The law of the conservation of energy states that energy is neither created nor destroyed. Instead, it is simply transferred from one type of energy to another, or from one form of energy to another. The difference between mechanical energy and kinetic energy is that kinetic energy is a type of energy, while mechanical energy is a form of energy.
Work can be defined as the process of energy transfer whereby a force acts upon an object to cause a displacement. If an object is moved, then work has been performed. Work requires three things: a force, a displacement and a cause. For example, if you picked up a book and placed it on the top shelf of a bookshelf, the force would be you lifting the book, the displacement would be the movement of the book and the cause of the movement would be the force you applied.
Types of Energy
There are two types of energy: potential and kinetic. Potential energy is energy that is stored in an object due to its position. This type of energy is not in use but is available to do work. For example, the book possesses potential energy when it is stationary on the top of the bookshelf. Kinetic energy is energy that is possessed by an object due to its motion. For example, if the book were to fall off the shelf, it would possess kinetic energy as it fell. All energy is either potential or kinetic.
Forms of Energy
Mechanical energy is a form of energy. It represents the energy that is possessed by a mechanical system or device due to its motion or position. Stated differently, mechanical energy is the ability of an object to do work. Mechanical energy can be either kinetic (energy in motion) or potential (energy that is stored). The sum of an object's kinetic and potential energy equals the object's total mechanical energy. Other forms of energy include chemical, nuclear, electromagnetic, thermal and sound.
Kinetic vs. Mechanical
The difference between kinetic and mechanical energy is that kinetic is a type of energy, while mechanical is a form that energy takes. For instance, a bow that has been drawn and a bow that is launching an arrow are both examples of mechanical energy. However, they do not both have the same type of energy. The drawn bow is an example of potential energy, because the energy necessary to launch the arrow is only being stored in the bow; while the bow in motion is an example of kinetic energy, because it is doing work. If the arrow strikes a bell, some of its energy will be converted to sound energy. It will no longer be mechanical energy, but it will still be kinetic energy.