The best book of physics brain teasers


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My guess:

[Spoiler]If the tank is being refilled, then because of the extra weight, the water at the bottom should come out faster due to the increase in pressure.

If the tank is not being refilled, then nothing will come out of the top spout after the water level drops below the spout, so the water at the bottom should still come out at a higher rate. [/spoiler]


No, it’s simple. It’s that one, over there.

Edit: Actually it looks like a fun book. A little too much like homework, perhaps . . . .


Based on my experience with siphons I’d guess that:

the water would flow at the same rate while the water level was above the top hole. If it’s being refilled they’d continue to flow at the same rate. I think the position of the hole in the bucket shouldn’t matter, just the position of the exit point.


I had that book as a kid and loved it. If you do as he suggests and really think about the problems before looking at the answer, it will stay with you for a lifetime. 30 years later as a professional physicist who has taken dozens of physics classes, gotten a PhD, read innumerable articles and books, and so forth, and it is still one of the cornerstones of my physics intuition. I highly recommend it.


There’s no siphon here.
Remember “Water seeks its own level” is true, but says nothing about the speed at which it does so. That depends on a certain other parameter.
EDIT: I suppose it’s easier to see if you place the upper hole half-way down.
The answer on the FutilityCloset page is correct, but the “because” part is probably more confusing than the basic reason.


Assuming the drawing is factual…the upper opening-with-downspout would flow more water because the entire opening is at the same height as the bottom of the lower opening; that is: the lower opening has most (all, really) of its opening higher than the downspout’s opening.


True, though if you experiment with a siphon you’ll quickly see that the position of the “hole” in the body of water doesn’t have any effect on flow, only the level of the exit point, which is why I’d mentioned it. But I now think @thaumatechnicia is right based on the drawing.


It’s a great book. The author, Lewis Carroll Epstein, wrote another called “Relativity Visualized”. I hope these books are still in print. Off I go to find out…


I guess that you are thinking of something like Torricelli’s law:

The thing is, both openings are at the bottom.


It’s a wonderful book for getting an intuitive feeling about the physical world. I remember having several room mates doing their PhDs in physics at MIT some years back, and this is more or less what passing one’s orals was about. (Granted, they were expected to develop intuitions about quantum mechanics, general relativity and other advanced topics that are beyond the scope of this book.)

My favorite problem asked how much speed a car would gain going down a hill if it started at rest as opposed to starting at 20 mph. So much of science is just organized common sense.


The water is going to move faster out of the bottom of the downspout because gravity is aiding the fall of water through the spout, which creates a suction or flushing action.


I figured the two holes would drain at the same rate. Otherwise, you could pipe the output of one hole into the other, forcing it back, and have water going in a circle for no reason.


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