Now here is a law of importance! With far reaching consequences, the First Law of Thermodynamics is nothing less than an expression of a much wider concept: The Conservation of Energy.

That is, as you may be aware, energy cannot be created or destroyed… thank heavens, if it could then physics would be a much harder science! Energy can only change form, ‘converted’ is the word in popular use (and yes, matter can be considered a form of energy too).

This leads to the simple, yet powerful, statement of “The total energy of the Universe is always the same”!

The first law of thermodynamics is normally expressed in equation form, but essentially it means something like:

The increase in the internal energy of a system is equal to the amount of energy added by heating the system, minus the amount lost as a result of the work done by the system on its surroundings.

As usual, definitions are wordy things, but if you untangle this one then you will see that the increase in energy is simply the energy added minus the energy taken away. Blindingly obvious, right?

Indeed, but only if you accept the fact the system itself does not at any point create extra energy or destroy energy (conservation of energy is assumed), which is itself not nearly quite so obvious.

What does it mean?

Unfortunately it means that you cannot get something for nothing! You cannot get out of a system more energy than you put in; likewise, you cannot take from a system more energy than it has.

This might seem like common sense, it does to me; but I look at the world through the pessimistic eyes of a human (well not just any human, me in fact!). It is a shame that the Universe actually works this way though…

Alas, it gets worse: not only can you not get something for nothing; you can’t even convert energy at 100% efficiency! More next time, on the Second Law!