The Way Toys Work
The Science Behind the Magic 8 Ball, Etch a Sketch, Boomerang, and More
By Ed Sobey, Woody Sobey
Chicago Review Press Incorporated Copyright © 2008 Ed Sobey and Ted Woodall Sobey
All rights reserved.
History of the Aerobie
Lots of toys are invented by someone stumbling onto a design or idea. Not so with the Aerobie. Inventor Alan Adler worked for years to perfect the design and find the right materials to create this flying ring, which can be thrown several times farther than a flying disc such as a Frisbee. Adler, an engineering professor at Stanford University, used his knowledge of aerodynamics to design the Aerobie. Before he invented the Aerobie he invented the Skyro, which set a Guinness World Record in 1980 when it was thrown 857 feet. The Aerobie beat that record when Scott Zimmerman chucked one 1,257 feet in 1986. Scott's throw set the world record for the longest throw of an inert, heavier-than-air object. Although the record was bested a few years later, it remains the world record for an "object without any velocity-aiding feature."
How Aerobies Work
To understand how a flying disc or ring flies, read about the Frisbee (page 52). Aerobies are different from Frisbees in several ways. Whereas a Frisbee has a blunt edge to create turbulence and reduce lift at the leading edge, the Aerobie has a unique lip, or spoiler, on its outer edge to create stability. Its slender profile presents much less drag surface than a flying disc. Less drag allows it to travel farther.
The Aerobie also differs from the Frisbee in that, as a ring instead of a disc, it has an opening in the center. In flight, air moves through the opening so that the inside edge is also a leading edge, which generates more lift.
You can make your own version of the Aerobie and determine how much of a spoiler is needed to get a good flight.
Inside the Aerobie
By looking at a cross section of the Aerobie, you can see features that may have otherwise eluded you. Cut through one side of the Aerobie, as shown here. A coping saw or another saw with a slender blade works well.
Check out the shape. It looks like a wing, which it is. The odd part of the design is the lip, or spoiler, on the outside edge. That spoiler was the breakthrough design feature.
Another problem Professor Adler had to overcome was making the outer edge soft enough that it wouldn't hurt someone who might be hit by it, yet keeping the toy rigid enough to fling. That's why you'll find a dark polycarbonate backbone in the middle of the softer and lighter outer material.
If you want to put your Aerobie back together, glue the cut edges back together with plastic glue. Reinforce the weld by gluing a craft stick to the underside, across the glued edge. It looks a bit odd, but it will fly fine.
Build Your Own
Cut out the centers of several thick paper dinner plates. Fling your "rings" to see how they fly. A few brands of paper plates are made of heavier material; they make for rings that fly well without modifications. Most paper plate rings, however, require some help.
Mount two plates upside down on top of a third, right-side-up plate to form a flying saucer–like toy, and tape them together. Check how this flies. To improve the flying characteristics, try affixing four metal washers or pennies at even intervals along the outer edge. Now try out your creation. Next, try bending up the edges of the plates to make a lip like that of the Aerobie. Adjust the position of the lip until your ring flies level. Then try adding more evenly spaced weights to your ring. The goal is to create a ring flyer that travels far. It should fly level, without either side rising.
You can also create a ring flyer by cutting out the center of an empty pie pan. Adjust its flight by bending the outer edge up or down.
Teachers wanting to incorporate Aerobies and Frisbees into classroom learning opportunities should look at Ed's book Loco-Motion: Physics Models for the Classroom (Zephyr Press, 2005).
History of the Air Hog
The idea of a toy plane that's driven by air pressure and a piston came from inventors in England. The inventors were unable to sell their idea to big toy companies — they hadn't yet made a flying prototype — but they found interest in a young Canadian company, Spin Master. Following the success of two previous toys, Spin Master invested a half-million dollars to develop the idea into a product. Beginning in 1998, sales — like the planes themselves — took off.
How Air Hogs Work
Like all Air Hogs toys, an Air Hogs car has a pneumatic motor. Air pressure — you provide the energy by pumping air into a pressurized reservoir — pushes on a piston. The piston is attached to a crankshaft that converts the linear motion of the piston into the rotary motion of the wheels. Add some gearing and a flywheel to keep the spin going through angular momentum, and the car is ready to go. To control air flow to the piston's cylinder, there are intake and exhaust valves. Each has a tiny black ball that you can see (and easily lose if you take the car apart!).
The car comes with a pump to fill the reservoir. Air enters the reservoir through a ball valve, supported by a spring, that lets air into the reservoir, but not out. When the reservoir is filled and you're ready to play, you spin the left rear wheel (or the propeller, if you have a plane or helicopter). As it rotates, it turns the crankshaft (attached through the gears). The crankshaft pushes up on the piston, which is connected to a spring. The spring lifts the bottom of the second valve to let air into the chamber, driving the piston down.
The crankshaft is attached to a metal gear with eight teeth. It drives a plastic gear with 22 teeth, and that gear drives a third gear with 52 teeth that is attached to the wheel. When a small gear drives a larger gear, which in turn drives an even larger gear, these gears in series slow down the rotation speed (from small to large) but increase the torque, or turning force, that powers the wheels.
Once we took apart the car we were able to estimate that for every turn of the big wheel, the piston completed six or seven cycles. This estimation was validated when we calculated the gear ratio, which is 52/8, or 6.5. (The biggest gear has 52 teeth, and the smallest has eight. Therefore, for every revolution of the wheel, the piston moves up and down 6.5 times.)
Inside an Air Hog
The Air Hogs car is a great toy to take apart. Turn it over to see the transmission. Pushing the lever to the "Power Sprint" side engages both rear wheels to the power train, making the car go straight ahead. Sliding the lever to the "Spin Out" side disengages the right rear wheel so that the car, powered only by the left rear wheel, turns in circles.
Using a Phillips screwdriver, you can loosen and remove the four screws that secure the body to the chassis. Next, disconnect the air reservoir. WARNING: Although you may be tempted to just twist off the air reservoir (clear plastic ball), don't. The reservoir has weak walls that you might damage by squeezing too hard. Instead, use pliers to twist the black collar in order to remove the reservoir.
Turn the car over to remove the four screws that hold the rear wheels and motor in place. With the air reservoir disconnected, you can pull the rear wheel assembly down from the chassis.
Look, from the side, at the valve that lets air in. You'll see a tiny ball supported by a spring. Air from the pump depresses the ball slightly, which allows air to flow into the reservoir. During the pump's recovery stroke, the spring pushes the ball up in place to prevent air from leaking back out. Once the spring has pushed the ball up, air pressure from the reservoir (in addition to the spring) holds it in place.
Slowly spin the left rear wheel. You'll see a white plastic piece — a piston — rise and fall six or seven times with each revolution of the wheel. Air can't escape the reservoir until the piston rises. To get the car to move, you turn the wheel, which moves the piston, which releases air. As the wheel turns, it moves the white piston up to push on another tiny ball that's attached to the large spring. When this ball moves, air escapes from the reservoir and pushes the piston down. When the piston moves down, the spring pushes the ball back in place to block the flow of air. So once you start the wheel spinning, the reservoir delivers a blast of air to the piston six to seven times per wheel revolution. You can hear the "puff, puff" of air escaping when the car operates.
Lightly screw the reservoir back onto the valve assembly; this will hold the two parts of the assembly together. Two tiny screws hold the valve assembly onto the motor. Remove these with a jeweler's screwdriver. Now ask yourself: "Do I feel lucky?" If your answer is no, don't take apart the valve assembly. If your answer is yes, spread a white towel on your workbench to catch the two tiny balls that will soon come bounding out.
Three screws hold the two halves of the valve assembly together. Remove them, then unscrew the reservoir. That will allow the two halves to come apart. Watch one of the balls bounce away as you separate the halves. It'd be tough to find a replacement for one of these, so don't lose it.
Notice the O-ring in the upper half of the valve assembly. O-rings are used in high-pressure devices such as scuba tank valves and space shuttle tanks. Higher pressures squeeze the O-ring, causing it to make a better seal.
Now, before someone bumps the table and those tiny balls are lost forever, put the valve assembly back together.
To access the motor, unscrew the four screws holding the top piece. Lift out the crankshaft (the white plastic piece attached, off center, to the wheel), the metal gear, and the fly-wheel assembly.
When assembled, the crankshaft fits under the piston. When it pushes up on the piston, the piston lifts the lower ball, which admits air that drives the piston down and shuts off the supply of air. To start the engine you have to spin the wheels to initiate the cycle.
The flywheel (the metal disc at the end of the shaft) keeps the shaft spinning. Once it has started to spin, its momentum will keep it rotating, allowing the crankshaft to release more air. (See Friction Car, page 49, for a discussion of another application of a flywheel.)
Finally, you can remove the several screws holding the two halves of the transmission housing together. While the housing is open, count the number of teeth in each of the gears. Now, before you misplace one of the parts, get the transmission back together.
The pump looks well constructed, but is otherwise unremarkable. We recommend leaving it intact.
History of the AstroBlaster
A conversation among physicists at a cocktail party was the genesis for the AstroBlaster, a stack of bouncing balls capable of rebounding to five times its drop height. Bill Hones, his father Edward, and Stirling Colgate share the patent (patent number 5,256,071).
How AstroBlasters Work
According to the patent, the AstroBlaster demonstrates "an unobvious consequence of fundamental laws of physics — the acceleration of an object to high speed by multiple collisions among a series of heavier objects moving at slower speed."
We ran some experiments to understand what's going on. We pulled the shaft out of the bottom ball so we could bounce test it. We dropped each ball to determine its rebound. We estimate that each of the three bottom balls rebounds to about 75 percent of its drop height. Then we tried the top ball. Kerplot. It went almost nowhere, exhibiting about a 20 percent rebound. It seemed that the top ball was made out of a different material than the other three — but we would later find out that this wasn't the case.
When you drop the AstroBlaster, its collision with the ground causes some loss of energy, but not much. Physicists say this is an elastic collision — the total kinetic (moving) energy is the same before and after the collision. Of course, it's not exactly the same. Based on our rebound testing of a single ball, we estimate that it's about 75 percent; the other 25 percent of the kinetic energy is transformed, most into heat energy and a bit into sound.
When the stack of balls hits, the bottom (most massive) ball transfers its considerable momentum to the ball just above it. The second ball now has its own momentum plus the momentum of the bottom ball. When it hits the third ball, it transfers its enhanced momentum to it. The small ball on top is on the receiving end of this substantial transfer of momentum. Since momentum equals mass times velocity, and the top ball is much less massive than the ones below, the transferred momentum manifests as a much higher upward velocity — several times the ball's downward velocity, in fact.
But there's more. The maximum height the small ball can reach is determined by its kinetic energy, and that depends not on its velocity but on the square of its velocity. So the several fold increase in velocity yields a significant kinetic energy change and a much greater rebound height.
But when the balls are bounced separately, why does the top one rebound so much less than the others? We tried to figure this out, and ended up calling one of the inventors. It turns out that all of the balls are made of the same material — polybutadiene, also used in SuperBalls — but the hole in the small ball makes its collision with the floor much less elastic. More energy is lost in the collision, so it rebounds less.
Build Your Own
The AstroBlaster features a great design — a post keeps the balls aligned and allows you to drop them so that they fly straight up. In making your own version of the AstroBlaster you'll lose this property, but you'll still end up with a neat toy.
You need a basketball, a tennis ball, and a lighter ball such as a racquetball. Find a clean tin can that's just a bit larger than the tennis ball and remove both ends. Duct tape one end of the can onto the basketball, and you're done.
To operate it, go outside — this step is important for maintaining domestic tranquility — and put the tennis ball into the open end of the can. Hold the apparatus so that the can points straight up. (This is the time to mention what a great investment safety goggles are.) Release the basketball and watch the tennis ball fly when the basketball hits the ground. Repeat the experiment, this time placing the racquetball on top of the tennis ball. Whoa! Just how tall a stack of balls can you create?
To convince yourself that energy and momentum are transferred from the basketball to the other balls, measure the rebound height of the basketball with and without the other balls. You'll find that the basketball has a lower rebound height when it transfers momentum to the other balls.
Fascinations (800-544-0810) sells the AstroBlaster, as do several science catalogs and Web sites.
For a more complete description of the physics behind the AstroBlaster, see Turning the World Inside Out and 174 Other Simple Physics Demonstrations by Robert Ehrlich (Princeton University Press, 1990).
Balsa Wood Plane
History of the Balsa Wood Plane
The largest manufacturer of balsa wood model planes got its start in a barn in 1926. Paul Guillow founded his toy company just as aviation was becoming popular. The year after Guillow launched his company in Wakefield, Massachusetts, Charles "Lucky Lindy" Lindbergh made the first solo transatlantic flight. Lindbergh's success spawned interest in model planes, and Guillow's business took off. His first models sold for 10 cents. The company continues to make balsa planes, but today it also makes foam and plastic models, kits, and promotional materials.
How Balsa Wood Planes Work
Balsa gliders are tossed by hand into the air or launched with a rubber band. The propeller-equipped model discussed here has a rubber band that is wound up. Of course, it works only if you wind it up in the right direction. Look at the propeller to figure out which direction of spin will catch air and push it toward the rear to move the plane forward. The propeller must be wound in the opposite direction. Or take the trial-and-error approach: wind the propeller up and let it spin to find what direction it moves the air. (Continues...)
Excerpted from The Way Toys Work by Ed Sobey, Woody Sobey. Copyright © 2008 Ed Sobey and Ted Woodall Sobey. Excerpted by permission of Chicago Review Press Incorporated.
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