# B Thermal vs Internal energy

1. Mar 20, 2016

### TT0

What is the difference? I read that thermal energy includes both kinetic and potential energy but isn't that what internal energy is?

Cheers!

2. Mar 20, 2016

### John Pang

I think there are actually no differences between the two terms. Both internal energy and thermal energy of a system refers to the sum of KE and PE, and both are primarily determined by the collisions and interactions between the atoms and molecules in the system.
However, internal energy should be a more general term than thermal energy. In terms of thermodynamics, the term thermal energy would be used to replace tge term internal energy.

3. Mar 20, 2016

### John Pang

It is just a matter of definition. Thermal energy is primarily defined as the internal energy of a system. Then, thermal energy can be referred as a form of internal energy.

4. Mar 20, 2016

### drvrm

In thermodynamics , thermal energy refers to the internal energy present in a system due to only to its temperature.

It is often most convenient and precise to think of heat as the transfer of energy,
Heat and work depend on the path of transfer and are not state functions, whereas internal energy is a state function.

Internal energy is defined as the energy associated with the random motion of molecules.

It is separated in scale from the macroscopic ordered energy associated with moving objects; it refers to the invisible on the atomic and microscopic molecular scale.

An example- a glass of water sitting on a table at room temperature has no apparent energy.
. But on the microscopic scale it can be seen as mass of high speed molecules traveling at hundreds of meters per second.
If the water were tossed across the room, this microscopic energy would not necessarily be changed when we superimpose a large scale motion on the water as a whole. so it is state function .

see wiki/hyperphysics site for a discussion.<http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/inteng.html> [Broken]

Last edited by a moderator: May 7, 2017
5. Mar 20, 2016

I see thanks