As many of you know, the Learning Cycle is an approach to science instruction developed by Atkin and Karplus in 1962 while working on the SCIS (Science Curriculum Improvement Study) project. 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. The "Learning Cycle" method may be used to teach virtually any topic in physics and that includes Newton's Laws. The forces exploration consists of a "smorgasbord" of twelve activities relating to Newtons laws. This exploratory's emphasis is on the introduction of Newton's 1st, 2nd, and 3rd laws. At each station students are asked to perform one or more activities and answer questions based on their observations. These stations use a variety of manipulatives. Some stations feature common household items; others use either commercial devices or teacher-produced apparatus. I would like to share some of our students' favorite stations with you. During the last 30 years, Dr. James Hicks and I have assembled exploratory activities that we've used to introduce each major topic (for example, forces, energy, optics, wave phenomena, electricity, magnetism, etc.) in our physics classes. These collections contain both time-honored "experiments" and activities that Jim and I have concocted or borrowed from our students or other teachers.
Here are some guidelines for the "Newton Adventure":
- An exploratory is a collection of introductory science activities that relate to a single topic or concept. Exploratories provide students with a common experiential base while igniting their interest.
- The activities are arranged as numbered stations around the room. Manipulatives at each station provide opportunities for exploration and discovery.
- The exploratory uses a guided inquiry approach. The guidance is provided through instructions and questions that accompany each station. The teacher remains in the background and assists only when asked.
- The activities may be done in any order.
- A non-judgmental approach is used. At this point, the teacher should be focusing on the quality of a student's reasoning, not whether an answer is right or wrong. The teacher is given an opportunity to listen to students dialog with peers and formulate explanations. Student pre-conceptions are revealed during this phase of the learning cycle.
- Exploratories encourage student engagement. Intriguing manipulatives tend to get even the most disinterested students involved. Since discrepant events leave the students with a need to know, the class discussion that follows an exploratory is teacher led, but student-driven.
- Exploratories provide qualitative experiences. Quantitative laboratory work is done later.
- Placing instructions at each station eliminates duplicating costs. Laminating the instructions allows them to be reused.
Newton's First Law (a.k.a., Galileo's Law of Inertia.)
Station 1: Not with my dishes, you don't!
Haven't you always wanted to try the old table cloth and dishes trick? To perform this time-honored magician's trick, place some old dishes (you may want to begin with a single plate) on a smooth tablecloth. Grab both ends of the tablecloth and, without hesitation, pull the tablecloth out from under the dishes as quickly as you can.
- Was it magic or physics? In other words, why did the dishes remain virtually motionless when the tablecloth was quickly pulled out from under them?
- Did the dishes move at all? Why?
- Why was a smooth tablecloth used? What do you think would happen if a rough material, e.g. sandpaper, were used?
Station 2: Tee-off Time
Balance an embroidery hoop on the mouth of an empty flask or glass soda or catsup bottle (see photo). Now place an inverted golf tee on the top of the hoop. Note: a piece of chalk with a flat bottom also works well. Make certain that the tee is directly over the mouth of the bottle. Now take a deep breath, and remove the hoop by quickly grabbing the inside center of the hoop.
- What happened to the tee?
- Why did the tee drop into the container?
- Repeat the experiment, this time quickly grab the outside of the hoop. What happens now? Can you explain your observation? That is, why does the tee only fall straight down when the hoop is grabbed on the inside?
Station 3: Looking Back
Bend a stiff piece of wire, such as a coat hanger, into the shape shown in the figure. Using two sticks of modeling clay, fashion two spheres of clay around each end of the wire. Balance the center point of the wire on the top of your head. Make certain that the wireframe does not come in contact with your ears. Now quickly spin around.
- Describe the motion of the frame and spheres as your body spins around.
- Can you explain why the apparatus on your head barely budges as you move?
Station 4: Egg Pizza
Fill a medium sized beaker, wide-mouth glass, or coffee cup 1/2 full with water. Place the container, a pizza pan, a cardboard cylinder fashioned from a file card, and a hard-boiled egg near the edge of a table as is shown in the figure. The egg and cylinder must be directly over the beaker. Also, the pizza pan must extend beyond the edge of the table. Believe it or not, the object of this activity is to knock the pizza pan and cardboard cylinder out from under the egg so that the egg will fall straight down into the beaker!
To accomplish this feat, a broom will be used as a pizza pan "launcher." Place the broom handle next to the edge of the pizza pan. With your foot on the bristles of the broom, "cock" the broom by pulling the handle away from the pan. This will put the handle under tension. Now, without hesitation, release the handle. With luck, the egg should drop into the beaker. For a greater challenge, increase the number of eggs, beakers, etc.
- Why did the egg fall straight down and not move with the cardboard cylinder and pizza pan?
- Do you think the mass of the object placed on the cylinder matters? Please explain your reasoning. You may wish to check your answer by replacing the egg with a ping pong ball.
Station 5: Egg Spin
In this "eggsperiment" you will use two eggs, one marked with an "O", the other with an "X." Spin the egg marked with an "X." Now stop the egg with your hand. Immediately after the egg stops, remove your hand. Describe what happens. Now spin the egg marked with an "O." Again stop the egg with your hand and then quickly release it. Describes what happens this time.
(Teacher's note: One egg is raw and the other is hardboiled)
- Why do think the two eggs behave the way they do?
- How could a cook make practical use of the results of this experiment?
Station 6: Revolution
Give the Revolution a gentle spin and watch it continue spinning in a state of near perpetual motion. Amazing!
- Does the spinning axle eventually come to rest? Why?
- If all frictional forces could be eliminated, how long do you think the axle would spin?
Newton's Second Law
Station 7: Jelly Jar Accelerometer
An accelerometer is a device that may be used to determine the direction of an object's acceleration. An accelerometer also gives the direction of any unbalanced force acting on an object. There are many types of accelerometers. One of the simplest is made out of a jar, a bobber and some string.
To construct an accelerometer, glue a string to the inside center of the lid of a jelly or peanut butter jar. The length of the string should be slightly less than the height of the jar. For reasons of safety, a plastic jar is always preferable. Attach a plastic bobber to the free end of string. After filling the jar with water, with the bobber and string on the surface of the water, place the lid on the jar. Now tighten the lid and invert the jar. The bobber should now be located just below the glass bottom of the jar. If it's dragging on the glass bottom, remove the lid and slide the bobber along the string so that it is closer to the lid. You are now ready to use your accelerometer.
- Hold the accelerometer in your hand. Which way does the bobber point when you are standing still?
- Which way does the bobber point as you walk at a smooth, constant rate?
- Watch the bobber as you start from rest and accelerate to the right. Which way did it point as you picked up speed? As you slowed down to a stop? You may have to repeat this part of the experiment several times in order to see all that's going on.
- Repeat part (iii), this time accelerating to the left.
- How does the direction of the unbalanced force you are exerting on the accelerometer with your hand compare to the direction of acceleration?
- Holding the accelerometer in front of you at arm's length, spin in a circle. (Be careful not to get too dizzy!) Observe the direction in which the bobber is pointing. According to the accelerometer, what is the direction of the jar's acceleration? In which direction are you exerting an unbalanced force on the jar?
Newton's Third Law
Station 8: That's Repulsive!
Obtain two small magnets. Can you make the two magnets attract each other? Repel each other? Place the two magnets on the table and align them so that they repel each other. Bring them close together and then release them.
- Describe what you observe.
- Does each magnet exert a push on the other magnet?
- How do you know?
- Compare the strength of the two forces.
Station 9: So Attractive?
Arrange two small magnets so that they attract each other. Separate the magnets so they are one or two centimeters apart and then release them.
- Describe what you observe.
- Does each magnet exert a pull on the other magnet? How do you know?
- Compare the strength of the two forces.
Station 10: Tug of War!
Using two spring scales, have a tame "tug of war" with your partner. Observe the readings on the two scales during the tug of war (don't pull too hard!).Questions:
- Describe the readings on the scales.
- Can you and your partner pull in a way that will produce a higher reading on one scale than the other?
- Can you and your partner pull in a way that will produce a reading of zero on one scale but not on the other?
- Explain your answer.
Station 11: The Big Push
With your lab partner, hold two Newton Scales back to back. Now push on the scales and observe both readings.
- How do the readings compare?
- Can you and your partner push in a way that will produce a higher reading on one scale than the other?
- Summarize your findings from stations 10 and 11.
Station 12: Up Up and Away!
The Balloon Helicopter is a toy Newton would have loved! Blow up the balloon and attach the hub to the blade assembly. Now release the helicopter and watch it go!
- Why do you think the helicopter flies?
- Do the helicopter's blades push on the surrounding air? How do you know this?
- Does the air surrounding the blades push on the blades?
- Which of these two forces causes the helicopter's motion?
- Would a helicopter fly in outer space where there is no atmosphere?
The students have completed the exploratory. What's next? During the next segment of the learning cycle, the concept development phase, 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 laboratory activity. The wonderful news is that students do not have to be coaxed into participating. The exploratory almost always leaves kids with unanswered questions. This produces what Piaget referred to as disequilibrium. In this state, students have a need to know and are motivated to ask questions. This phase is particularly exciting because the teacher and students are given an opportunity to listen to each other's explanations. With the guidance of the teacher, meaning and understanding begin to emerge from conflicting ideas.
In addition to discussion, a variety of methodologies may be employed during this concept development stage of the learning cycle. They include reading, computer work, or demonstrations. At this time, it may even be appropriate for the students to return to the laboratory to test a hypothesis that was brought up during class discussion.
During the last phase of the learning cycle, students return to the laboratory where they engage in real-life applications of their newly acquired knowledge. These activities may be done in a conventional laboratory or in some rather unorthodox settings. Regardless of the venue, students apply the physics they have just learned in a meaningful and quantitative way.
For the last 25 years we've had students push cars with bathroom scales in the school's parking lot as an application of Newton's Second Law of Motion. The bathroom scales provide a known force and regularly dropped safety cones are used to obtain the vehicle's acceleration. We use the acceleration and force to calculate the vehicle's mass. While this may seem a little strange, it illustrates to students that the material studied in class pertains to objects both small and large. Of course students always want to push things to the limit and this annual event is certainly no exception.
Each year I ask students to bring in their own cars for the lab. I usually get cars ranging from a sub compact to a SUV. A few years ago a student said he could arrange for a couple of vehicles that might be interesting to use, but he wasn't saying what he had in mind. When my class convened in the parking lot the next day, there sat a school bus and a Hummer ready to be pushed. Mind you, this was when the Hummer had just become commercially available. Not only did my students go wild, but there were cheering students, teachers and administrators leaning out of every single window of our four-story school.
As my students pushed the two "monsters of the midway" and a variety of other cars and trucks, hundreds of witnesses saw Newton come through one more time. It might be said that conventional learning went out the window for a while that day, but the force was certainly with real-life physics!