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Today I will address a question/meme that has been around for decades, and resurfaces every now and then to create controversy.  So the question/meme is: if an airplane is on top of a conveyor belt as wide and long as a runway, with such belt being designed to match the speed of the wheels of the airplane moving in the opposite direction, will it be able to take off? This question has generated multiple debates in the communities of both science and laypeople for many years. The question even inspired an attempt to test it in the television program series Mythbusters where its hosts, Jamie Hyneman and Adam Savage, found that the airplane was able to take off from a tarp that was being pulled by a vehicle in the opposite direction. However, many people claimed that this was a bogus test because the vehicle pulling the tarp did not precisely match the speed of the wheels of the airplane moving in the opposite direction. As to the original question, initially I thought the airplane would not be able to take off. I reasoned that if the conveyor belt can exactly match the speed of the wheels, the airplane would not be able to move forward to generate the wind speed necessary for the air flowing around the wings to generate lift. However, I realized that I was thinking about the wheels of an airplane much in the same way I think about the wheels of a car, and this is a mistake. Let’s compare a car vs. an airplane on a conveyor belt that moves in the direction opposite to the movement of the car/airplane matching the speed of the wheels. In order to advance, the car needs friction between the tires and the ground (traction). A car on a very slippery surface will just spin its wheels hopelessly. So by moving in the opposite direction, you can imagine that the conveyor belt essentially nullifies traction for the car. In the case of the airplane, friction between the wheels and the ground is not needed for the airplane to advance. This is why airplanes on skis can take off on runaways made out of ice and snow. The motor of the car pushes against the ground via the wheels. Its forward movement depends on the wheels and their friction with the ground. On the other hand, the engines of the airplane push against the surrounding air. Its forward movement does not depend on the wheels. The airplane’s wheels are passive – they spin freely. The conveyor belt will not slow down the plane. Although this made sense to me, I still had problems visualizing the situation, because in my mind every turn of the wheel is matched by the conveyor belt moving in the opposite direction, so how can the airplane possibly move forward? Then I realized that the conveyor belt will also make the wheels of the airplane spin due to the friction between the wheels and the belt. In which direction does the conveyor belt make the airplane’s wheels spin? If you look at the airplane from the side, say with the nose facing your left and the tail your right (wheels down, of course), the airplane will be trying to move from right to left, the conveyor belt surface will be moving from left to right, and the wheels will be spinning…counterclockwise. In other words, in the direction of the airplane’s movement! But here is the problem: when the airplane moves forward, it will also make the wheels spin in that direction. Therefore, the speed of the wheels will be a result of that caused by the airplane plus that caused by the conveyor belt. This creates a problem in the basic premise of the problem. For example, if the airplane accelerates, making the wheels spin forward at say 100 revolutions per minute (rpm), and the conveyor belt accelerates in the opposite direction to match the spin of the wheels at 100 rpm, then the combined (total) forward spin of the wheels will be 200 rpm (100 + 100). And if the conveyor belt accelerates to match that total speed (200 rpm), then the final speed of the wheels will be 300 rpm (200 + 100). So we have an impossibility. Even if the conveyor belt accelerates to infinity, it will never be able to match the total speed of the wheels because it will always add an extra amount of spin to them! Of course, if the conveyor belt moves instead in the direction of the airplane’s movement, which will make the wheels spin backwards (against the movement of the plane), it will be able to counter the spin of the wheels, which will remain stationary. But then the conveyor belt will just keep accelerating and dragging the airplane along until it takes off. Finally, if you are curious about applying my reasoning above to the case of the car, consider that the car’s wheels are not freely moving. Only the motor of the car can move the wheels. The conveyor belt moving in the opposite direction will not make the car’s wheels spin forward. It will not add an additional spin to the wheels. So in the case of the car, the conveyor belt can match the speed of the wheels. Of course, if you put the car in neutral (disengaging the wheels from the motor) and attach a jet engine to its roof, you will end up with a situation similar to that of the airplane. Although thinking this way made sense to me, I went online and found that communities of scientists had tackled this question before and conducted computer simulations. The long and short of it is that, yes, the airplane indeed will take off. Nevertheless, there would be insurmountable problems in trying to test the question in a real-world situation where a conveyor belt tries to exactly match the speed of the wheels. The conveyor belt and the wheels of the airplane would accelerate to speeds so great that it would destroy them, and the conveyor belt would move so fast that it would begin to generate a wind current against the airplane that could provide a certain amount of lift. This concludes my foray into the Airplane on a Conveyor Belt conundrum. What do you think? The drawing of the plane on the conveyor belt belongs to the author and can only be used with permission.
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5/17/2024 The Emotional Perils of Child Testimonies and the Potential for Descent into MadnessRead NowBack in 1691 in the town of Salem in Massachusetts, a group of girls started exhibiting strange behaviors including altered speech, convulsions, and trance-like states. The local physician examined the girls and concluded that they were victims of witchcraft. The town’s government accepted this diagnosis and asked the girls to name their tormentors, whom they proceeded to jail and try in court for witchcraft. Salem spiraled into madness as the girls’ accusations placed hundreds of innocent people in jail with twenty of them being led to the gallows. One could look upon this case as an incident from a long-gone era when people still operated based on superstition, as science had not yet studied mental illness in its many facets. However, there are some leftovers from these times that still linger in our societies.  I saw a remarkable documentary on Netflix called “The Outreau Case: A French Nightmare”. It all began in 2001 when social workers raised concerns about the behavior of the children of a family that lived in the town of Outreau in France. The children were questioned, and evidence of sexual abuse by their parents emerged. When the children were examined by phycologists, they were deemed to be credible witnesses. The prosecution of the case was carried out by a young and inexperienced magistrate who was eager to make a name for himself. After the parents were arrested, they confessed to the charges, but then the mother implicated other people in the abuse, which was in turn supported by additional testimony from the children. This was followed by more accusations and more confirmatory statements from the children, which escalated into a vicious feed-forward cycle that implicated more than 40 adults and identified dozens of more children as potential victims of abuse. Of the adults named in the testimony of the mother and the children, a dozen were arrested and held in jail for periods of one to three years. The whole affair was chronicled by French newspapers with sensationalist headlines about a vast pedophile ring which sparked outrage. In a bizarre twist, one of the persons implicated testified that he had witnessed the murder of a little girl, which fanned the flames of the scandal, but the alleged girl’s body was never found. After five years and two trials, where the mother ultimately admitted to lying when she implicated others, and where some of the children also admitted to lying or their testimonies were found to be rife with inaccuracies, all the extraneous people implicated in the crime were found not guilty. One of the defendants died while in jail, and the lives of the others were wrecked with some people being ostracized by family members, friends, and acquaintances, and losing their jobs and their businesses. At the same time, the outcome of the case sparked claims of a coverup and related conspiracies. The United States had gone through something similar during the 1980s and early 1990s with the day-care child abuse hysteria during which many day-care providers were accused and some were convicted of child abuse based on the testimonies of children. The children in these cases were taken away from their parents and repeatedly and aggressively questioned by overzealous police and social workers in ways that ended up manipulating their memories. Some children ended up testifying that they were forced to participate in orgies, and that they witnessed people partaking in satanic rituals where they killed babies and drank their blood. This led to fear-inducing headlines in newspapers across the nation that just fueled the panic. In the vast majority of the cases, the people arrested were not convicted, and those convicted had their convictions overturned, all due to lack of any evidence that corroborated the testimony of the children. The aftermath of the case left a trail of broken lives and lingering social distrust. Whether children’s testimony is more reliable than that of adults has been a very controversial topic in the psychological and legal fields. The early view that children’s testimonies are inherently more unreliable compared to those of adults has been revised in recent years. However, there is ample experimental evidence that children can be induced to recall things that did not happen or even lie when repeatedly questioned in a biased manner under coercive situations by parents or authority figures. For this reason, it is important that those questioning children follow specific forensic interviewing protocols which take into account the age and language capabilities of the children. This is also important because real pedophiles in their defense will poke holes in the testimony of children if it was obtained inappropriately, which could allow them to go free. The Outreau case involved an overzealous magistrate who was willing to accept the accusations made by the mother of the children, who in turn was willing to keep telling him what he wanted to hear. The day-care sex abuse hysteria in the United States involved prosecutors and other individuals determined to find what they were looking for even if they had to coerce it out of the children. However, one of the greatest problems I see in these cases, at least in the initial phases where arrest warrants are issued and suspects are indicted and jailed awaiting trial, is the uncritical acceptance of the testimony of children. In our societies child abuse is a very emotional topic, and children are often viewed as paragons of innocence. When a child upon being questioned seems to provide evidence that implicates an adult in wrongful conduct, the visceral emotional reaction of many people favors the uncritical acceptance of the child’s testimony regardless of its context, how it was obtained, or whether additional corroborating evidence is present. A recent resurgence of the emotionalism characteristic of this mindset was the QAnon phenomenon of a few years ago when millions of people ended up believing that there is a worldwide cabal of satanic cannibalistic pedophiles that includes prominent political and entertainment celebrities. I debunked all of the QAnon claims and even engaged several of these individuals through social media, but it was pointless. As soon as you questioned their claims, they would accuse you of being part of the conspiracy! Now imagine if QAnon adherents had been in a position to fully wield the power of the judicial branch of our government. From Salem to Outreau, the day-care child abuse hysteria, and QAnon, the potential for descent into madness over the emotional issue of child abuse is still ever present in our societies, and now it can be easily amplified many times by the far-reaching power of the media. Thankfully, we have past experience and scientific studies to guide us in implementing the proper methods to deal with child witnesses and to identify testimony that has been wrongfully obtained or which is unsupported by evidence. The child abuse image by Nick Youngson from Pix4free is used here under a CC BY-SA 3.0 license. |
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