Most of us love the dear old Earth – in fact we’re quite attracted to it. That attraction arises from the Earth’s large mass and thus the Earth’s pull of gravity. When we lift a book away from the center of dear old Earth, we do work on that book. We do work because we must counteract the book’s attraction to the Earth in the process. We do work by applying a force over a distance. What does that do for us? Well, it tires us. The book, however, gets energy out of the deal. Any time work is done on an object the energy of that object is changed. Doing work on an object, or having the object do the work, results in a change of energy. Sometimes work results in changing an object’s potential energy, kinetic energy, or possibly both types of energy. Power is the rate at which work is done. If you lift a book quickly, you operate at a higher power level than if you lift a book slowly. Work and energy are measured in joules (J), while power is measured in watts (W).
Students will calculate the work done against gravity and the level of power needed to walk up a flight of stairs. Students will then compare the work and power of walking to running up the same stairs.