Thermodynamics is basically anything dealing with heat and the motion of particles on a very small level. We define temperature as the amount of energy that exists in the movement of the particles in a substance. When something is hot, it has a lot of energy. If it is cold, it has little. So let us define some temperatures.
Most people are familiar with Fahrenheit but most physics donít use it. Instead, they use either the Celsius scale or the Kelvin scale. The Celsius scale is based on water. Zero is when it freezes and 100 is when it boils. The Kelvin scale is based on absolute zero. At zero Kelvin, there is no thermal energy inside an object. Zero Celsius is about 273 Kelvin. Sounds hot but it isnít.
Law 0-All objects attempt to reach thermal equilibrium.
Thermal equilibrium is when two objects next to each other are at the same temperature. If one was hot and the other cold, they reach equilibrium somewhere in-between those two temperatures.
Let us describe heat as some quantity, Q, and everything else as it usually is. It has been observed that when energy is transferred through conduction (heat going from object a to object b), there is an exact equation relating this:
Q = mcDt
Here, the c is a constant that depends on what the object is. That number is the specific heat of the object. The Dt (delta t) is the change in temperature. If we have two objects that are in contact but have different temperatures we can say:
m1c1Dt1 = m2c2Dt2
If we know the initial temperature of each, the mass, and the specific heat, we can find the final temperature by simply substituting Tf- Ti for Dt for each change in temperature. We get:
m1c1(Tf1- Ti1) = m2c2(Tf2- Ti2)
Replace the variables with what you know and solve! Itís that simple.
But, it has been observed, something different happens when things melt or freeze. In order for an object to go from being a liquid to a gas, a lot more energy is needed to get the molecules to fly out of the substance. The equation for that is:
Q = mL
Where L is what is called the latent heat of fusion. It is another constant that depends on the substance and if itís freezing or melting (or both!).
Law 1-All energy is conserved inside a closed system.
If you could seal all the energy inside a box, none of the energy would escape, correct? So the energy is said to be conserved in that box. That is basically all that law describes.
Law 2-Entropy-As energy is transferred from one thing to another inside a system, the system becomes more disorganized.
Some may call this law the law of death. As energy is transferred from one thing to another, the disorder increases. This doesnít matter though when the overall temperature of the system is in the millions of degrees because it is already messed up, but when you have reasonable temperatures the entropy increases at a higher rate.