Teaching About Conservation of Energy

By Kathy Foust

In this lesson plan, use the things students know in life to help them understand what conserving energy really means.

Introducing the Concept

Students learn best via lesson plans based on what they already know in life. Everywhere there are ads and campaigns encouraging people Home 

to conserve energy. But do your students know what it really means to conserve energy? Do they know the laws of science that deal with conserving energy? Give them a leg up on understanding conservation of energy with this lesson plan.

Ask students why their houses are insulated. Let them discuss the idea of conserving energy with you based on the insulation of their homes. Once students have discussed why their homes are insulated, introduce them to the concept of an isolated system. Define an isolated system as a system in which nothing from the outside affects it and nothing from inside the system affects anything outside the system. Explain to them that when people insulate their homes by sealing windows, etc., they are creating an isolated system.

Explain to students that the reason they are trying to create an isolated system is because the Law of Conservation of Total Energy states that the total energy of an isolated system remains constant. Though the energy may change form, it cannot leave the isolated system. Therefore, if their home is an isolated system, no heat can leave it in the winter time and no cooling can leave it in the summer time.

Conservation of Mechanical Energy

Ask your students to consider a falling stone. Assume that the stone has 24 J of energy when it is first dropped. By the time the stone is about to hit the ground, how much energy does the stone have? The answer is 24 J. Students may be confused by this until you fully explain the conservation of mechanical energy to mean that initial energy = final energy. Demonstrate this by explaining the following:

Before the stone is dropped, it had 24 J of potential energy and 0 J of kinetic energy because it isn't moving. As the stone drops, the potential energy is converted into kinetic energy so that by that time the stone is about to hit the ground, it has 0 J of potential energy and 24 J of kinetic energy. No energy is lost, it simply changes form.

Use the conservation of mechanical energy equation to do further demonstrations and walk your students through each step of the formula so they can see how energy is changed instead of lost. If students need further assistance in understanding the Law of Conservation of Energy, refer them to the Law of conservation of Energy Study Guide. Some suggestions for further demonstrations are listed below.

  • Consider a pendulum of a clock. Why does it continue to swing back and forth? Discuss the conservation of energy as it applies to the pendulum being an isolated system and maintaining its own energy. Does the pendulum stop when touched? Once touched, is it an isolated system anymore? These are questions that your students should consider to help them understand the law of conservation of energy as it applies to an isolated system.
  • Create a small greenhouse using a box covered by glass or an empty fish tank if possible. Plant seeds within the greenhouse. As you create the greenhouse, discuss how you have created an isolated system. As the seed grows, discuss how the energy in the greenhouse is conserved through the many changes that take place in the greenhouse. Is energy lost or is it simply changed?

Get creative and create projects to display the law to your students. Even better, ask students to come up with their own isolated system to display their knowledge of the law of conservation of energy.