conservation of energy

You'll have to do it yourself probably,I did.use CR4 search..type in Hyperphysics.Lots of homework here.

One practical use is of exposing perpetual motion and free energy claims. Recenly there was everwatt generator violation example. See link for brief about law.

http://en.wikipedia.org/wiki/Conservation_of_energy

The law of conservation of energy states that energy can neither be created nor destroyed. In other words the total of all energies in a closed system is constant and can't be varied.

What dose this mean? Well for example if you were to pump 1,000 liters of water up to a tank that was 100 m above the ground you would need to add energy to this water and the energy that you add is proportional to the mass of the water, the height you raise it and the force of gravity. Mathematically it can be stated as

Energy_Potential = Mass x Height x Gravity

Or more commonly

PE = mgh

So in this case

Energy_Potential = 1,000 x 100 x 9.81 = 981,000 Joules = 981 Kj

That means if we were to use an electrically powered pump to pump the water it would consume 981 Kj of electrical energy.

Now if we were to run this water back down and run it through a hydroelectric generator and generated electricity again we could only get back 981 Kj of electricity. In other words the energy has been conserved.

In reality however no machine is 100% efficient and some of the energy is consumed in friction, electrical resistance etc. The result is that the initial pump would consume more energy than the 981 Kj that is required to pump the water up. The additional energy isn't lost it must go somewhere and it usually turns up as heat. On the way back down the generator will also not be 100% efficient and so we will get back less than the 981 Kj that the water had with the difference again usually ending up as heat.

The upshot of this is that because no machine can ever be 100% efficient you can never make a machine that will work for ever. No matter what you do the energy will slowly drain away and the machine will stop working.

I hope that helps.

Hmm, maybe this should be appended to indicate mass-energy, since energy can be translated into and from matter.

There is another law called the conservation of matter but the two are interrelated. What you say is true and matter can be converted to energy and is in a nuclear reactor according the Einstein's famous equation E = mc² . It's open to debate but one could say that matter is just a particular manifestation of energy. If the big bang theory is correct then all matter was at one stage energy and as the universe expanded the matter condensed out.

At any rate unless you start talking about nuclear fission of fusion the law applies and even then they are interrelated.