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 effects it and
nothing from inside the system effects anything outside the system. Explain to them that
when people insulate their homes by sealing windows, etc., they are creating an
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 questionsthat 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 lose 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.
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