My first look at thermodynamics, The laws.

 My current knowledge of thermodynamics is that it is to do with heat energy. I remember the equation E=1/2mc^2 from my GCSE days of physics. I've also watched some documentaries on how physics has changed and among one of these changes was Entropy, from what I understand entropy is the probability of chaos (or the probability of chaos occurring), which can be symbolised by a hot tea cup, when you remove your wrap your hand around the cup your hand warms up. The heat energy of the tea cup has transferred into your hand and if you put your hand on a new surface then the heat energy will leave its mark on the wall. This is an example of entropy, it is defined by the capital letter S and it puzzles physicists to this day.

What i've learnt:

As per every aspect of physics there are laws, in this case there are 4.

Zeroth law, this law states that if two systems that are both in thermal equilibrium with a third system being introduced then they will be in equilibrium. This law was introduced long after the first 3 laws, but it lets you avoid referring to entropy and find the definition of temperature in a non circular way. Hopefully when I return to thermodynamics (and learn about it in school) this law will make more sense.

1st law, this law is the thermodynamics version of conservation of energy. in a closed system we can use the equation ∆U = Q - W. 

∆U is the internal energy of the system.

Q is the heat supplied to the system.

W is the work done by the system to its surroundings.

- This is if there is no matter (mass), if there is matter however we use U(system) = U1 + U2.

U(system) is the total internal energy.

U1 and U2 is the energy from the two systems (in this case it is two, but it can be 3, 4 or however many the question tells you)

As this is a conservation of energy law energy is not created or destroyed only transferred in a closed system.

- However the internal energy has a relationship with temperature as the two are not the same. In the case of thermodynamics if a closed system has pin point temperature then we use E(total) = KE(system) + PE(system) + U(system).

E(system) is the energy of the system

KE(system) is the kinetic energy of the system due to its motion

PE(system) is the energy from an externally applied force (probably gravity as its the most common potential energy)

- If the work done increases then the total energy decreases as the there is energy being transferred out of the system in the form of work, provided no external heat was supplied to the system, this could come from either the kinetic, potential or internal energy systems. 

- If matter is transferred however only the internal and potential energy associated with it are transferred into the new combined system. the equation (u∆M)into the system =∆\U(system)

u is the internal energy per unit of the mass transferred 

∆M is the amount of mass transferred into the system

- The flow of heat is a natural energy transfer of moving from system to system, other than the work done or any interaction with matter. However if the system is one that can let heat come in and out (diathermy system) the energy can be changed by the transfer of energy as heat.

∆U(system) = Q

Therefore the first law of thermodynamic is conservation of energy!

2nd law, if two closed systems interact with each other they will eventually reach thermodynamic equilibrium (with itself, not necessarily with the other system), which are less than or equal to the total entropy of the final combination. Where entropy increases over time so the initial entropy is less than or equal to the final entropy.

- This law is applicable to a variety of process, both reversible and irreversible.

- reversible processes have the equation ∂Q = TdS

∂Q is the element of heat transferred (convection of heat energy).

T is the product of temperatures.

dS is the increases of the systems entropy.

A simple definition of entropy (according to my current understanding) is a physical measure of the microscopic movement of particles in a fixed state.

3rd law - a systems entropy approaches a constant value the closer to absolute 0 it gets.

entropy is related to the possible microstates (arrangement of molecules in an instant) according to Boltzmann constant (1.380649x10-23). the equation S=Kb ln(Ω)

S is entropy

Kb is Boltzmann's constant

ln(Ω) is the number of microstates, specifically Ω as when Ω = 1 ln(1) = 0, therefore at absolute 0 there is only 1 microstate.

overall I have learnt the 4 principle laws to thermodynamics (although only 3 have numbers), this is what I understand:

zeroths law - systems will always end up in equilibrium.

1st law - conservation of energy

2nd law - two or more systems have an initial entropy greater than or equal to the final entropy

3rd law - a systems entropy approches a constant the closer to absolute 0

That's it for today, I will see you again when Deyan's Wild Adventurous returns.