Internal Energy Formula – Definition and Examples

Energy exists in various forms, including thermal, mechanical, kinetic, potential, electric, magnetic, chemical, nuclear, and more. In the realm of thermodynamics, it is recognized that these diverse forms of energy collectively constitute the total energy of a system. This total energy can be categorized into two main groups: macroscopic and microscopic.

Macroscopic forms of energy refer to the energy a system possesses as a whole concerning some external reference frame. Examples of macroscopic energy include kinetic energy (related to motion) and potential energy (related to the system’s position or elevation in a gravitational field). These macroscopic energies can be influenced by external factors such as gravity, magnetism, electricity, and surface tension.

Internal Energy – Examples

On the other hand, microscopic forms of energy are associated with the molecular structure of a system and the degree of molecular activity. Importantly, these microscopic energies are independent of external reference frames. The collective sum of all these microscopic energy forms constitutes the internal energy of a system, denoted as U.

In a more specific breakdown, kinetic energy (KE) pertains to the energy resulting from the motion of a system relative to a reference frame. Potential energy (PE) is the energy a system possesses due to its elevation in a gravitational field. When external factors are not significantly affecting the system, the total energy (E) of the system can be expressed as the sum of kinetic, potential, and internal energies:

E = KE + PE + U

In this equation:

• “m” represents the mass of the system.
• “v” represents the velocity of the system.
• “h” represents the height or elevation of the system from a reference point.
• “U” signifies the internal energy of the system.

It’s important to note that for stationary closed systems (where there is negligible change in kinetic and potential energies), any change in the total energy (ΔE) is equal to the change in internal energy (ΔU).