# Search results

1. ### I am confused about the meaning, and value, of kinetic energy

This confusion has lingered in the back of my mind for years now, would be good for me to finally get a grasp on this. Say I have an object currently at rest, and I use energy X to accelerate it to speed v. According to the standard formula, it now has a kinetic energy 1/2mv^2. Now I use the...
2. ### Fluid going through pipe: what is the influence of speed on exchanging heat?

I'm doing a fun home project, and it involves water flowing through a metal pipe, where the surrounding is significantly lower temperature than the water in the pipe. The point of the exercise is to cool the water in the pipe as it flows through it. The question is, what influence does flow...
3. ### I If all of spacetime was created with the Big Bang...

...why do people like Stephen Hawking talk about things/events "before" the Big Bang? If time (as part of spacetime) was created with this event, it also marks the point in time that had no "before", doesn't it?
4. ### Detailed simulation or SlowMo of elastic collision?

I was thinking about Newton's Cradle the other day, and I wondered how those collisions actually look like in detail. Which then got me thinking that my understanding of even a basic elastic collision of two macroscopic objects is weak to say the least. Simplified, the two objects could be two...
5. ### I 1s orbital overlaps with the nucleus, why don't they interact?

Granted, the size difference between a hydrogen atom's electron cloud and its nucleus is a factor of one million (~1Å vs ~10^-6Å), but that's still a significant amount of overlap that, I would think, would trigger the occasional interaction.
6. ### Cos -> Cos -> Cos...

This is of course just a silly exercise on a calculator, but it is intriguing that when operating in either degrees or "grad", hitting the cosine button will converge incredibly fast, whereas in radians it is a lot slower. Anybody have a good idea why?
7. ### Magnetic field = electric field in some reference frame?

This Wikipedia article https://en.m.wikipedia.org/wiki/Relativistic_electromagnetism seems (to me) imply that there is always a frame of reference in which a magnetic field can be rather viewed as an electric field modified by relativistic considerations. Is that always true? That is...
8. ### I The Weierstrass function's' odd qualities

I recently stumbled on the Weierstrass function, whose main claim to fame (as I understand it) is to be continuous everywhere, but non-differentiable everywhere as well. Apparently I was in good company with Gauss' and others who assumed that to be impossible! I guess I'm asking, is this...
9. ### What is some of the worst terminology you have seen?

I assume everybody here has seen terminology in their own field or others that produced a groan upon seeing it for the first time. My "favorite" is in signal processing. There is a common audio transformation that does a Fourier analysis, takes the absolute value at each frequency, and then the...
10. ### What are the practical limits of constructive interference?

The "wireless power" thread made me think of this, but I have pondered it before when it comes to microphone arrays etc You can easily find documentation on the interference patterns N in-line sources of waves generate. E.g. The annoying thing here is that you have infinitely extending lobes...
11. ### I Why are "irrational" and "transcendental" so commonly used to describe numbers

(sorry, the thread title got mangled. It should be "why are irrational and transcendental so commonly used to describe numbers") Is this simply out of the most common ways of how one would try to describe a number? (e.g. first try ratios, then polynomials) Or is there a deeper reason for this...
12. ### In the list of "conservation of X due to symmetry Y" ...

That is, with Noether's theorem, it feels to me the conservation of angular momentum somewhat stands out because the measure is more of a derived one. That is, rotation of something is really more of an interplay between inertia of the constituent particles and the forces that hold them...
13. ### Could PWM be applied to emulate resistance?

This thought occurred to me when reading about class D amplifiers, which essentially "emulates" amplification by very quickly switching on and off. Could one use the same principle to eliminate for example heat losses during impedance matching? IIRC, in the perfect condition of matched...
14. ### A circular current-carrying wire floats in space...

Maybe there's a tiny battery somewhere, just to make it realistic. The wire is also very thin, and thus needs little to no force to be bent. What happens to the wire? Does it twist on itself because each piece of the wire experiences a Lorentz force due to the magnetic field of the wire on the...
15. ### Increasing car efficiency by rerouting airflow?

This is only a semi- serious thread, since I suspect there's a simple back-of-a-napkin calculation that shows this to be infeasible. The idea is the following: a lot of a car's efficiency gets lost in the form of air drag, I.e. forcing the air to go around the car. Could one upscale a...
16. ### I A simple theorem we pondered in our ski lodge... (sum of Fibonacci numbers)

We talked about Fibonacci numbers, and I wondered: Can any natural number be construed by a sum of unique Fibonacci numbers? My guess was yes, and a C program I wrote confirms that to be up to about 2,000, but that's of course is no proof. The best semi-proof I could come up with is that the...
17. ### I How does the Poynting vector factor into a normal circuit?

So, the Wiki page on the Poynting vector has this image: I remember hearing/reading somewhere that the energy transmission in a circuit like this is actually not travelling through the wire, but that it actually happens through the electromagnetic field, I.e. essentially the Poynting...
18. ### Could one build "thermal power lines"?

It just occurred to me that akin to electric power lines, which in the end just connect a voltage differential over a long distance and facilitate power exchange between the two end points, one could build "thermal power lines". That is, a well-insulated cable that internally consists of a...
19. ### Is this an integer programming problem?

At work I am writing a somewhat complex piece of software, and inside it at some point I have to solve the following problem: I have several "streams", each of which has equally spaced points according to a proportionality factor 'a', i.e. X=a*n. Each stream has a different 'a'. As an example...
20. ### How do we know everything in the universe is matter? (versus antimatter)

As opposed to antimatter, that is. The whole search for the asymmetry of matter vs antimatter seems to rest on the implicit assumption that what we observe is matter, not antimatter, no? Is there a way of distinguishing from afar between the two?
21. ### Arbitrarily changing EM fields and their photons

This started with me trying to read up how static electric/magnetic fields are described with photons, but it quickly evolved into the realization that I don't really know how the photonic viewpoint describes *any* changing EM field that isn't a neat monochromatic wave. Some sites mention...
22. ### Regarding the "acceleration" of the EM field

In the thread about EM waves, the EM wave equation \left(c^2\nabla^2 - \frac{\partial^2}{\partial t^2} \right) E = 0 got me pondering. The term \frac{\partial^2}{\partial t^2} E is the second derivative of the field. In a solid-body wave equation, that same term (not with E, but the...
23. ### "Reconnection" of magnetic field lines

This is a bit vague, but I remember reading that during stuff like coronal ejections, magnetic field lines "reconnect". Now, does that not suppose "loose" magnet lines in the process? Which to my understanding do not exist?
24. ### Could you send an object into space completely without fuel?

Was pondering this today. Obviously you wouldn't be able to accelerate a 1-ton satellite to escape velocity, but what about small objects? 11km/s (well, even more, to overcome friction on the way) is very daunting, but if it could be managed you could easily send large amounts into space. And...
25. ### Theories that have the constancy of c as the conclusion?

I understand that the constancy of c is a postulate, back in the day guided by the Michelson experiment and Maxwell's equations. I was wondering, are there any (speculative) theories out there that have this fact as an outcome of something deeper/more basic?
26. ### "Water circuit" equivalents of basic electric components

There were two threads in short succession in this forum about basic electric circuitry (RC circuit, RL circuit), and it struck me that over the years I've been surprised that the "water circuit" analogy isn't used more than it is. That is, in a system with a circular pipe that contains water...
27. ### Boundary absorption when simulating wave equation

I wrote a wave equation simulation in C# a while ago, and while everything works fine, I am running into the expected problem that my simulation boundaries (ie the edges of the grid) reflect the waves coming to them. Obviously I want to keep the grid of reasonable size, so I looked into what...
28. ### Information as the key underlying physical principle

It seems to me, at least when it comes to quantum mechanics, "information" has become the most basic unit. Like, quantum entanglement works to the point that information is extracted, and one can even revert certain things by making sure the information is destroyed. Same with the discussion...
29. ### A question about holography

Hi everybody, first time post/question, hope you're kind with me :) I got a somewhat detailed question about holography: Obviously the very point of holography is to recreate the wavefronts correctly towards the viewer, as in this picture (thanks to Wikipedia) My question is, are the...