Science Buddies: "Ask an Expert"

If the moon's gravity produces tides by moving water, and that kinetic energy can be converted to electricity, and if energy cannot be created or destroyed, what is losing energy in order to add kinetic energy to the water in the ocean? The moon doesn't seem to be losing any energy. It's not falling out of its orbit. Where is the exchange of energy that should be happening to prevent power generators that use ocean tides from being perpetual motion machines?

The Ask the Expert forums are for students in Grades K-12 (and their parents and teachers) who are doing hands-on science projects. If you are a student and you are doing a hands-on science project, please provide details about your project, including your hypothesis and your plans for conducting experiments to test the hypothesis. Otherwise, there are other sites on the web where your questions would be more appropriate. Thank you.