A hardware-store display has a long spring hanging from a hook. Vada stretches it down by 4 cm and holds it there. Easy.
She stretches it down by 8 cm and holds again. Noticeably harder.
Same spring, same hand, two holds. Why is the 8 cm hold harder, and is there a pattern in it?
Hold the spring stretched by 4 cm: it takes some force to keep it there.
Hold the same spring stretched by 8 cm: it takes a greater force.
Try 12 cm: greater still. Every extra bit of stretch raises the force needed to hold it.
The pattern runs both ways: ease the stretch back from 8 cm to 4 cm, and the force needed drops.
This is a prediction tool. Before touching a spring, you can say which hold will need more force: the one with more stretch.
Yael holds a garage-door spring stretched by 2 cm, then by 6 cm. Which hold needs the greater force?
Wells holds a screen-door spring stretched by 3 cm, then by 9 cm. Which hold needs the greater force?
The spring is the same; only the stretch differs.
More stretch needs more force to hold.
9 cm is the greater stretch.
The 9 cm hold needs the greater force.
Xenia lets a stretched exercise spring ease back from 10 cm of stretch to 5 cm, holding it still at each stage. What happens to the force she needs?
The stretch is shrinking from 10 cm to 5 cm.
Less stretch needs less force to hold.
The pattern runs both ways.
The force Xenia needs drops as the stretch eases back.
Wells slowly stretches a spring farther and farther, pausing to hold it still at each stage. What happens to the force he needs at each later pause?
Two holds of one trampoline spring are planned: a 5 cm stretch and a 1 cm stretch. Before touching the spring, what can be predicted?
How much more force a given stretch needs is the next lesson's question: it leads to a number for each spring.
A bike-rack spring is held stretched by 3 cm, and later by 7 cm. Which statement is right?
A keychain spring is held stretched by 4 cm in the morning, and by 4 cm again in the evening. Compare the forces needed for the two holds.
One drawer spring is held at three stretches in turn: 2 cm, 9 cm, and 5 cm. Which hold needs the greatest force?