Law of Conservation of Energy Study Guide

Page content

What is the Law of Conservation of Energy?

When people say to “conserve energy”, they are generally speaking of not wasting energy or losing energy. The fact is however, that energy cannot be lost, only changed within an isolated system. In general, the isolated system is our atmosphere. Therefore, when energy is said to be “lost” by such things as heat escaping from a home, it is not actually lost. It is still in the atmosphere, though it may have changed

Consider a room full of children. We often say we want them to run around and burn up all their energy. While they may eventually get tired, the energy is still there. It has only changed. The room the children are in is considered an isolated area as long as the door is closed and no one goes in or out of the room. It could be stated that in this situation there is the law of conservation of children since no child is gained or lost.

There are several ways to state the Law of Conservation of Energy. They are listed below.

  • The total energy of an isolated system remains constant.
  • Energy can not be created or destroyed, only changed.
  • In changing from one form to another, energy is always conserved.

Though stated in different ways, these all mean the same thing. Energy may change its form, but it cannot be destroyed and we cannot create it. We can however, manipulate it to change form based on our own needs. For instance, have you ever wondered how a dam works? What we see is trapped water and we know that this is somehow used to create electricity. This is the Law of Conservation of Energy at work. Read the section below to find out how to use the Law of Conservation of Energy Formula.

Law of Conservation of Energy Formula

The Law of Conservation of Energy Formula is as stated below as is concerned with the conservation of mechanical energy.

initial energy = final energy

To use this formula, you must be able to understand and use the formulas for potential and kinetic energies. If you have problems with either of these formulas, see the kinetic energy study guide as well as the potential energy study guide because the above stated formula breaks down as seen below.

(Kinetic energy at time A + Potential energy at time A) = (Kinetic energy at time B + Potential energy at time B)

In other words, if you begin with 13 J of energy, you will end up with 13 J of energy. (J is a representation of joules, the expression of energy units pronounce “jool” and written as “J”.)

How does this help us to understand how such things as a dam work? Consider how high the dam is and where the water comes out. How was this determined. We know it’s not based on looks, but it is based on the amount of energy needed as well as other factors such as what is structurally feasible. Scientists need to decide how much energy they want to convert as well as how much energy they are able to convert. This formula is used to figure out such conversions.