Voladores de Papantla
This may look like a simple toy, but the physics is astonishingly complex. Consider that once you’ve added your energy in winding it up, the only force driving it is the earth’s gravity, which always pulls straight down. Most times gravity leads to a downward acceleration but the motion of this device is both downward and rotational and at a nearly constant speed. Furthermore, the voladores (screws) always swing out to a certain angle with the central dowel.
You may conduct small experiments to see what difference various factors make. Some possibilities are to make the voladores heavier (tape two more screws onto each one), use a thicker central stick or wrap the stick with tape or paper to make it thicker, use a larger or smaller cup, tie more or fewer voladores, or make the pole longer. In each experiment you need to have two devices with only one factor changed between them. For example, if you want to see the effect of the weight of the voladores, its best to get two set-ups with the cups, sticks and strings exactly the same, then change just the weight on one of them. Once you have two devices with one different variable, let them go and time how long it takes to get down as well as noting any other differences: the angle that the screws swing out to, how long it takes them to get up to speed, what happens when they are down, etc.
Force that makes something turn is called “torque.” The strings exert torque on the central stick in this project, but the stick is fastened down, so the cup ends up turning. The torque results from the strings pulling on the circumference of the central stick. If they were connected directly to the center of the stick, there would be no motion.
The angle that the voladores swing out to depends on the speed that they turn at, which in turn depends on the torque of the strings, which in turn depends on the weight of the voladores. The rotational speed also depends on the angular momentum, which is determined by the weight and the distance of the weight from the center. So the bigger the screws the harder they pull, but the bigger the screws the harder it is to spin them around. We found the weight makes very little difference in how fast the voladores spin.
The size of the central shaft and the cup on the other hand make a huge difference. If you make the shaft larger by wrapping it with tape or paper, or just using a larger cylinder such as a film can, the torque alone increases and the voladores go spinning down much more rapidly. The same thing happens if you use a smaller cup.
You can wind the toy up half way, cut one of the strings, and then continue to wind it to the top. When you let go, it works fine until half way down when the one volador goes flying to its demise. You can then see what happens to the others. They may still live.
By winding the four stings on the dowel, you raise the screws and give them energy. This energy is called “potential energy,” or stored energy.
The force of gravity pulls screws down to the ground, and makes the cup spin.
When the screws are spinning and falling, they have energy of motion, or “kinetic energy.”
Even though gravity only pulls straight down, the toy spins because the strings put a force on the central stick at its edge. This gives a torque that pulls the cup around.
What would happen if you have only 3 or 2 voladores?
How could you make the voladores spin faster?
What would happen if you had a smaller cup, or larger central shaft?
What would happen to the other voladores if one string broke halfway down?