## Physics Questions People Ask Fermilab

Hello,

I am so happy to visited your site It was full of answers to my questions!! So, I have a question about thermal Energy...We have some kind of energy in the world. electric energy, electromagnetic energy, gravity energy and thermal energy and we know that other energies are combination of these energies. So, we can suppose these energies depended on a fields.for example electric energy is created by electric field and we can divergence from this field becouse it is vector field but for thermic energy we can not suppose any vector fields and we can not depend it to any vector field. Butt in end we named all of these as "Energy" Please explane for me that is thermic energy exactly an energy? and if "YES" Why we can not depend it to any vector field?

Dear Amir,

I am glad to hear that you liked our website. Thank you.

Is thermal energy exactly an energy like electromagnetic and gravitational energy? Why is there no vector potential associated with thermal energy?

Thermal energy is a form of energy, but it is quite different from electromagnetic and gravitational energy. Thermal energy is based on the TEMPERATURE ( corresponds to MOTION) of particles, whereas the other two forms of energy are based on FORCES between two objects.

To use thermal energy, you need a temperature difference, say a container with hot water and a container with cold water. Then you can design a machine to use the energy difference to do some work. It is the temperature that determines the amount of thermal energy of a system. Temperature is not a vector but just a simple number, also referred to as a scalar field. Correspondingly, there is no vector potential. A thermal potential map would be just a map with dots and a single number next to each dot: the temperature. Based on such a map you then can draw vectors in the direction that heat would flow. Those vectors would indicate temperature gradients. At the microscopic level, thermal energy can be explained by the motion of atoms. Take water: it consists of H2O molecules. At low temperatures, all molecules line up and build a crystal: ice. At higher temperature, all molecules start moving: the molecules vibrate. If there is enough energy, the molecules will start to move freely: the ice melts. If you transfer more and more heat, the molecules move faster and faster. Eventually, some will move fast enough that they can leave the liquid: water vapor can be seen on the surface. If all molecules are moving very fast, the water being very hot, the water turns into gas.

The theory behind this picture is called BROWNIAN MOTION. The average speed of the microscopic particles is used to explain the temperature, the pressure and many other properties of the material.

Electromagnetic and gravitational energy are based on forces between particles or objects. A force is determined by its strength and a direction. Hence it is a vector property. Force fields always have an associated vector potential, from which one can derive the exact value of a force for any given point. Example: from earth's gravitational potential I can calculate the force that acts on me when I am in various places: at sea level, on top of a mountain, in an airplane, somewhere in outer space.

Electromagnetic and gravitational forces are based on the properties of the particles/objects, not their motion. For the two cases mention, the strength of forces and potential fields are determined by the amount of electric charge and the amount of mass involved, respectively.