Have students fold origami jumping frogs using green index cards (the color really doesn’t matter, just makes it more fun). Allow students to play with the frogs and have them explain at which point the frog possesses 100% potential energy and at which point it possesses 100% kinetic energy.
Make sure you try your hand at making the frogs before presenting this lesson to your students. It's not hard to do, but you'll be much more effective at helping students if you've done it yourself first!