You're forgetting the law of conservation of energy. If you set an object to spin in a frictionless vacuum with no opposing forces, it will spin forever, but to get it to produce, say, electricity, you must remove energy from the system, thus causing it to slow down.
The spin of the Earth isn't generating any power, so, by Newton's first law, it will continue to spin until such time as it is acted on by an outside force. If we attached a generator to its axis, we'd get quite a bit of electricity up until the day the Earth stopped spinning.
The reason tides affect the spin of the Earth has to do with torque equations. I can't remember torque right now, but the energy of a spinning system is directly proportional to its radius and revolutions per unit time. The tides increase the radius of the Earth. Since energy remains constant, this has a corresponding decrease in the rate of rotation. However, when the tide shifts, the changes cancel each other out and are too small to be noticed. In order to see this principle in action, there are 2 things you can do. The first is to sit in a rotating chair with one weight in each hand. Spread your arms out and then get a friend to start you spinning (or use your foot). Once you are spinning, pull your arms in and you'll notice that you start spinning 'faster.' The other way involves watching figure skating. Watch when one of the skaters is spinning with her leg outstretched, then watch as she pulls it in. She starts spinning really fast.
"Lighght"
- This 'poem' was bought and paid for with $2,250 of YOUR money.
Name one thing the government does better than the private sector and I'll show you something that requires the use of force to accomplish.