Mechanical energy

In physics, mechanical energy describes the potential energy and kinetic energy present in the components of a mechanical system.

Simplifying assumptions

Scientists make simplifying assumptions to make calculations about how mechanical systems react. For example, instead of calculating the mechanical energy separately for each of the billions of molecules in a soccer ball, it is easier to treat the entire ball as one object. This means that only two numbers (one for kinetic mechanical energy, and one for potential mechanical energy) are needed for each dimension (for example, up/down, north/south, east/west) under consideration.

To calculate the energy of a system without any simplifying assumptions would require examining the state of all elementary particle(s) and considering all four fundamental interactions). This is usually only done for very small systems, such as those studied in particle physics.

Distinguished from other types of energy

The classification of energy into different "types" often follows the boundaries of the fields of study in the natural sciences.

• Chemical energy, the kind of potential energy stored in chemical bonds; studied in chemistry
• Nuclear energy, energy stored in interactions between the particles in the atomic nucleus; studied in nuclear physics
• Electromagnetic energy, in the form of electric charges, magnetic fields, and photons; from the study of electromagnetism
• Various forms of energy in quantum mechanics; for example, the energy levels of electrons in an atom

In certain cases, it can be unclear what counts as "mechanical" energy. For example, is the energy stored in the structure of a crystal "mechanical" or "chemical"? Scientists generally use these "types" as convenient labels which clearly distinguish between different phenomena. It is not scientifically important to decide what is "mechanical" energy and what is "chemical". In these cases, usually there is a more specific name for the phenomenon in question. For example, in considering two bonded atoms, there are energy components from vibrational motion, from angular motions, from the electrical charge on the nuclei, secondary electromagnetic considerations like the Van der Waals force, and quantum mechanical contributions concerning the energy state of the electron shells.