In this program we introduce students to the concept of efficiency, which is a measure of how much useful energy you get out of something compared to the amount of energy that you put into it. We answer a number of questions including: how much light energy do we get out of light globes compared to the amount of electrical energy that goes into them, how much kinetic energy do we get out of cars compared to the amount of chemical energy that we put into them and how do our arched feet make us the long-distance running champions of the animal world? This program is the most energy-efficient way of learning everything that you need to know about energy efficiency.