One of the first things I found on the Web were
Alistair B. Fraser's Bad
Science pages. He starts with
It is better to communicate good information than to offer misinformation in the name of good communication.
Be very, very careful what you put into that head, because you will never, ever get it out.
Thomas Cardinal Wolsey (1471-1530)
Ever see
a picture in a physics textbook like the diagram at the
left? (If you have, please let me know! I
put off making this page for two years because I never found
that diagram, even though I know I've seen it in the distance
past.)
The reality is not so.
While it's true that water comes out of the lower holes faster than it comes out of the upper holes, as it has more pressure behind it (directly proportional to the depth of the column of water above it) it's not true that the streams necessarily cross as neatly as in the diagram. Depending on the relative heights, while water from the upper stream is travelling more slowly, it also has a longer time to travel before it hits the table, and the lower stream may not have "caught up" by then. (Discount the middle stream in the photo: it's obvious that a bur or something in the design of the hole is causing the water to leave the cylinder with some upward velocity.)
For a related problem, in which there is a trade-off between velocity and time in which that velocity is useful, see my Swimming Hole (Tarzan) problem.
Note: The cylinder shown was constructed from a one quart can containing baby formula. The garden hose was adjusted to keep the level in the cylinder consistent. Photographed October 1996.
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