Introducing Energy with the Learning CycleArbor Scientific
Learning Cycle is an approach to science instruction developed by Atkin and Karplus in 1962.
This approach puts the phenomena first. Names and numbers are brought into the picture only after students are allowed direct contact with the phenomena. Although there are a number of variations on the theme, the essential learning cycle consists of three phases. These phases include exploration, concept development and application. In this issue I would like to cover some of the aspects of the Concept Development stage.
During concept development, basic principles emerge, terminology is introduced, and mathematical relationships are derived. With the teacher serving as a guide, students construct meaning from observations made during the exploratory. How is this accomplished?
I generally engage students in class discussion immediately after their exploratory activities. At this point, students have a need to know and are motivated to talk about what they have just encountered in the lab. This discussion is most effective when it is student-centered with the teacher serving as a facilitator, not as a dispenser of knowledge. The goal of the process is to have meaning and understanding emerge from conflicting ideas about the phenomena.
While it is desirable for students to drive the discussion regarding the phenomena encountered during the exploration, it is the teacher who must develop a mechanism for introducing terminology and mathematical relationships. Sometimes another activity is the answer. The written instructions for the activity can introduce students to formulae and terminology as well as provide them with instructions for carrying out the experiment. Such a lab may be used to acquaint students with the needed terms and equations in a very natural and engaging way. A subsequent discussion, video and worksheet may then be used to conclude the concept development phase.
An activity from my energy learning cycle illustrates this approach. I use the time-honored “student power lab” because it presents terms and concepts in a meaningful context. The lab sheet not only provides students with instructions for carrying out the experiment, but also introduces them to the vocabulary, formulae and units relating to work, power and energy. In the experiment students determine the power they develop running or walking up stairs. They calculate the work they do by multiplying their weight by the vertical distance traversed. Dividing the work by the time of ascent yields power. The goal: students assimilate key concepts by using them.
Of course a variety of methodologies may be employed during the concept development stage of the learning cycle. They include reading, computer work, video clips or demonstrations.
The following quote from physics teacher Tom Kozikowski provides an example of a highly effective approach to bridging the exploratory and concept development phases of the cycle. The first two portions of the learning cycle were terrific. The students were engaged and really thinking deeply about the physics concepts. As a homework assignment after the exploration, before we had any class discussion or any readings on Newton’s Laws, I asked the students to state each of Newton’s Laws in their own words and then to support their statement with evidence from the activities. Although few students stated the Laws as soundly as Newton himself, I was very proud of the conclusions they developed and the support they provided. The students and I have found this learning cycle to be excellent!!!
Energy Learning Cycle Exploratory
Station1 Hot Stuff Burning any type of food never ceases to amaze students. They have always heard that the food we eat provides our bodies with energy, but they never think that the energy stored in a single sugar cube could be transformed into so much heat and light. We’ve had kids burn everything from peanuts to dried out jelly doughnuts.
a) Place a piece of food on the tip of a dissecting needle or in a paper clip. Now light the food on fire. Measure the time it takes for the food to burn.
b) What type of energy does burning food produce? What is the source of this energy?
c) Select two different food samples of comparable size. Which do you think will burn longer? Burn the two samples separately and compare the length of the burn. What did you observe about the energy content of the two samples?
Student shown here burning a potato chip using a home-made calorimeter.
a) Compress one of the “poppers”. Do you do work compressing the elastic material?
b) What becomes of the work you did?
c) Describe the energy transformation(s) that occur when the toy jumps.
d) What becomes of the popper’s energy once it has come to rest on the table?
Station 2 Potent Poppers!
An inexpensive toy, called the popper allows students to investigate a variety of energy transformations. Initially work is done in deforming the popper. When the popper abruptly returns to its original shape, its elastic potential energy is transformed into kinetic energy and then gravitational potential energy and then back into kinetic energy.
The popper may also be used to demonstrate activation energy. Note that when dropped from a low height, a small amount of activation energy results in the release of considerably more energy.
Enter another station and image the amazing smashing steel spheres! These 2-inch, 1 pound ball bearings clearly demonstrate the eventual fate of most forms of energy. Smelling a piece of paper placed between colliding spheres reveals that the kinetic energy possessed by the moving spheres has been converted into heat. A rather impressive variation on this experiment can be done with the Newtonian Demonstrator, if you happen to have one. Try it with a small piece of flash paper!
a) Place a piece of paper between the two spheres. Now smash them together. After the spheres collide, smell the area on the paper where they came into contact. What do you detect? What do you suppose caused this odor?
b) Did the paper get hot? That is, where did the energy come from that was responsible for the heating? As best you can, describe the energy transformation that took place as a result of the collision.
b) Examine the point of contact. Do you observe any signs of scorching on the paper? What can you conclude about the increase in the paper’s temperature? In theory, what could you do to cause combustion?
The Forever Flashlight
Station 4 Crank it Up…
The Don Rathjen’s “Forever Flashlight” (drawing below) permits students to see how mechanical energy may be transformed first into electrical energy and then into light. Five disk magnets sliding through a coil of wire light an LED coming and going.
a) While holding the Forever Flashlight in your hand, note the LED. Now shake it so that the magnets slide back and forth through the tube. What did you observe?
b) Purpose an explanation for your observation?
c) What energy transformations does this device illustrate?
Station 5 More Power! er er er..
This station can actually be broken up into a number of events based on your resources. The Genecon hand-operated generator takes this concept one step further. It is versatile, easy to use, and provides students with a kinesthetic learning experience. Mechanical energy may be transformed into a variety of forms. These include heat, light, sound, motion and electrical potential energy. We use old miniature Christmas tree lights, transistor radios, one-Farad capacitors, and a liquid crystal thermometer attached to a 5-ohm power resistor and the toy train you see on the right.
Students love to connect two generators together. They learn about the motor-generator principle without being told. Paraphrasing Eric Rodgers: “you can’t tell which is agent and which is victim.” By counting the number of turns of the motor unit produced by 10 turns of the generator, it is possible to determine the efficiency of the generator-motor system.
a) Obtain a Genecon hand-cranked generator. To see if yours is functioning properly, you may check it by connecting the two clips attached to the Genecon’s leads to a small light bulb. What happens when you turn the crank clockwise? What happens when you turn the crank in the opposite direction?
b) Adjust the rate at which you turn the crank. What happens when the crank is turned rapidly? turned slowly?
c) Describe the energy changes taking place when you light the bulb.
d) Connect your generator to the resistor/heat sensor device. Turn the crank rapidly for a fairly long time and watch the thermometer strip. What happens? Describe all the energy changes taking place.
e) Connect your generator to a capacitor. Turn the crank for a minute or two and then let go of the generator handle. What happens?
f) Recharge the capacitor and quickly disconnect it from the generator. Now connect the leads to one of the light bulbs. What do you observe? Discuss the energy transformations taking place.
g) Connect your generator to another generator and turn the crank. What do you see? Describe the energy changes that are taking place.
Now line the two generators up with both of their handles pointing straight up. Turn the generator ten times while your partner counts the number of turns made by the Genecon that is serving as a motor. Calculate the efficiency of the two Genecon system. (Note: the efficiency of the generators is equal to the number of turns of the motor divided by the number of turns of the hand-cranked generator.)
Teacher’s Note: Sweaty hands will increase the meter reading. You might have a student exercise first then check the reading.
Station 6 The Human Touch
The hand battery uses copper and aluminum plates connected to a galvanometer. An electric current is produced by placing your hands on the plates.
a) Examine the “Hand Battery.” Describe the construction of this device as best you can. Use a sketch if necessary.
b) Observe the meter while you place your hand on the adjacent copper and aluminum plates. What did you observe? How do you suppose this device works?
c) Try pressing down harder on the plates. Did this alter the meter reading? Why? What energy transformations do you suppose is taking place?
d) Compare your meter reading, with a friend
Station 7 You Light up my Life
You have no doubt seen the Radiometer many times. However students always seem to find the concepts of this simple device fascinating as well as baffling.
a) Examine the radiometer (glass bulb with four rotating vanes.) Now bring a light bulb close to the Radiometer (approx. 10cm.). What did you observe?
b) Examine the radiometer closely. What is the direction of movement? Which colored side of the vanes leads?
c) Can you explain the operation of the Radiometer based on the direction of rotation of the vanes?
d) Predict what would happen if the light source was moved closer or farther away? Test your predictions.
The Rubber Band Machine
From the Singapore Science Center Energy Exhibit
Station 8 The Heat is On!
Natural rubber is a substance which can stretch many times its original length. During extension, rubber gives off heat and as it contracts it absorbs heat. In addition, when a stretched rubber is heated, it contracts. This property of rubber is used in the rubber band machine on the left. The infra-red lamp heats up the rubber bands nearest to it, causing them to contract. The contraction causes the center of gravity of the wheel to shift towards the lamp, and the wheel becomes unbalanced and turns.
Use a large size rubber band for this next station, a smaller one might break and snap the “Cheek’ee” in the face!
a) Pull or stretch a rubber band or balloon as you hold it up to your cheek. Describe how it feels.
b) While holding it to your cheek, allow it to contract quickly. How does the rubber band feel now?
Station 9 Getting Juice from Juice
Using a knife, make two small slits in the surface of a lemon, potato or apple. You can use metal strips or coins, key is to use dissimilar metals. After cleaning the outer surfaces of a dime and penny (or metal strips) with sandpaper, insert the coins in the slits. Note: a short length of copper pipe (any diameter) and a galvanized nail also work well.
a) What happens when the galvanometer leads are touched to the outer edges of the coins or pieces of metal?
b) Increase, and then decrease, the depth to which the coins (or metal) are inserted into the fruit. Do you detect any change in the galvanometer reading as you make these changes? Why do you suppose this happens?
c) You can increase the voltage produced by this simple electrical device by connecting a number of the lemon cells together in series. This means that you connect a penny in one cell to a dime in another cell until all cells are connected. When you finish making these links, connect the coins at each end of the chain (a penny at one end and a dime at the other) to the galvanometer. What happens? Try using four or five cells in series to light a small light bulb or red LED (light emitting diode).
Station 10 Basking in the After Glow
The main component of this station is a large piece of pink insulation foam covered with a sheet of phosphorescent material. The station can be set up two different ways. In the first version the screen is placed in a totally dark area. A person is directed to stand close to the phosphorescent screen, select a pose, and have a partner trigger an electronic flash unit. When the person moves away from the screen, the area touched by the light of the flash glows an eerie green. An Image of the person remains on the screen as a shadow. The shadow lingers on the screen for several moments. Another way to use this idea is to illuminate the phosphorescent screen with a black light causing the whole screen to glow. A person stands near the screen blocking out the black light and casting a shadow on the screen. When the person moves, his image remains on the screen. The shadow does not last as long as in the first version, but this set-up eliminates the need for complete darkness and an electronic flash.
a) Energize the phosphorescent screen with a bright light source. What happens when the light is taken away?
b) Suggest a mechanism that would explain the screen’s ability to glow after exposure to light.
c) Place your hand on the screen and once again illuminate with bright light. Describe what happens after removing your hand and the light.
d) Explain your observations.
e) Does the length of exposure have any bearing on the glow?
f) Try different color lights, does this have any effect on the glow? Can you explain your observations?
During the last phase of the learning cycle, students apply the ideas developed during the concept development phase of the cycle. Returning to the laboratory, they perform an experiment that requires them to compute the potential and kinetic energies of an object as it moves along a track. One method involves strobe photography (see Heath Physics). A strobe photo is made of a toy car as it moves down a Hot Wheels track. Analysis of the photo provides information that may be used to compute the car’s potential and kinetic energy at each point along the track. An alternate approach uses apparatus such as a low-friction track, a photo gate and electronic timer. (see below)
In either case, the students discover that the total mechanical energy is, for all practical purposes, conserved! As the above student-produced graph indicates, the total mechanical energy of the system remains virtually constant throughout the motion.
As a second application activity, our students take an excursion to Six Flags Great America. There they experience the laws of physics operating on a grand scale. In particular, they view roller coasters in a new light. They now see them as energy transformation machines. Using triangulation, students measure the height of the roller coasters. From this information they can compute the coasters’ potential energy. Using the law of conservation of energy, they proceed to determine the theoretical speed at various points along the ride. Measuring the speed of the coaster, using distance over time techniques, students estimate the frictional loses incurred during the coaster’s trip by comparing gravitational potential energy at the beginning of the ride with the kinetic energy near the end.
We have found the learning cycle approach to teaching energy concepts to be very effective for a number of reasons:
1) Energy is a difficult concept. With the learning cycle, students are provided the opportunity to deal with objects on a concrete level before formal concepts are introduced. This is in accordance with the precepts of Piaget and current cognitive research.
2) The learning cycle makes energy meaningful. Students are made aware of the importance of the energy transformations that are continually going on all around them. Applications of material being studied are intrinsic to the cycle.
3) This student-centered approach encourages student engagement. Intriguing manipulatives tend to get the most disinterested students involved. Discrepant events leave students with a need to know.
4) The energy learning cycle provides a variety of kinesthetic learning experiences. While turning the crank of a Genecon, students really understand what is meant by “you can’t something for nothing.”
5) Using the learning cycle, you have an opportunity to listen to the students dialog with peers and formulate explanations. For me, this has always been one of the most exciting aspects of teaching.