Standing on the edge of Niagra Falls you can watch the water pour over. Falling down the gravity of the earth, it exchanges its potential energy for kinetic energy by picking up speed. Some of that energy is extracted by turbines and lights the homes and businesses of Yankees and Canucks alike. Some of that energy is used to pump water up into water towers to maintain the water pressure which those same people use to cook and clean.

Move with a gravitational field, get energy. Move against it, lose energy.

Now let’s say you wanted to take apart the earth. Yes, the whole thing. You want to grab each bit of dirt and pull it out of the earth’s gravity and move it out to deep space. How much energy in total would it take? There’s some practical reasons for wanting to know. The engineers who built the Death Star would need for their superlaser to deliver at least that much energy. And what could be more practical than that?

Read More: http://scienceblogs.com/builtonfacts/2009/02/the_physics_of_the_death_star.php

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