Mechanical Energy

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Learning about these two forms of energy is extremely important in understanding why man can obtain the usable energy from things like waterfalls and spinning turbines. Power plants serve to convert these physical forms of energy into energy to run our TVs and cook food in the microwave -- electricity!

Kinetic Energy (KE) is the name for energy associated with moving objects. A good way to remember this is by the formula KE=(1/2)mv2, where m; is the mass of the object and v; is the velocity of the object. If you remember the formula, you will remember that kinetic energy is dependent upon velocity and mass, and thus has to do with moving objects.

Potential Energy (PE) is the name for energy stored in an object--or, the "potential" of an object to do work. For instance, a rock at the top of a cliff has more potential energy than one on the ground, because you could drop the rock off of the cliff and hit something below (converting the potential energy to kinetic).

 

Kinetic Energy

There is an interesting relationship between the final velocity of the object. From Newton's Second Law of Motion,

Also if we set as the final velocity and as the initial velocity there exist a relationship:
Since,
if we apply it to,
the result is,
Here, the quantity is call the kinetic energy, K and is dependent on the velocity and the mass of the moving object.
Since the work done is equal to the final kinetic energy minus the initial kinetic energy, the total work and be described as the change of the object's kinetic energy.

Potential Energy

In most of the cases the change in a form of energy is associated with the tranformation of that energy into another form of energy.
Consider an object of mass m being lifted up a distance h.

The work done by the force applied on the object is equal to mgh. Since motion is in the opposite direction to that of the force of gravity, the work done by gravity in this case is -mgh. The work mgh has been preserved as t he gravitational potential energy, U. In the like manner, the transformation of energy is presented as work.

Therefore,

The Conservation of Mechanical Energy In the previous example, we've seen that the kinetic energy has transformed into potential energy and the work done on the object is the change in energy.


Therefore,

The sum of potential energy and kinetic energy in a system is the total mechanical energy E and it has a constant value.

This is called "The Law of Conservation of Mechanical Energy".
The Law of Conservation of Energy The Law of Conservation of Energy states that energy cannot be neither destroyed nor created and that it is the same in a closed system. Energy that is absorbed into a system must always equal to the energy released.

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