The Law of Conservation of Energy

Energy is found everywhere in our universe, we use mechanical energy to do mechanical work every day. All the types of energy in our universe involve kinetic energy, potential energy or both. Some examples of energy are radiant energy, electrical energy, thermal energy, sound energy, etc (Fig. 1). Some many be worried that one day there will be no more energy in the universe, but it is proven that we will never run out of energy, in the sense that the energy we use will not be destroyed or created, this is called The Law of Conservation of Energy.

Fig. 1 There are many different types of energy, we experience many of these types in our every day lives. Credit:

What is The Law of Conservation of Energy?

This law is defined as the “energy that is neither created nor destroyed; when energy is transformed from one form into another, no energy is lost.” 

The total amount of energy in the universe never disappears, while new energy cannot be created out of nothing. The energy that is present can only be changed from one form to another. When this energy transformation happens no energy is lost, one form of energy is reduced by the same amount that the quantity of the other form/forms is increased, meaning that the total amount of energy stays constant.

For example, a light bulb (Fig.2) turns 100 J of electrical energy into 5 J of radiant energy and 95 J of thermal energy (side note: which is not very efficient!). This shows that no energy has been lost because 95 J + 5 J = 100 J. ( Nelson Physics 11 p. 237)

Fig. 2 The inefficient incandescent light bulb. Credits:

Not only is understanding The Law of Conservation of Energy very important, we must understand the factors in dealing with this law, that is potential and kinetic energy.

Potential energy is a form of energy an object possesses and this can be described as “stored” energy.

Kinetic energy is the form of energy an object possesses due to motion.

Watch this video to understand how kinetic energy and potential energy works with the law. 

Once you have understood the law and how it relates to potential and kinetic energy, you have the ability to use the formula:

Em = Eg + Ek  ( total mechanical energy = potential energy + kinetic energy) 

This formula will help you solve problems that relate to the law of conservation of energy by finding the total mechanical energy at one point in motion of the object and relating it to the total mechanical energy at another point.


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