
The Froude number and bipedal locomotion - aidanrocke
https://paulispace.com/robotics/2018/10/26/froude.html
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lordnacho
[https://en.wikipedia.org/wiki/Buckingham_%CF%80_theorem](https://en.wikipedia.org/wiki/Buckingham_%CF%80_theorem)

If you want to get into how things scale, this is essential. You might have
heard someone say "the real equation is dimensionless". Well there's something
to it.

There's a bunch of flow related stuff that ends up being all about dimensional
analysis. Basically, things aren't as simple as multiplying all the quantities
by a constant.

Probably the one everybody's heard of is "what would happen if animal X were
bigger/smaller" -> weight goes up ^3, but cross section of legs ^2. Heat
escapes ^2 but is generated ^3.

~~~
marmaduke
In a lecture on scaling laws, a professor once explained that an early study
of LSD gave the drug to elephants with doses based of relative heights of
elephants compared to humans. The elephants died from the overdose. Scaling a
dose based on height was inappropriate.

~~~
tlb
Back in the 90s, I (and many people) believed that when the Internet gave
everyone instant access to all the world's information, urban legends would
die out because it would be so easy to fact check things and surely nobody
would spare a few minutes of research to avoid propagating a half-truth. Alas,
this theory didn't fully account for human nature.

A grounded version of this story (if you're curious) is given at
[https://erowid.org/chemicals/lsd/lsd_history4.shtml](https://erowid.org/chemicals/lsd/lsd_history4.shtml)

~~~
nanomonkey
TLDR: it's uncertain if the elephant died from the LSD or from the massive
amounts of thorazine and barbiturate that were injected into his ear in an
attempt to counteract the effects of the LSD overdose.

~~~
marmaduke
Ah interesting. That part was surely left out by the professor.

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theothermkn
The Froude number appears to be a dimensionless parameter. Dimensionless
parameters and the Buckingham Pi Theorem are fundamental to physics, and
especially fluid flow. It boils (ha!) down to the ideas that 1) A fundamental
law of physics must have consistent units, and 2) Dimensionless quantities
function as similarity parameters. The Reynolds Number is arguably the most
famous of these (alright, Mach number <sighs>), the ratio of inertial to
viscous forces in a fluid flow. ("How much like water divided by how much like
honey" is a pretty good heuristic.) You can actually _derive_ fundamental
physical laws through dimensional analysis. Powerful stuff. One could do far
worse than tracking down as much as one can about these principles as early in
one’s engineering or scientific career as possible. It’s as big a shortcut in
the hard sciences as Latin is for medicine.

