Transference of Energy, by John Cowens
Constructing this simple airplane with your students will demonstrate this basic principle of energy
After years of whining, I finally took the plunge and bought a motorcycle. The following day, I walked out to the garage and put the key in the ignition, put the bike in neutral and squeezed the clutch lever. What an incredible adrenaline rush!
The motorcycle's engine and tires sent vibrations through my body commonly known as transference of energy. An easier way of demonstrating this basic principle of energy is to construct a wooden toy that resembles an airplane without wings or a tail. On the "fuselage," notches are placed from one end to the other. By simply rubbing another stick against the notched square-edge stick, the device produces linear vibrations created by the back-and-forth rubbing motion against the notched surface of the vibrating toy. Energy is quickly transferred through the machine and transformed into elliptical vibrations that cause the false propeller to spin.
When performed properly, students will quickly recognize that stored energy from their body creates the back-and-forth motion of the round stick on the notched surface. Here are the steps on making this fantastic contraption:
Materials (for one contraption):
- one unsharpened wood pencil with graphite center
- one ballpoint pen
- 10 standard flathead thumbtacks
- a plastic pushpin
- scissors
- masking tape
- 1/4" graph paper
- plastic lid (from a margarine tub or coffee can)
- single-hole paper punch
Procedures:
Place the pencil on the desk with the printed lettering facing up. Push the flathead thumbtacks into the pencil. Allow approximately 1/8" of space between the head of each thumbtack.
Wrap masking tape around both the pencil and the thumbtacks to eliminate any sharp metal points from causing injuries. After placing a copious amount of masking tape on the exposed metallic surfaces and the split wood, instruct the students to press the tape down in between the thumbtacks to create notches.
Using the 1/4" graph paper, draw a rectangular propeller blade that is five times longer than it is wide (size ratio – 5:1). In many cases, the students may elect to draw propellers that are 10 blocks long and two blocks wide, and then cut the propeller-blade pattern from the graph paper. They then trace the pattern on the plastic lid and, using the scissors, cut out the traced propeller.
Find the center of the propeller blade by folding the graph paper in half lengthwise and widthwise. Place the pattern on top of the plastic propeller cutout. Use the pushpin to mark the center of the propeller blade. The indentation made by the pin marks the center of the plastic propeller. Enlarge the center opening by using a single-hole paper punch.
Place the pushpin through the center hole of the propeller and push it into the center of the pencil's rubber eraser. Make minor adjustments to be sure the pushpin is not too tight and the propeller is able to spin freely.
Test the contraption independently. Many kids use a ballpoint pen or a pencil to rub back and forth across the notches created by the thumbtacks. If the contraption does not function properly, identify the variables that may cause the problem. The most common problem encountered is not having the plastic propeller properly centered on the pushpin.
Making the propeller spin in one direction:
With your left hand, hold the ballpoint pen and hold the notched pencil in your right hand. Pressure by your thumb on the row of thumbtacks causes the propeller to spin in one direction.
Reversing the propeller's motion:
With your left hand, hold the ballpoint pen and hold the notched pencil in your right hand. Pressure by your index finger on the row of thumbtacks causes the propeller to spin in the opposite direction.
Questions:
What is a machine?
Does this contraption qualify as a machine?
Does the graphite center of the pencil transfer energy better?
John Cowens teaches sixth grade at Fleming Middle School in Grants Pass, OR.
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