Mechanical energy is the energy sum in a system or any group of objects which interact on the basis of the mechanical principles. It includes both a kinetic, and potential type of energy. Gravitation, as a rule, is the only external force which has to be considered in this case. In the chemical system of force of interaction between separate molecules and atoms also have to be taken into account.
Mechanical energy of a system exists in a kinetic and potential look. Kinetic energy appears when an object or a system begins to move. The potential energy arises in interaction of objects or systems with each other. It does not appear and does not disappear completely and, often, does not depend on work. However it can pass from one form into another.
For example, a sphere for bowling, being at the level of three meters above the ground, has no kinetic energy because it does not move. It has a large amount of potential energy (in this case, gravitational energy) which will be transformed to kinetic if the sphere begins to fall.
Acquaintance to different types of energy begins in middle school of school. As a rule, it is easier for children to visualize and to easily understand the principles of mechanical systems, without going into details. The main calculations in such cases can be made without use of difficult calculations. In the majority of simple physical tasks, the mechanical system remains closed and factors which reduce value of the general energy of a system are not taken into account.
Mechanical, chemical and nuclear energy of a system
There is a set of different types of energy, and sometimes, maybe, it is difficult to distinguish one of them from another correctly. Chemical energy, for example, represents result of interaction of molecules of substances among themselves. Nuclear energy appears during interaction between particles in an atomic nucleus. Mechanical energy, unlike others, as a rule, does not consider molecular structure of an object and considers only their interaction at the macroscopic level. This approach is intended for simplification of calculations of mechanical energy of complex systems. Objects in these systems usually are considered in the form of uniform bodies, but not as the sum of billions of molecules. Calculation of both kinetic, and potential energy of one object is a simple task. Calculation of the same types of energy for billions of molecules will be extremely difficult. Without simplification of details in a mechanical system, scientists would have to study separate atoms and also all interactions and forces existing between them. This approach, as a rule, is applied in physics of elementary particles.
Mechanical energy can be transformed to other types of energy with use of the special equipment. For example, generators are intended for transformation of mechanical work into electricity. Other types of energy can be also transformed to mechanical energy. For example, the internal combustion engine in the car will transform chemical energy of fuel to mechanical, used for the movement.