Rocket has three stacks of books on the patio: one book, two books, three books. One cardboard ramp leans on each in turn.
"Higher start, more stored energy, longer roll," he says. "Let me do all three at once."
Raven holds up the tape measure. "One at a time. Three rolls each. Same ball, same release, only the height changes."
Nova hovers above the one-book ramp. "What will you measure, the speed or the distance?" she asks.
"Distance is easier," Rocket says. "Where it stops."
"And the time to cross one metre," Raven adds, setting the kitchen timer. "Then we know the speed too."
The ball leaves the lowest ramp and rolls a short way. Rocket looks almost disappointed.
"What do you notice?" Raven asks. "Save the excitement for three books."
Today you store different amounts of energy by lifting the same ball to three ramp heights, then measure what that energy does.
You measure how far the ball rolls and how long it takes to cross a one metre stretch at the bottom.
This follows a take-home investigation in an OpenStax college physics text, which rolls a marble down a ruler propped on a book.
| Ramp height | Time for 1 metre (seconds) | Speed (metres per second) | Roll distance (cm) |
|---|---|---|---|
| One book, roll 1 | |||
| One book, roll 2 | |||
| One book, roll 3 | |||
| Two books, best roll | |||
| Three books, best roll |
The physics text says it this way. When friction is small, the kinetic energy at the bottom is proportional to the potential energy at the release point.
Lifting the ball higher stored more energy. That energy became speed at the bottom, and the speed carried the ball farther before friction stopped it.
Your three rolls from one height should be close. If one is far off, the ball may have bumped the ramp edge.
Timing by hand is rough, so your speeds are estimates. The pattern across the three heights matters more than any single number.
The ball never rolls forever. Friction and drag turn its kinetic energy into warmth, and it stops. That is next week.
| What the lab shows | True or false? |
|---|---|
| The three-book ramp stored the most potential energy in the ball. | ? |
| The ball from the one-book ramp should roll the farthest. | ? |
| More stored energy at the top meant more speed at the bottom. | ? |
| The ball's energy came from a push, not from its height. | ? |
Careful measuring. Tomorrow you will read the gravity of other worlds and work out where lifting a ball stores the most energy.