12:32 AM
4

I'm trying to better understand why helicopters are less fuel efficient per unit distance than airplanes. One argument I keep seeing in other questions on the topic is that helicopters actively contribute energy toward both horizontal translation and maintaining vertical position, whereas airplan...

12:57 AM
5

It is my understanding so far that in this kind of experiments like the one measuring the 4π (i.e. 720° Dirac Belt trick) rotation characteristic of 1/2 spin fermions like neutrons, two neutron beams are polarized via S-G apparatus to the same quantum spin number. The two separated polarized beam...

1:21 AM
2

Wikipedia describes "effective theories" as follows. In science, an effective theory is a scientific theory which proposes to describe a certain set of observations, but explicitly without the claim or implication that the mechanism employed in the theory has a direct counterpart in the actual c...

2 hours later…
3:51 AM
2

Let $A$ and $B$ be two entangled systems. Can someone prove or sketch a proof of why you cant unentangle $A$ and $B$ by only acting on $A$ or $B$ alone? i.e. by only applying $\mathbb{I}_A\otimes U_B$, with $U_B$ unitary.

5 hours later…
9:16 AM
4

I do not understand why potential differences in the electric field in a circuit are concentrated at resistors when the potential, to my knowledge, is purely dependent upon location in the field and the magnitude of the charges. Why is the decrease in potential concentrated at resistive elements,...

4 hours later…
1:00 PM
3

I am trying to build a 5 gallon bucket style chicken waterer. My bucket has an o-ring airtight lid with pour spout and cap. I have drilled a 1/2 inch hole about an inch up from the bottom. The bucket sits in a 4 inch tall catch pan. When I put my finger on the hole and fill the bucket, then put t...

4 hours later…
4:45 PM
1

There is widespread confusion (among learners) about the Bernoulli effect, and I think a large part of this confusion is owing to muddling up cause and effect. So I am providing this question and answer to see if others find it helpful. Let's consider laminar flow (i.e. smooth flow in layers) of ...

6 hours later…
10:34 PM
2

I'm reading R. Wald's General Relativity. It defines a tangent vector $v$ as a function, whose domain is the collection of $C^{\infty}$ functions from a manifold $M$ to $R$, and whose range is the real numbers. It's written as $v:F\rightarrow R$. $F$ is the set of functions $f: M\rightarrow R$. S...