(EGY) Law of Conservation of Energy Lesson

Law of Conservation of Energy

The law of conservation of energy states that energy is neither created nor destroyed.  Instead, energy transforms from one form to another. In this lesson, we will be looking at energy transformations.  In other words, we will be looking at the process of changing energy from one form to another.   Let's start by looking at how potential energy converts to kinetic energy and vice versa. Remember, we are not creating any new energy. The total amount of energy in a system stays the same.  

image of coaster car: top of hill: High PE, Low KE end of hill: Low PE, High KE bottom of hill: Minimum PE, Maximum KE As a coaster car loses height, it gains speed; PE is transformed into KE. As a coaster car gains height it loses speed; KE is transformed into PE. The sum of the KE and PE is a constant.

The video below explains the law of conservation of energy. In watching the video, you will see that a good way to think about this law is through visualizing a teeter-totter.  The amount of energy in two interacting systems before they react must be equal to the amount of energy afterward. It must be balanced. Therefore, the total amount of energy does not change. This will also give you a good preview of the different forms of energy that energy can take.

Let's look at two examples:

  • In the swing of a pendulum, you can see potential energy converted to kinetic energy and then back again to potential energy. As you can see in the picture below, the total amount of energy stays the same.  

Pendellum swinging: Potential Energy is greatest at the highest point. Points indicated: PE = 100 J KE = 0 J PE = 30 J KE = 70 J PE = 100 J KE = 0 J PE = 0 J PE=0J KE = 100 J Kinetic Energy is greatest at the lowest point.

  • Another example of potential energy being converted to kinetic energy is a ball falling off of a cliff as seen below:

edge of clitt with the following points indicated: PE = 600 J KE = O J PE = 500 J KE 100 J PE = 400 J KE = 200 J PE = 300 J KE = 300 J PE = 150 J KE = 450 J PE=0J KE = 600 J

Use the activity below to test your knowledge of energy. 

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