This a summary of a workshop presented at the ICPE-GIREP International Conference Hands-on Experiments in Physics Education in Duisburg, Germany, August 28, 1998.
PHYSICS AND TOYS - PHYSICS FUN FOR EVERYONE
Raymond C. Turner, Department of Physics and Astronomy, Clemson University, Clemson, South Carolina 29634-1911 (USA)
Beverley A. P. Taylor, Department of Physics, Miami University, 1601 Peck Boulevard, Hamilton, Ohio 45011, (USA)
Physics is an exciting science and it can be made fun through the use of ordinary children's toys. This hands-on workshop was designed for teachers at all levels in search of fun physics demonstrations, lab experiments, and interactive materials for their students. More than 50 toys were demonstrated, and the physical principles related to these toys discussed. Everyone had the opportunity to participate in both qualitative and quantitative investigations using the toys. The workshop leaders have found that toys can be utilized at all grade levels from kindergarten through college by varying the sophistication of the analysis. The aim of the workshop was to provide participants with information that would assist them in developing toy-based lessons and finding demonstrations of physical principles for their students.
In this paper we describe many of the toys which were demonstrated, and give indications of the physical principles which might be discussed using these toys. More detailed discussion is given for only a small number of the toys.
Section 1. Whistling Balloon Helicopter
A picture of the Whistling Balloon Helicopter is shown in Figure 1. To operate the toy, you first inflate the balloon, then attach it to the helicopter blades, and finally release the toy. The helicopter blades will rotate, causing the helicopter to rise into the air, while emitting a loud whistle.
The workshop participants first tried the toy and then were then asked to cite some physical principles that were related to the toy's operation. Examples given included Newton's Second and Third Laws, kinetic and potential energies, angular momentum and torque, pressure, and Bernoulli's principle. While we stopped the discussion after about 15 different physical concepts were given, more than 30 can easily be listed. For a toy that costs less than US $1, there is probably more physics for your money here than in any other device that we have.
Several balancing toys are shown in Figure 2. These include a Weeble® (Weebles wobble but they don't fall down), Minnie Mouse®, a balancing bird, and Ernest® the balancing bear. (1) The toys can be used to discuss equilibrium, center of mass, and torque among other things. Minnie and the Weeble obviously contain a weight in the bottom, so that when they are tipped, the weight is raised and the gravitational force (torque) causes them to return to the upright position. The behavior of the balancing bird is not quite as obvious. In this case, it is the weight concentrated in the wing tips that causes its center of mass to be below its balance point, resulting in stable equilibrium. Ernest doesn't balance at all when he is as shown in the figure. But when rods with weights on them are inserted in the handlebars of his bike, he balances very well, and can ride his unicycle along a string stretched across the room.
In Figure 3 are shown several bouncing toys which demonstrate a variety of physical phenomena. The High Bounce/No Bounce Balls (happy/sad balls) are neoprene rubber balls which feel very much the same when squeezed, but behave very differently when bounced. One ball bounces quite high (like a super ball) while the other doesn't bounce at all (like a ball of clay). These balls can be used to discuss the properties of materials as well as to discuss different types of collisions. Super balls can be used to discuss the energy lost when they are dropped and allowed to bounce, and this discussion can be extended by dropping them onto a variety of different surfaces. A Hopper-Popper® is a toy that is similar to about one-third of a hollow rubber ball. When this is turned inside out, and dropped from a height of about one meter, it will "bounce" to a height of about one and one-half meters. This certainly attracts the students' attention, and can then be used to discuss conservation of energy and the different types of mechanical energy. The Krazy Roll-A-Ball® has an off-center weight embedded in it, so that its rotational motion is not about the geometrical center of the ball. When it is tossed into the air with a rotational motion, it appears to wobble in a crazy way (but it is just rotating about its center of mass). Also, when it is rolled along a table, its motion is very erratic as its center of mass changes its position up-or-down, or sideways.
Several toys, which use springs or rubber bands to store energy, are shown in Figure 4. These toys can generate lively discussions about potential energy and energy transformations. The pumpkin spring-up and Mother-N-Baby are nice examples of work being done (a force clearly moves), energy being stored as elastic potential energy, then later being changed into kinetic energy. The Eggscaper and crazy wheel, both of which are wind-up toys, as well as the flip frog, also lend themselves to the discussion of other physics concepts. The egg of the Eggscaper explodes to reveal the hopping chick conserving linear momentum in the process. The crazy wheel has an off-center weight in it, so it moves in unexpected ways. The flip frog is an excellent example of Newton's third law. A spring pulls up on the back of its feet, forcing its toes down against the table and it flips over backwards. Further information about these toys can be found in "Exploring Energy with Toys: Complete Lessons for Grades 4-8." (2)
Three additional energy transformation toys are shown in Figure 5. The Shuttle-Go-Round runs on batteries; therefore, chemical and electrical energy can be introduced into the discussion. Toys that roll back to you have been common folk toys over the years, but the Car Come-Back takes the common toy to another level. Not only does it come back to you, but it actually turns around in the process. Figuring out the mechanism which causes it to turn can be a good learning experience for students. Often in discussing the energy transformations which occur when a ball bounces, one tells students to think of a ball as being made of tiny springs. The Ka-bong Ball is a nice visual aid in that it really is made out of springs.
A variety of toys can be used to illustrate different aspects of pressure. Shown in Figure 6 are a popgun, a dart gun, the Mystery Blow Pipe, and The Hang Up. The popgun is a hollow rubber gun with a ping-pong ball inserted in the end. When the gun is squeezed, its volume decreases, its pressure increases, and the ball shoots out. The dart gun shoots a soft rubber dart which will stick to a smooth surface. This behavior can then be used to discuss atmospheric pressure. In addition, the dart gun can be used to discuss projectile motion, both with and without air resistance. The ball in the Mystery Blow Pipe will rise up when air is blown into the pipe, and it will remain over the pipe as the pipe is moved. The ball's reasonably stable position can be understood by applying Bernoulli's Principle. The Hang Up is a similar toy which has the added challenge of hooking the ball in the loop.
The toys in Figure 7 include a tiger Cartesian diver, a Happy Bird, and a Magic Love Meter. (3) The tiger will float in the bottle of water until the bottle is squeezed, increasing the pressure. Additional water then enters a small hole in the tiger, and it sinks due to its increased density. When the head of the Happy Bird is moistened with water, the bird will repeatedly tip over and appear to be drinking from a cup placed in front of it. This operation is due to the evaporating water which cools the bird's head, reducing the pressure of the gas inside, so that the liquid inside the bird rises, causing it to tip and appear to be drinking. The Magic Love Meter is a hand boiler. When the gas in the lower portion of the glass bulb is warmed by holding it in your hand, the liquid rises into the upper glass ball and the vapor bubbles vigorously through the liquid so that it appears to be boiling.
The balloon racer, water rocket, and Rat Fink Hydro Racer shown in Figure 8 can all be used to discuss conservation of momentum. The Hydro Racer is basically a horizontal water rocket. Water is pumped into a thick rubber balloon, then allowed to rapidly squirt out when the toy is released from the pump. The bendable bunny and building blocks in the same figure can be used to illustrate finding the center of mass of an object. The center of mass of the bunny can be estimated by dangling it from one arm then the other. If you then change the position of the legs and repeat the process, the center of mass has clearly changed. The building blocks are called Radical Blocks and can be used to build things that seem impossible because their center of mass does not appear to be over the base of support. The catch is that some of the blocks are solid, others are hollow, and still others have off-center weights; thus, the center of mass is not where a simple estimation puts it.
A variety of circular motion toys are shown in Figure 9. The Christmas tree spinner, humdinger, and ribbon spinner all show things moving outward when there is insufficient centripetal force to cause them to move in a circle at their initial radius. The humdinger is the less familiar of the group and is essentially a button-on-a-string folk toy with the button being made from a stretchy polymer material. To get the ball in the cup one must cause the ball to move initially in a circular motion then switch over to parabolic free-fall at just the right moment. When the bungee jumper is spun in a vertical circle, the spring is stretched more at the bottom than at the top showing that the force is larger at the bottom.
The talking cup, squawking chicken, and train whistle shown in Figure 10 all produce sound. The cup says Merry Christmas when one runs a thumb down the ridged plastic ribbon. This can be done with the ribbon in and out of the cup to show the how the cup acts to make the sound louder. The squawking chicken is a homemade version of the same toy made from a plastic drinking cup and string. When the string is tugged with a damp cloth or sponge, a squawking noise is heard. The train whistle, which is easily cut open, contains four resonant tubes with lengths differing by about two centimeters.
Also in Figure 10 are three toys relating to light. The rainbow glasses have tri-sectioned eyepieces which can be rotated so one can look through each section in turn. Each section is a different color filter (red, green and yellow), so one can talk about the effect of the filter on the light passing through it. The reflect-a-sketch uses a piece of Plexiglas as a half-reflecting mirror. The mirror-reversed pictures, which come with the toy, can be seen reflected in the mirror and traced. The Jumping Colors set contains six colored markers that can be used to make drawings that appear to be three-dimensional when viewed with the enclosed diffraction grating glasses.
More light toys are shown in Figure 11. The periscope uses two mirrors in the observation of an object, and it can be used to begin a discussion of ray tracing. The mirrors in this toy can also be rotated so that the students can look at objects behind them. The image in this case is inverted which allows for more discussion and analysis. (4) In the Art Bank, a small box appears to float in the bank, while deposited coins disappear. In the Star Wars box, an image of Darth Vader is seen from one angle, while Yoda is seen from a slightly different angle. Both toys use a flat mirror to provide these illusions. The Fiber Flashlight has plastic fibers that channel colored light along the fibers. This toy can be used to introduce the concepts of both fiber optics and total internal reflection.
Two toys based on electrostatic forces are included in Figure 12 along with one magnetic toy and one that uses current electricity. The Static Stick is a very simple toy in which the outside of a plastic tube is rubbed to create forces on bits of Styrofoam inside the tube. Using the charged Mystic wand one can levitate a charged ring or other shape made from thin Styrofoam. By measuring the mass of the ring and estimating the average distance between the ring and wand, one can calculate an approximate charge for the ring and wand. (5) Depending on the mathematical sophistication of the class, one could approximate the ring and wand as two point charges, as a line of charge and a point charge, or as a line and a ring of charge.
The goal of the Tri-Zany game is to balance six magnetic marbles on pedestals. This is more complicated than it sounds due to the interacting magnetic fields of the marbles. The last toy in Figure 12 is a flashlight that contains a simple electric generator. The hand crank spins a magnet over a loop of wire that is connected to the light bulb. The flashlight can be easily opened up to show how the various parts work together to create the current.
Some additional magnetic toys are shown in Figure 13. The Whee-Lo consists of a metal track and a magnetic wheel which sticks to the track as the wheel rolls back and forth both over and under the track. The Snake and Top is a small metal snake which slithers back and forth when it touches the magnetic tip of the rotating top. Robby the magnetic seal and ball is an ingenious arrangement of magnets in the seal and in the ball which causes the ball to rotate as the seal is brought near to it. The magnet in the seal is oriented so that it exerts both a torque and a repulsive force on the ball. This causes the ball to tip slightly and then rotate. The rotation continues as long as the seal is moved toward the ball. (6)
A Wild Flicker Light and a Space Wheel are shown in Figure 14. The Flicker Light has a long filament which carries an alternating current when it is plugged into an AC source. A magnet near the top of the bulb causes the filament to vibrate, demonstrating the magnetic force on a current carrying wire. When the magnetic force is large enough, the filament vibrates in a crazy fashion, apparently demonstrating chaotic motion, so this novel lamp can be used to introduce the concept of chaos. The Space Wheel is a toy which rolls back and forth forever (or until the battery wears out). While it is not an example of perpetual motion as some students might believe, it is an excellent demonstration of the laws of electromagnetism (Faraday's Law, Lenz's Law, and Ampere's Law). The rotating wheel contains a magnet that induces a voltage in a coil in the base of the toy which turns on a circuit containing a battery and a second coil. The induced voltage in the first coil opposes the motion of the rolling magnet. The second coil is wound in the opposite direction from the first, so that the current in it produces a magnetic field that aids the motion of the wheel, and keeps it moving almost indefinitely. (4)
A variety of toys have been found to be suitable for detailed quantitative measurements. Shown in Figure 15 are the Balancing Circus Man and the Bungee Jumper® with his Killer Tomatoes. The Balancing Circus Man can be used to discuss center-of-mass and stable equilibrium. But, in addition, if it is tipped slightly and released, it can be used to examine oscillations about its equilibrium position. The period of these oscillations can be predicted by calculating the moment of inertia of the toy about various axes. The toy can be assumed to be made up of a variety of pieces (e.g., spheres, thin rods, etc.), and these are just the shapes which are often considered when discussing moments of inertia in a college physics class. The predicted periods of oscillation for different axes were found to give excellent agreement with the measured values. (7) The Bungee Jumper is a toy man on a plastic spring which can be dropped and observed to bounce in the manner of a real bungee jumper. The properties of the spring can be examined by hanging weights on the man and measuring the amount of stretch of the spring. The weights which were used were Killer Tomatoes (which are rather more fun than using traditional metal masses). When a graph of distance versus weight was plotted, a straight line was obtained showing that the spring did obey Hooke's Law, and it had a spring constant of 1.3 N/m. These toys can also be observed in action on the web at http://www.clemson.edu/phys-car.
Shown in Figure 16 are a Magic Animal and an Infrared Blaster®. The Magic Animal is a small plastic alligator which when placed in water grows considerably in size. Its mass increases by a factor of about 30, and its length by a factor of three. This toy can be used in elementary grades to teach the concepts of measurement of length and mass. It can later be used to introduce the concepts of graphing, with bar graphs and line graphs. For high school and college classes it can be used to study exponential growth, semi-log graphs, and curve fitting. The Infrared Blaster is a toy consisting of a gun that shoots an invisible beam and a target that detects the beam. This toy is an excellent one to illustrate the investigation of an unknown. The properties of this "unknown" beam can be measured and compared, for example, to the properties of light. The beam is observed to reflect from mirrors and metal sheets. When the angle of incidence and the angle of refraction of the beam are measured, the beam is found to obey the Law of Reflection. The beam was also sent through a semicircular Plexiglas lens. Again, the angle of incidence and the angle of refraction were measured, and the beam was found to obey Snell's Law with an index of refraction of about 1.4. Finally, the beam was observed to diffract when sent through a diffraction grating, and its wavelength was measured to be about 920 nm. The conclusion that can be reached is that the beam is indeed an electromagnetic wave and is, in fact, infrared light (which is no great surprise, given the name of the toy). (4)
In addition to observing many toys and ideas, the workshop participants were also given the opportunity to perform experiments with the toys. The participants were divided into groups of 3 or 4, and each group was given a toy and asked to devise and carry out an experiment with their toy. Some of the toys used for these experiments are shown in Figure 17. The dart gun was fired horizontally from various heights to see how initial position affected range. The pull-back robot, See-Thru-Racer and explorer gun were all used in experiments that looked at how the amount they were wound affected the distance traveled. Sample results from the latter two experiments can be found in Ref. 2. The electric car was used to produce data for a distance versus time graph. One group investigated the ability of the Push-N-Go® to climb shallow inclines. (8) Another group investigated how the amount of air in the balloon racer, shown in Figure 8, affected the distance traveled. While the time to do these experiments was limited, the groups were all able to obtain some results which were then shared with all of the participants. These experiments demonstrated both how toys can be used in quantitative investigations and some of the difficulties involved in doing this.
The workshop participants were introduced to a large number of toys which can be used to demonstrate principles of physics. They had an opportunity to be involved in both qualitative and quantitative investigations of the toys. In addition to receiving several toys to take with them to their classrooms, the participants carried away many ideas about how toys can be used in the classroom to make physics less threatening and more enjoyable to their students. Physics can be fun not only for students, but also for the teachers. By using toys, physics can be fun for everyone.