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I have been trying to understand electromagnetic waves, but I am unable to connect the mathematical representation with what actually happens in real life.

As far as I understand, EM waves don't really have a visible “look,” but there should be some physical orientation of the electric and magnetic fields in space, which we represent using sine and cosine functions. What I don't understand is why a wave is represented by a sine function in the first place. Why does it vary like that, and what is actually happening physically?

For example, the electric field produced by a charge decreases as we move farther away from it. So, shouldn't the graph show a decreasing curve as the distance increases? How does a sine function fit into this picture?

In another video, I saw that the sine function represents the strength of the electric or magnetic field. For example, if we consider a time interval from 0 to 2, during the positive half-cycle, the field goes from zero to a maximum value and then returns to zero. During the negative half-cycle, the same thing happens, but in the opposite direction.

If this is correct, does it mean that a charged particle placed at a fixed point experiences an increasing force as the field approaches its peak, followed by a decreasing force, and then a reversal in direction during the negative half-cycle?

But then, why does the field vary like this in the first place? If the source is at a fixed location, shouldn't the field simply decrease as we move farther away from it? I think I might be confusing the variation of the field with time and its variation with distance, but I'm not able to understand the difference intuitively.

What I really want to understand is how an electromagnetic wave actually travels through space. If it travels in a sinusoidal form, what is the physical intuition behind that? Is the sine curve just a way of representing how the field changes, or is there a reason the field naturally varies in this particular way?

I know these might sound like basic questions, but I don't want to just learn the equations without understanding what they actually mean physically.

Given that these correlations cannot be mere coincidence, and that information cannot travel faster than light, how do these two electrons "know" about each other and maintain their correlation?

I have been studying thermodynamics in my high school and have come to know recently that the Expansion of the universe is an irreversible adiabatic process that its entropy will always increase. But how is that and where is even the energy source that is provided as in temperature Internal energy in general classical thermodynamics processes?

See this video of me demonstrating. In words, here's what I'm doing. I cover my mouth and nose with my hands, like I'm covering a sneeze the unsanitary way. Then, I whistle. As I whistle, I flutter one of my hands, so I'm quickly slightly opening and closing the cavity created by my hands. I start with a high-frequency whistle, and I slowly slide the whistle down in frequency as I flutter my hand.

At high whistle frequencies, the heard pitch is steady. But at one specific frequency, the heard pitch wavers with the flutter. In other words, when my hands are closed, I hear one pitch, but when my hands are open, it's a slightly different pitch. The same thing happens if I start low and slide up: the pitch is steady except at that one whistle frequency.

What's going on here? I feel like it has something to do with the wavelength of the whistle relative to the size of the cavity, but I don't think it's resonance, because the tone you hear isn't the cavity resonating, like blowing across a bottle. The tone you hear is just the whistle. So why does it change with an open or closed cavity? And why only at that specific frequency?

Hello, I'm an undergraduate physics student, and for one of my classes I've been tasked with interviewing a professional who has a degree in physics and is currently employed in a physics related field outside academia

It would be a casual, about 20-30 minute interview where I mainly ask about your education, career path and work experiences

I'm hoping to schedule the interview for sometime in the near future, whenever it would be most convenient for you. I'm happy to work around your availability.

If anyone would be willing to spare some time, I'd really appreciate it!

Imagine you are running, and exactly 1 km away is another person running at the exact same speed. He is running towards the same point as you, but relative to you, he is moving in the opposite direction, and his relative speed is 0 km/h. Find the answer.

Hi all,

(EDIT: It unfortunately appears that this paper has since been debunked, as environmental artifacts were not properly accounted for. Thank you to everyone involved in the discussion!)

I came across an interesting paper by P.A. Sturrock, E. Fischbach, et al entitled "The case for a solar influence on certain nuclear decay rates".

As we were all taught, nuclear decay is stated to occur at a fixed (probabilistic) rate. However, this paper and a few others by these same authors find significant (~1%) variation in the measured rate of decay based on the earth-sun distance, and also solar activity, leading to them directly suggesting that neutrinos may influence the rate of nuclear decay. As far as I can tell, these papers seem quite conclusive that decay rates are not absolutely constant, but I had never before heard even a hint of discussion regarding this.

As I understand it, their model suggests that the neutrinos may impart kinetic rotations on the nuclei, and thereby modulate the rate of decay. However, I was wondering why this has never been linked with inverse beta decay (a neutrino being absorbed by a nuclei, and instigating a beta decay). It seems like a fairly straightforward connection, but I couldn't find any work suggesting the concept.

Interestingly, my thought process on this was almost the reverse order of the researchers, whereby I came upon the topic by thinking about if/how solar neutrinos could theoretically impact nuclear decay rates, and hypothesised that you may see a change in decay rates (due to IBD) based on Earths' orbital radius. Then my research came across that paper seemingly affirming the pattern.

Does anyone here have more familiarity with either of these concepts, and could point me towards more discussion/research? This has sent me down a real rabbit-hole, but my physics is a little rusty to dig too much further myself. I would also expect a similar effect to occur around nuclear reactors (massive anti-neutrino sources), but I am finding very sparse and mixed results.

Thanks all :)

I’m enrolled in a research course this term, and my work is on the dynamics of Bloch electron in crystals. It’s mostly semiclassical dynamics, and there’s a lot of work involving Berry curvature.

Marder’s Condensed Matter Physics is one of the assigned books I’ve been given, but because it’s a graduate level book and I don’t have sufficient completed coursework in quantum mechanics, I can’t finish the whole thing myself.

Regardless, I want to get an intuitive understanding of what crystal momentum and Berry curvature are. What is reciprocal space? Is Berry curvature a property of the reciprocal space? What are the closest analogues in classical particle dynamics?

During this process, how do electrons move so easily to another atom? Why don't they fall onto the nucleus, and why don't they collide with each other?

hi, I’m having trouble finding ideas for a high school physics project (it’s a group project) our teacher is very picky and doesn‘t like project topics that would be easier and more efficient for us as students (out of the box ideas if you will)

topics can be anything related to physics but we don’t have a physics lab or any physics equipment so any experiment that involves equipment we the student have to provide it ourselves

topics that we have in our curriculum to give you an idea on what we’re learning:

1/ unit on gravity (basic intro to astrophysics think kepler’s law, cavendish‘s experiment, newton‘s law of universal gravitation, ect)

2/ unit on rotational motion (angular velocity, angular acceleration,torque,ect)

3/ momentum and its conservation (impulse and momentum)

4/ work energy and simple machines

5/ energy and its conservation

6/ thermal energy

I am looking at AP placement on my ceiling and trying to determine if it can reach a IoT device in my attic. I am looking at Ubiquiti U7 Pro XGS and found the AP spectrum pattern for this device.

From what I can gather, I should have pretty good coverage I place my wireless plug 9' horizontal and 3' vertical from the AP. The device uses the 2.4GHz band.

https://imgur.com/a/hOrySN4

Anyone good at reading spectrum maps? From what I can gather through google, I should have pretty good coverage if my IoT device is 9' horizontal and 3' vertical from the AP. At 9' out and 3' up, the device sits at a diagonal angle of approx 72 degrees off the center vertical axis. Near the 60° to 75° mark, the color is a solid, vibrant orange/red.

Just trying to confirm I am reading this correctly, as I am not an RF engineer and not really sure what the charts describe.

I asked this in a scale-visualization post in another subreddit, figured I should ask actual physicists.

Each nucleon is three quarks bound tightly together but the shell model has, well, shells. I can't quite wrap my head around how that works with the very short-distance forces going on in the nucleus.

I always get my friend's kids books for the holidays. Her son is 13, and increasingly fascinated by all things related to physics and cosmology. He's in an accelerated track at school, and reads at a college level, but still has only a middle school math background (I'd hazard a guess that they're somewhere around quadratic equations and the Pythagorean theorem this winter).

Two years ago I got him an illustrated edition of A Brief History of Time + The Universe in a Nutshell, and he reportedly couldn't put it down. Any ideas for a followup that he might find similarly compelling?

EDIT: Wow, I did not anticipate nearly so many responses, and probably can't respond individually to all of them. Looks like I've got a whole bunch of books to check out. Thank you to everyone who responded for all these ideas, and please keep them coming!

I'm reading 'Red Mars' by Kim Stanley Robinson, and came across the line: "Total column mass about 10^-3 grams per cm^-2." (The actual text is more elegant with properly written exponents)

It looks to me that this unit is wrong, using "per" and also using the negative exponent is doing the same thing. Wouldn't you use one or the other?

does the current in plasma globes prefer your skin over air because skin has less resistance?

I heard that a ship moving 99% the speed of light with a light beam in front of it would see the beam move away at the speed of light, while a stationary observer would see the beam pull away from the ship slower. If this is the case, then what would happen if a ship sent light infront of an behind it? Wouldn't the ship always see the light equadistant from itself while a stationary observer would see the front light move away from the ship slower than the back light? How is this possible?

The problem dictates:

Two punctual still masses, M₁ = 4,00·10¹²kg and M₂ = 9,00·10¹²kg, are on x₁ = 0 and x₂ = 1000m, respectively. Only the (gravitational) fields are considered.

a) Draw the fields both masses produce on P coordinate x = 500m. Calculate the resulting field, with its direction and orientation (?).

This is translated from Spanish, and the words it uses, "dirección" (direction) and "sentido" (orientation) mean exactly the same in normal Spanish, so I'm already unsure of what different things it is asking.

Beyond drawing, I'm at a loss on what to do. So I decide to check the solution because sometimes I can decipher what is meant to be done from reading it. But I still do not understand what was done this time.

The solution is:

M₁ ⃗g₁ ⃗g₂ M₂

○----------------------<-----P--------------->------------○

x=0 x=1000 m

--------------500m-------------∖------------500m----------

● Q: x = 400 m; distances between 400 m and 600 m

𝑔⃗1 = − 6,67 ⋅ 10^-11 ⋅ 4,00 ⋅ 10^12 / 500^2 = ı⃗ = −1,0672 ⋅ 10^−3ı⃗ N kg−1

𝑔⃗2 = 6,67 ⋅ 10^-11 ⋅ 9,00 ⋅ 10^12 / 500^2 = ı⃗ = 2,4012 ⋅ 10^−3ı⃗ N kg−1

𝑔⃗ (𝑃) = 𝑔⃗1 + 𝑔⃗2 = 1,334 ⋅ 10−3ı⃗ N kg−1

Its modulus is approx. 1,33 ⋅ 10−3 N kg−1, its direction is the one on the X axis, and its orientation is to the right, towards the bigger mass.

My questions:

1) What does the solution mean with "its direction is the one on the X axis"? Wouldn't that be a position?

2) What does the "Q" mean? What's there for?

3) From my understanding, the thought process was to calculate the gravitational fields of both M₁ and M₂ and then just add the results up to get the field of P. Am I correct?

The power output from a wind turbine is proportional to the cube of the wind speed. This can easily be shown using dimensional analysis.

Similarly, the radius of the shock wave from a nuclear explosion is proportional to the 2/5 power of the time since detonation, as shown independently by John Von Neumann and GI Taylor during WWII in classified documents.

What other scaling laws can be found using dimensional analysis

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Olá a todos! Tenho 14 anos e estou começando a estudar física nuclear por conta própria. Tenho interesse em compreender a física fundamental das interações entre nêutrons.

Entendo que dois nêutrons livres não formam um estado ligado estável nas condições conhecidas, e gostaria de aprender mais sobre esse assunto.

Tenho três perguntas:

1. Quais são as principais razões físicas pelas quais dois nêutrons livres não formam um estado ligado estável?

2. Quais modelos matemáticos ou simulações computacionais vocês recomendam para estudar as interações entre nêutrons e o dineutron hipotético?

3. Quais livros, artigos científicos ou materiais educativos confiáveis vocês recomendam para alguém que está começando a estudar esse tema?

Meu interesse é compreender a física teórica e explorar cálculos e simulações educativas.

Agradeço por qualquer orientação ou recomendação de material de estudo!

This came up as I was explaining to my 12 yo about the why you land at the same spot when you jump in a train. If somebody can explain this in a way to explain the underlying concepts that will be very helpful.

Is it energy or force?

Hi r/askphysics, question about special relativity:

if you were an observer standing (Say on the outer rim) of a disk that was rotating close to the speed of light, what happens in terms of length contraction? I’m trying to reason that since my velocity is basically only in the azimuthal direction (say in cylindrical coordinates) I think only angles and therefore arc lengths would appear to shrink around the observer, and not radii (So objects in the surroundings would not appear closer). Also since the reference frame is non-inertial I’m sure something weird happens with GR in that case, but I don’t know much about GR.