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 bounces back to its original shape after hitting a surface determines how many times it keeps bouncing. To compare this across tennis ball brands, drop five balls of each brand from one meter and count the bounces. More bounces mean the material returns to shape more completely after each impact — greater elasticity. Then launch the same balls from a tennis ball launcher on an open field and measure how far each one travels. Softer balls, with their higher elasticity, bounce more and tend to fly farther from the launcher.
Different golf ball brands spring back to shape with different levels of efficiency. To rank them, drop each brand from one meter onto a flat surface and count the bounces — more bounces mean more elasticity. Then bring three amateur golfers to a driving range and measure how far each ball travels when hit with a driver. Comparing the bounciness rankings to distance measurements shows whether the springiest ball really does fly the farthest.