Energy For Free: Perpetual Motion Machines

Author: Mark Roland


1 Class Period

Preparation Time:

10 minutes

Materials: “Drinking Bird” perpetual motion machine

Students will observe the “drinking bird” perpetual motion machine when coming into class. Without the knowledge of how the bird works, it might seem like it will go forever. Of course it will not, and the reasons for this will be discussed. The fallacy of this, and many other perpetual motion machines, will be examined. This serves as an interesting way to reinforce the idea of conservation of energy.

Purpose – The purpose of this lesson is to explore the idea of the conservation of energy. By having the students critically examine the designs of perpetual motion machines, they can see the innate fallacy of such an idea. Of course energy can’t be created!

Students will be able to:
1. Explain the theory of conservation of energy in their own words.
2. Critically analyze machines in order to determine where energy will be lost in the systems surrounding them.

National Science Education Standard:
Content Standard B-Physical Science
The total energy of the universe is constant. Energy can by transferred by collisions in chemical and nuclear reactions, by light waves, other radiations, and in many other ways. However, it can never be destroyed. As these transfers occur, the matter involved becomes steadily less ordered.

Teacher Background

Related and Resource Websites
(Can purchase drinking bird here)



1. As students enter the room, have a “drinking bird” set up as a demonstration. Discuss with the class what they see. Is this machine getting energy for free? Can it run forever? It will only run with the water there, so what is the water’s function? If any students are convinced that it will continue to run indefinitely, allow it to run overnight and see if it is still going the next day.

2. Provide students with the websites (handouts can easily be created from the sites provided, if necessary) containing designs of various perpetual motion machines. Allow the students to examine the drawings and try to find the error in the design.

3. Discuss with the students what they seeing and why. Ask for ideas on why the designs won’t work, and why will the machines eventually stop. Ask students if they have any ideas as to how to keep the drinking bird going indefinitely.

Finish the class by discussing why people continue to look for perpetual motion machines. Basically, you want the students to realize that if one could be built, it could solve the world’s energy problems, but it’s never going to happen. It’s not possible!

Embedded Assessment






PULSE is a project of the Community Outreach and Education Program of the Southwest Environmental Health Sciences Center and is funded by:

NIH/NCRR award #16260-01A1
The Community Outreach and Education Program is part of the Southwest Environmental Health Sciences Center: an NIEHS Award


Supported by NIEHS grant # ES06694

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Last update: November 10, 2009
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