Energy is possibly the most basic and yet the most complex topic that exists in science, and is an area in science where I find the definitions a little slack, although I have no better ones. This post is intended to serve as a brief discussion around some points of interest to me. You will not find it a comprehensive overview of everything you need to know about energy. Instead you should see it as a collection of points that are often overlooked.
We often define energy as the ability to do work, but then we define work as the application of a force over a distance; which is the energy transferred to the object. This feels a bit like opening a dictionary and looking up energy and reading see work then looking up work and seeing energy transferred. I am being picky here – but my point is they are not great definitions when they create a circular reference. What I find in science is often the most mundane things are the hardest to define; and in actuality some of the more complex ideas, say the interchangeability of mass and energy are very easy. Of course this isn’t a rule that always holds water – it is just a general observation that I find to be true much of the time.
One thing that really irks me is that not enough time is given to the fact that all energies are roughly the same thing in one form or another, which is why it is appropriate to measure the thing in Joules all the time! Think about it… you can use the same unit for kinetic energy as you can for internal energy. This should make the curious student think. The reason is it all comes back to forces, work and fundamentally the same type of energy – the same thing classified in a different way. Let us illustrate a couple of examples. Say you have what is taught in school as the energy of heat and the energy of motion – kinetic energy and thermal energy. Now how different are these things? Well not really at all. All internal energy comprises of is increased vibration or motion of the particles within the substance. When a hot object is placed into a cool tank of water, the cooler atoms and the hotter atoms collide giving the cooler atoms more kinetic energy and the hotter atoms less until they reach an equilibrium point. So what we can see here is that internal energy is analogous to kinetic energy on a smaller scale. Similarly electrical energy is essentially the flow of electrons – electrons with kinetic energy. I am not saying everything is an exact direct relationship like the ones I have outlined, however with some creative licence you can get there.
Another thing is electromagnetic radiation – or energy in the form of say light. The thing about electromagnetic radiation is that it is so so central to Physics; why do they leave it so late to bring together all the good ideas!? Electromagnetic waves are simply regular disturbances in electric and magnetic fields that transport energy from one place to another. On the most basic level; that is it. X-rays, gamma rays, infrared, ultra-violet, visible light, radio – all the same thing. Look at it like this; an electromagnetic wave is one type of wave that can be defined by some certain features; the speed of propagation, the wavelength, the frequency and the amplitude. The speed does not change for any electromagnetic wave (c in a vacuum) so that leaves us just three. So all of these different electromagnetic radiation sources you know of – all you need to do is take your one familiar wave, and understand the wavelength, amplitude and frequency then you can put a label on it. Appreciating this allows you know why for example something might be defined as both a radio wave and a micro wave.. they are not different waves or anything overly special; so as you increase the frequency and decrease the wavelength you start to transition from radio wave to microwave – a blended scale.
Finally, I think that we cover the equivalence of energy and mass at a date that is far far far too late and it is so important. Energy = mass and mass = energy. Plus because it is the most famous equation in physics (E=mc² I mean) it really hooks kids in. It makes you feel like you are doing the good stuff so early on. Discovering this, well that takes genius. But once it is discovered you can apply it to unlock the secrets of the atomic bomb, nuclear reactors.. you can understand why the sun gives off energy. But it is more that this in truth – it allows you to more fully appreciate what energy actually is. If you have mass you have energy stored within it, but on the other hand if you have energy you can create mass. You cannot destroy or create energy – why? Well one way of looking at this is to say any process where we might be able to create energy we would need something of mass to do this and if we were going to create something of mass we would need energy. They are the same thing. This isn’t 100% concrete, you could argue that you might be able to create more energy from a little mass etc – but experiments show you cannot.
That is the end of my ramblings on energy for today I think! Have some equations on energy to finish. Any questions – hit me up.