Physics graduate student Matt Thrasher and Professor Harry Swinney recently explored the phenomenon of liquid bouncing, where a falling stream of liquid bounces off the surface of the same liquid.
In the video, you will see a stream of silicone oil after it has dropped into a tank of the same oil. The long stream of oil stretches to the right under the surface, because the oil in the tank is moving to the right.
Surface tension creates a bubble of air at the tail end of the stream making it look something like the end of an elephant’s trunk, and the length of the stream begins to shorten under the surface.
The flow rate of the oil in the tank is slowed, and the stream prefers to bounce above the surface, rather than plunge below it. A thin layer of air separating the two surfaces causes the bounce.
Try this at home. You can repeat this experiment in your kitchen with regular cooking oil. Fill a glass dish to 4 cm deep with canola oil. Pour a thin stream of the same oil from a cup about 3 to 6 cm above the surface. While pouring, move the stream in a circular motion or place the dish on a rotating surface, such as a Lazy Susan.
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