Elasticity
Elasticity is how well a material bounces back to its original shape after being squeezed or stretched.
A rubber band around a jar stretches when you pull it. Let go, and it snaps back to its original size. That snap-back is elasticity. A stiff rubber band has high elasticity. A worn-out one that stays stretched has low elasticity.
Explaining elasticity by grade level
Drop a tennis ball on the ground. It squishes flat for a moment, then pops back round and flies up. The ball goes back to its old shape on its own. Some balls spring back more than others, and those ones bounce higher.
Projects that explore elasticity
How well a ball returns to its original shape after hitting a surface affects how it bounces. You test three brands of tennis balls with different hardness levels. Drop five balls of each brand from one meter and count the bounces. More bounces signal a softer, springier ball. Softer balls bounce more, and they tend to fly farther from a launcher too.
When a drumstick strikes a snare drum, it bends slightly on impact and then snaps back. This project tests four materials: titanium, aluminum, hickory, and oak. A pulley and weight system strikes each drumstick against the drum with equal force, and a video camera records how high each one rebounds. The wooden sticks, hickory and oak, bounce higher than the metal ones.
Not all golf balls spring back from impact the same way. To compare, you drop three brands from one meter onto a flat surface and count the bounces. Then three amateur golfers hit the same balls at a driving range with a driver, and you measure how far each one travels. Comparing bounciness rankings to distance measurements shows whether the springiest ball really does fly the farthest.