Nuclear Physics
The Liquid-Drop Model
Who thought when starting this unit we'd be learning about nuclear physics? We didn't, so it's all good.
We've learned that matter is made of atoms. Atoms are made of particles. What and where are those particles?
The three principle particles of an atom are its orbiting electrons (with a negative charge), neutrons (guess what, they're neutral), and protons (protons are positive). Since they live in the nucleus, neutrons and protons are called nucleons. The nucleus needs a lot of energy to make sure it doesn't fall apart. We call this nuclear glue "binding energy."
It doesn't quite happen like this, but for the sake of clarity, we like to think of the atom as a simplified solar system. The Sun is the nucleus, which is made up of nucleons, and the planets are identical electrons. Electrons orbit the nucleus.
The nucleus is positively charged. How do we model that?
Nuclear physicists have come up with two kinds of models, and both work: the shell model and the liquid-drop model. Since we are studying a module on fluids, let's stick with the liquid-drop model.
The liquid drop model assumes a few basic things: a constant density, a size proportional to the number of nucleons, and a binding energy that varies depending on the mass of the nucleus, which makes sense. We'd need a larger nucleus to house more nucleons, and more nuclear glue if the nucleus is bigger. A constant density implies the effects of all the nucleons average out throughout the nucleus. Is this starting to sound familiar?
Yep, sure is. This sounds exactly like a drop of water. And yes, we totally knew that.
Just like a drop of water, the particles within a nucleus can also vibrate, rotate, and change shape as long as its volume is constant. A drop of water has a constant density and is larger with more molecules. Remember what heat of vaporization is? In a way, it's exactly like binding energy. We'd have to provide a drop of water a certain amount of heat to break it apart into gas.
In the case of a nucleus, we'd have to do exactly the same but to break it apart, we'd have to conquer its binding energy. It doesn't matter how this energy is provided and in what form because energy is energy. All that matters here is that the amount needed to break apart the nucleus is equal to its binding energy.
We weren't lying when we said fluids are everywhere. What's even cooler is that the way we deal with them can be applied to multiple topics in physics, even more than the ones we've talked about thus far.