This Video Explains The Hour Glass Buoyancy Problem
An hourglass is used to tell time but it can also be used for a pretty nifty buoyancy problem. As YouTuber TheActionLab illustrates when you put an hourglass with the sand at the bottom inside a glass of water it falls to the bottom of the glass.
However, if you flip it around so that the empty side is down, the hourglass does not begin to sink until more sand falls to the bottom. Until then, it stays floating in the water.
This is confusing because the weight of the hourglass does not change. So technically it should behave the same way no matter how you put it in water.
To test this event, TheActionLab weighed the hourglass in both directions. Obviously, it was the same weight no matter the direction of the sand which left us even more perplexed. How could it manage to float or sink based on its direction?
But fret not, the YouTuber does not leave us without an answer. He uses his clear and concise approach to explaining scientific facts to illustrate how friction here plays a role in whether the hourglass sinks or floats. We won't tell you more here. Watch the video to find out what is happening.
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