Conservation of Energy and the First Law of Thermodynamics with examples. Energy moves and changes, but the total amount of energy is not changed. The second law explains why we can't re-use the energy over and over.

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The First Law of Thermodynamics with Examples

Our changeable friend energy, with its multiple "personalities", is sometimes hard to keep track of and even harder to define. But it does always behave in predictable ways. This means that if you know the rules you, like engineers and scientists, can often predict what will happen and what won't happen.

Smart scientists and engineers, through clever experiments and even cleverer thinking, figured them out in days gone by. It took some open-minded creative thinking. It was not obvious to anyone back then. And much of what was obvious back then about energy was wrong.
 This section is on the First Law of Thermodynamics, or the Conservation of Energy as it is often called. To start, let's remind ourselves of a few things. A Few things to remember: Energy can be stored. Energy can move from one bunch or piece of matter to another bunch or piece of matter. Energy can be transformed from one type of energy to another type of energy. A wind turbine converts some, not all, of the kinetic energy in the wind into mechanical and electrical energy. The First Law of Thermodynamics says the sum of the energy put into the wind turbine plus the remaining energy in the air after it passes through the turbine, must exactly equal the energy in the wind before it entered the turbine.
The First Law:
During all this moving and transforming the total amount of energy never changes.

That's it! I've done it!
That's the first law of thermodynamics! Ta da!
Energy changes form and moves from place to place but the total amount doesn't change.
Simple, eh?

Other ways to say it:
It's conservation of energy. Energy is conserved during any and every process or transformation or "happening".
Energy doesn't pop into existence from nowhere.
Energy doesn't pop out of existence into nowhere.
Energy is neither created nor destroyed (the old fuddy duddy way of saying it).
"Energy in" equals "energy stored" plus "energy out"
(if no energy is stored, then "Energy in" equals "Energy out").

You may have already heard that the 1st Law says energy is "always conserved". So why are we always saying we need to conserve more energy if it is "always conserved" already? Darn old english language, same word but different meanings. When we say energy is always conserved we mean the total amount of energy in any process or reaction never changes. When we tell ourselves to conserve energy we mean to use less of it by doing things like driving more fuel efficient cars, or insulating our houses better.

But hold on, if energy never goes away, if the total amount always stays the same, why do we have to worry about not wasting it? Can't we just keep reusing it? We don't really "use" energy, we convert it, and it never "get's used up".

It's not a stupid question. It's a very good question. Unfortunately, the First Law of Thermo doesn't really answer it. The popular first law just says the total amount of energy doesn't change.

Scientists and Engineers had to discover a second law of thermodynamics to answer questions like those above. This section is only on the first law but you can jump to the Second Law page now for a very good explanation of the gist of that law, or continue on to the fascinating next page for some good examples to further clarify the First Law. I hope you will read all the pages, for the sake of my fragile ego.

On page two of this section we'll give some examples of the results of the conservation of energy. Click on the Next Page link below.

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The Second Law of Thermodynamics
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