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In the video below, Dianna Cowern (Physics Girl) shows the interesting thing that happens when the flame of a candle is exposed to falling. While I understand the need to make the science accessible and fun in a short video, Dianna describes the effects of freefall on the candle flame to be a consequence of “taking away gravity”, and she also says that, “Falling towards the Earth pulled down by gravity, is just like floating out in space with no gravity at all”. Neither of these things is true. The gravity that we are talking about, is that produced by the Earth. To “take away gravity” or to “have no gravity”, the Earth would have to disappear! What really happens during freefall that gives the candle flame that shape is that the forces that oppose gravity are diminished or nullified. Because this eliminates buoyancy, hot air can no longer rise. This is counterintuitive, and visualizing it is more complicated and difficult to explain in a video, but if you are interested, I wrote a post about it here.
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Newton’s Cradle is a device that is used in teaching to demonstrate the physical laws of conservation of energy and momentum. The device consists on a series of spheres suspended from wires. The spheres are pulled and released, and then collide with each other. But there must be something charming about Newton’s Cradle which has made it transcend the classroom, as it is used is also used for entertainment, or as a decorative toy, and has even been featured in movies. When the moving ball collides with the stationary balls, the force is transmitted through the stationary balls to the ball on the far side. Depending on the number of moving balls and stationary balls as well as their location and the timing of release of the balls, several recurring collision patterns can be generated as shown in the video below. If you have the time, there is even a computer simulation of Newton’s Cradle that you can operate without having to deal with the effects of friction which eventually dampen the performance of the real device. In this video you see a pilot pouring water into a cup while the plane is doing loops. At one point the water seems to be flowing away from the Earth below him or remains in the glass even while the plane is inverted. What happened to gravity? Aren’t things like water supposed to “fall”? Gravity thankfully is alive and well. What is happening is that the looping motion of the airplane generates a force directed towards the bottom of the plane. This force, called centrifugal force, is strong enough to counteract the force of gravity and make the water stay in the cup or even “fall up” (from the point of view of the camera) while the plane is upside down during the loop. You can see my demonstration of this force in the video below. My demonstration is not perfect in that to spin around the cup my arm has to produce a twisting motion that sloshes the soda around and generates foam, but the principle is the same. In the case of the video of the airplane, the motor propels the plane, and the navigation controls inside the cabin lock it into a circular path which generates the force. In the case of my video, the muscles in my arm propel the cup, and my grip on it locks it into a circular motion which generates the force. Americans have forgotten what it was like to live in the United States before vaccines. One case in point is polio. Whereas this disease did not kill a large number of people such as was the case with tuberculosis or influenza, it left a certain percentage of those afflicted permanently disabled, and these tended to be young individuals; often children. Thanks to the polio vaccine, Americans today do not have to live with the fear parents experienced in communities afflicted by polio. Among those infected by polio who became disabled, some required a permanent aid to breathing called the iron lung. Only a few survivors of that era that still use iron lungs remain today. The video below features the story of one of these survivors, Paul Alexander. Even though world polio cases are at an all-time low, there are still some countries in the world where continuous person to person transmission keeps taking place, and they can serve as a repository for the disease to make a comeback if vaccination were allowed to lapse. The German physicist Georg Christoph Lichtenberg discovered what are today known as Lichtenberg figures. These fractal-like figures are formed when electricity moves through an insulating medium. The electric current tries to find the best route to flow through the medium and in doing so creates multiple branches similar to the pattern made by the roots of trees. Lichtenberg figures are often generated when lighting strikes things such as a golf course or even the human body! The Lichtenberg figures produced in the skin after a person gets hit by lighting are not a burn. They are produced as a result of degradation of the skin with leakage of red blood cells to the superficial layers and normally fade within a few days. If you have the stomach for it, you can check some Lichtenberg figures produced in the bodies of people struck by lightning by clicking on this link. Lichtenberg figures are also used to produce awesome art as shown in the video below. |
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