An ability of cats that has intrigued people throughout the ages is their capacity to land on their feet when falling, even if their legs initially point away from the ground. Cats are able to right themselves in midair, and scientists have studied the reason why and have come up with mathematical models to explain it. Research into the physics of falling cats funded by the National Aeronautic Space Administration (NASA) has generated information useful for astronauts trying to turn themselves around in conditions of zero gravity.
Destin from SmarterEveryDay performs a cat dropping demonstration in the video below and addresses the physics involved in the process.
In the video below, Dianna Cowern (Physics Girl) employs science to scare another YouTube personality, Justine (iJustine). To this end she uses screaming dry ice, a Van de Graff Generator, and a plasma ball. The video is fun, and Dianna also explains the science behind the effects very well. Enjoy!
Since time immemorial human beings have observed the curious phenomena of non-coalescence of drops. This happens when a drop of a liquid comes in contact with a liquid surface and does not merge (coalesce) with the liquid surface right away. Rather the drop may remain as if floating on the liquid surface for periods of time ranging from seconds to milliseconds before finally merging with it. In the video below, I used a straw to pick up a volume of my coffee and gently add drops onto the surface of the coffee. The non-coalescence effect is observed in the drops to various extents, and it can be seen clearly in the part of the video slowed down to 240 frames per second.
Although this phenomenon has been investigated by several scientists spanning a time period of more than 100 years, we still don’t know for certain how it happens. The non-coalescence of drops depends on many variables including the nature of the liquid in the drop and the surface upon which it lands, the chemicals dissolved in them, the temperature gradient between the drop and the liquid, the charge of the drops, and the air pressure.
A current hypothesis is that those areas of the drop or liquid surface in contact with the air phase (interfacial) have a molecular organization that is different from the areas away from the air phase (the bulk phase). Thus the drop and the surface upon which it lands do not tend to mix right away when placed in contact with each other. However, as time goes by, the interfacial layer of the drop and the liquid surface tends to dissipate at the point of contact between them (which is no longer exposed to air), and after it has sufficiently thinned, the water drop coalesces with the liquid surface.
Here is an old trick that you can perform with a candle. Take a lit candle, snuff it out by blowing on it, and bring a lit match in contact with the smoke trail that arises from the candle. As shown in the first part of the video below, the fire from the match seems to “jump” very fast to the wick of the candle lighting it again. In the second part you can see how this happens when the video is slowed down to 240 frames per second.
The reason this happens is that a candle fire doesn’t just melt the wax; it also turns it into gas. When the fire is extinguished, the smoke trail that emerges from the candle carries a significant amount of wax vapor which is flammable. When this smoke trail catches fire, the rate at which it burns is faster than the rate at which it rises from the candle. As a result of this, a flame will “travel” down the smoke trail to the candle’s wick and reignite it.
Pretty cool, eh?