Thermodynamics is a pretty big word, but its meaning is really simple actually. It really has a lot to do with heat and its relationship with other types of energy. Thermodynamics connects to measuring as well, measuring energy that is. One type of energy that it is involved with is thermal energy, it is the energy that a system or occasional substance has because of its temperature.
One of the most popular properties of matter that is involved with thermodynamics is heat. When energy is transferred from one thing to another, the cause being temperature, that is the energy of heat. Heat is a very flexible type of energy, it can be changed into other forms of energy and back, can be moved to different places, yet it cannot be created or destroyed. A steam turbine is an example of this, it can morph heat into kinetic energy to run a generator, a generator that changes kinetic energy to electrical energy. Using a light bulb can turn the electrical energy, into light/electromagnetic radiation that when absorbed into a surface can be return back to its original form as heat.
Heat is very dependent on the speed and amount of atoms and molecules when they are in motion. The faster that they move, the higher the temperature will go, and the larger quantity of atoms and molecules in motion, the greater amount of heat they give off. Temperature is classified as a sample of sorts, a sample of the larger amount of temperature measured. Specific heat is known as the total amount of heat needed change the temperature of a certain object or substance. Thermal conductivity is different, it is the speed in which heat moves through a certain piece of material, it is shown as the amount of heat shown per unit time. Heat is a very interesting thing, it can be moved and transferred around, it is called heat transfer.
Heat transfer can come in three forms; conduction, radiation, and convection. Conduction is energy moving through a solid object/material, it happens when bodies are in direct contact, like when you hug someone. They give you their heat and you give them yours. Radiation is when electromagnetic energy is given off or it is absorbed. Convection is a movement in heat through fluids, when the molecules come in contact with a solid they move the heat, or they transfer it.
All thermodynamic systems give off waste heat, and this waste heat is increasing the amount of entropy. Entropy is the amount of thermal energy not able to do any work. When entropy is in any closed system, it always increases, never decreases.
The third law of thermodynamics says that entropy always has a positive value, never a negative one.