OK, it's Monday, not Friday, but last week's Science Friday video is too cool to skip.
Without further ado...
Science FridayCourtesy Science Friday
"Maxwell von Stein, a 22-year-old graduate of The Cooper Union, built bicycle that uses a flywheel to store energy. Instead of braking, Max can transfer energy from the wheel to the flywheel, which spins between the crossbars. The flywheel stores the kinetic energy until Max wants a boost, then he can transfer the energy back to the wheel using a shifter on the handlebars."