Raven stretches a rubber band between two fingers. "Ready?" she asks.
She lets go of one end. The band snaps back and flies onto the couch cushion.
Rocket pulls the band back further this time. It flies even farther.
"What do you notice about how far you stretch it?" Raven asks.
Nova hovers over the couch. "My hint," she says. "Stretching put energy in. Letting go let it out. Compare a little stretch with a big one."
Stored energy is energy waiting to be used.
A stretched rubber band and a squeezed spring both store energy.
A battery stores energy too. So do food and fuel.
People often say a device produces energy. They really mean it converts stored energy into a form we want.
A flashlight converts the battery's stored energy into light. A wind-up toy converts its spring's energy into motion.
| Statement | True or false? |
|---|---|
| A stretched rubber band stores energy. | ? |
| A battery stores energy. | ? |
| A flashlight makes new energy from nothing. | ? |
| Letting go of a stretched band converts stored energy into motion. | ? |
A little stretch stores a little energy. A big stretch stores more.
More stored energy means more energy to convert into motion.
That is why Rocket's bigger stretch sent the band farther.
Engineers use this idea when they design toys and machines.
You understand stored energy now. Tomorrow you build a roller that rolls back to you!