The Heat of the Moment

This one is very basic, but delves into one of the most fundamental concepts in all physics.

Energy.

We have all heard that word, but what does it mean, really?

For Physics fans, the word "energy" means "the ability to do something else".

For all others, it may mean "something to keep you going".

Both are correct.

To actually understand what "energy" is, though, a journey into how the word came about may be in order.

Way back when science was fairly young, but there were thinkers with labs (1800-1900 will do), they investigated heat and what it did. They discovered that in general, the hotter something was, the bigger it got (expansion) ( Due to something called the Lennard-Jones 6-12 potential, but that is beyond the scope of this post )

So, what was heat? Well, by careful experiments , a lot by Lord kelvin, they found out that if you cooled something down, the heat would go somewhere else. They also found that you could actually convert mechanical movement into heat AND BACK again. ]

They did a collective "Hmmmm", and the idea was born that there must be something that cannot be created or destroyed, but only converted. They called this the more general name of "energy".

There are many different types of energy, but all are equivalent and interchangeable. You have kinetic energy (from movement), potential energy (from position), but the most common one is known as heat. Heat comes about by something jiggling the atoms in a thing. The more hot it is, the bigger the jiggling, and if the jiggling is larger, the things expands because the atoms need more room to jiggle.

Ok, so that's heat. Movement in other words, but then again there are different types of movement. Travel in a car is one of the best examples. We say the car has "kinetic" energy because it is moving. Where does this energy come from? Again, the car is one of the best examples of energy conversion.

What makes it go? Why, the gas, of course. Gas has energy tied up in the long hydrocarbon molecules ( a molecule is simply two or more atoms bound together chemically )So what does the engine do?

Well, you put the gas in, and inside the car, a piston squashes the air/gas mix, and when done, a spark makes a bang in it. This bang is a small explosion and releases energy from the chemical bonds and this "internal combustion" is powerful enough to push the piston down very hard in it's tube. So now the piston has converted the energy of the bang into kinetic energy.

The piston is attached via a gudgeon pin and this pin converts the linear energy (straight line) to rotational energy of the crankshaft. The downward motion of the piston has now been converted to a spinning motion. But how does this spinning motion get to the wheels? Engines come in two basic types, depending on the relative orientation of the crankshaft (the spindle that gets the energy from the piston) and the drive shaft ( the spindle that drives the wheels). They can either be parallel or at right angles. The part that connects these two spindles is called the "differential".

So, we have now converted the piston energy to the crankshaft energy, and now the differential converts this energy to the drive shaft.

Not finished yet! The drive shaft turns the wheels and the wheels trundle the car along. However, the wheels only move the car because the rubber on the tyres stops the wheels slipping. This is called "friction" and is a major source of energy loss. Hang on! LOSS? But didn't I just say that energy cannot be destroyed? Yes, I did and when I say "lost" I really mean "lost from the source of the energy" ie the gasoline.

So where does it go? Well, as intimated, energy has lots of forms, and the lost energy is lost as sound energy, friction energy, and believe it or not, heating of the road, heating of the rubber, and worst of all, energy is even given to the earth to increase it's rotation! Ok, Ok, so that effect is very small, and may not even be measurable, but it is there.

In all, the internal Combustion Engine is very inefficient, in other words, you can never get all the energy from the gas, and in fact, it is impossible even in principle ( this is called the 2nd law of thermodynamics - see next post)At most, cars only get about 15% of the energy available from the gas. It's a bit like travel. You cannot convert ALL your cash to a different currency, because the exchange people take commission.

In a car, lots of processes take commission. Lets' list some places where energy is lost:

1. Friction inside the supply pipes that bring the gas to the piston.
2. Friction inside the piston.
3. Inefficiency of the combustion.
4. Friction between piston and crankshaft.
5. Friction between crankshaft and differential.
6. Friction between differential and driveshaft.
7. Friction between driveshaft and wheel.
8. Friction on the road.

As can be seen, energy is a complicated business.

As an exercise, try this. A light bulb is held at arms length and released. There are two main energy processes, what are they?

PLUS - how many more subsidiary energy processes can you figure out (hint - think of the car above)? There are at least four!