If we are in a room that contains no sources of light at all and the room is also sealed off so no light can enter from outside, then we will experience total blackness, irrespective of the color of the walls or the objects in the room. But we can, in theory, also experience total blackness even if the room has a bright source of light, provided that the source of light is behind us and everything in the room is black such that it absorbs 100% of the light that falls on it, and no light gets reflected back into our eyes. This is because the color of objects that do not themselves generate light is determined by what light they reflect. Objects that appear to be red reflect light that is largely in the red range of the visible spectrum of electromagnetic waves, and similarly for other colors. Black objects are those that do not reflect any light at all in the visible spectrum.
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Suppose that you, law-abiding driver that you are, are going along the highway at the posted speed limit of 70 mph. You see in your rear-view mirror a car traveling at high speed in the lane next to yours. Suppose that car is traveling at 100 mph. At the instant that the other car is right next to you, you both see an obstruction ahead, say a tree lying across the road. You both slam on your brakes to the maximum and you come to rest just before you hit the barrier. What would be the speed with which the other car hits the tree?
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Quicksand used to be a common plot device in adventure films, with people inadvertently stepping into it and being slowly sucked under while others were helpless to extricate them. But it turns out that what is more likely to happen is that as long as you don’t thrash around, you will sink about halfway and stop. But getting yourself out is not easy and requires considerable force. This is what a paper in the 29 September 2005 issue of Nature (vol. 437, p. 635) says.
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I have written several posts recently about investigations into the paranormal. While there is no conclusive evidence for such phenomena, many people do believe in them. I also recently had a discussion with some friends who are broadly skeptics but two of whom told me about events that seemed to have no material explanation. It was clear that they were puzzled by not only what they felt was a lack of a material explanation for the events but that the facts suggested that such an explanation was not even possible.
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(We are bracing ourselves for a severe ice storm today in this region so I am reproducing a blog post from back in 2006, before I moved to this site, because I thought that readers might find it interesting. I have edited it slightly, because tinkering with my writing is something I cannot help. This question formed the basis of an article by Robert Rosenberg in the December 2005 issue of Physics Today, p. 50-55.)

As you can see from this video, this man was reminded that ice is really slippery.

But why is ice so slippery?
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All of us, even if do not suffer from depression ourselves, know people, often many people, who do suffer from it. It is telling that often, when we are informed that someone has depression, we ask whether it is ‘clinical depression’, a term that suggests that it is not some transient phenomenon caused by some immediate factor whose effects may decrease with time (like the death of a loved one), but is instead caused by something that is not just deep-rooted but also based in biology.
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Ever wondered how hedges can be shaped into perfect spheres? Via Andrea James, I came across this video of a company that makes trimmers that can create spherical hedges with specific diameters. The rousing Wagner accompaniment is not included.

When roosters crow at the break of dawn, their sound output is quite prodigious, reaching as much as 140dB levels at very close range. If you get that close, you can damage your eardrum in less than a second. But at even moderate distances, levels can reach 100 dB, close to the levels of a chainsaw. So the question arises as to why roosters do not become deaf from their own sound output. Christie Wilcox writes that scientists intrigued by this question have investigated and found the reason.
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