. | ? |
| A change that makes the bounce higher is a useless result. | ? |
| The second test should use the same drop mark as the first. | ? |
| The SI is the international standard for measurement. | ? |
Careful iteration. Tomorrow you write it all up: the Sports Physics report.