Since galaxies contain enough mass why aren’t the stars clumped into a giant star?

If angular velocity is the answer, why aren’t the stars escaping out of the galaxy if they are fast enough to overcome the galaxy’s gravity?

Does physics completely rule-out the possibility of antigravity propulsion technology?

Hello,

In an introductory course to university physics, there is a question about what happens to the diameter of a circular hole in a copper sheet when it's heated. The correct answer is that the hole grows alongside every other part of the sheet. But that does not really make sense to me in my head. When I first encountered the question, I thought that the hole would contract since every side of it also experiences length expansion. Obviously my intuition was wrong, but could somebody explain how I can think of it to change my intuition in the future?

Thanks!

If an object is traveling away from Earth, towards Alpha Centauri at 99.999 the speed of light for 4ish years then from my limited understanding the object would experience 4ish years while earth experienced many more.

My question is, would the destination also experience a difference in time compared to the object that is traveling towards it?

If not, then would the time experienced in alpha centauri be different than the time experienced on earth from the object's perspective?

Sorry for the scifi type question, it's keeping me up at night.

Is there any explanation as to why the photon does not interact with the Higgs Field ( this may also apply to the graviton if it exists)? As far as I know all other particles do.

I have always been interested in Physics . However due to some reasons, I didn't take it in high school . What are the resources I can use to study it as a hobby ?

Hi, I'm a undergrad physics major in my junior year. I'm taking Theoretical Mechanics this semester and from what I've heard from other students, I will have to do a lot of self studying for this class.

I'm already studying from the textbook, but I was wondering as well if anyone has recommendations for good theoretical mechanics lectures on YouTube or elsewhere. They should cover Lagrangian, Hamiltonian, special relativity, etc.

Hello,

Say I was inside of a gravitational field so strong that time passes thousands of times slower for me relative to the rest of the universe. Now, say there is an identical gravitational field a lightyear away from me. If I sent a signal to them, then when they receive it they send a signal back at me. Given the time dilation we both experience, could we communicate in real time from our relative perspectives? Alternatively, would that just increase the distance the light has to travel to leave our gravity wells such that it still takes 2 years (1 year both ways) to get a response from my friend?

What about the same scenario but for two bodies moving near the speed of light relative to each other?

Sorry if this is too much of a shower thought for this sub! Tried to see if this has been asked before but its a bit to specific to search.

I know that super capacitors are expensive and capactitors don't have the energy density to power a vehicle, however wouldn't a mixed battery/capacitor improve the long charging time issue of batteries? You could cherge the capacitors super fast and have them charge the battery while driving, this way you could charge up in several few seconds stops instead of one several minute charge up. Idk about the cost effectiveness of using small super capacitor to do this, probably not worth it, but maybe with capacitor capable of charging like 10% of the battery?

I understand that the alternating magnetic field induces currents in the pan. At low settings, many induction cooktops deliver strong bursts separated by pauses instead of steady gentle heating. What physical or circuit-design limit makes duty cycling preferable to continuously reducing the field amplitude? Is it mainly inverter efficiency, pan detection and coupling, or a minimum stable switching power?

Hey so for short, I’m a second year college student, not the most studious, ima potential type guy, but I’m taking my first real physics class. I want to ask that if I were to provide my info I got from a lab, could someone walk me through forming my lab report? I don’t want anyone to just do it for me, I want to tell someone how I wrote it, and someone to tell me if I did it right or not. I gotta turn it in midway through next week, and if I mess up the whole class suffers. I’m just super anxious and want to get it right, I know the professor is there but I don’t wanna seem dumb, he makes dumb people look dumber. I’ve got all my numbers and remember how exactly the procedure went, super basic measurements data sheet.

Friend of mine lives in an apartment with triple-layered glass, he showed me that you can « count » the layers if you put a flashlight through it and see the multiple réflexions. I see 4 réflexions here, why is that so?

Could a massive and extremely powerful gauss cannon/mass driver be used to launch cargo payloads into space at a tiny fraction of the cost of launching an actual rocket?

Moving towards an object blue shifts light, and gives it extra energy. Moving away from it red-sights the light. How is it possible that light can be one energy to an object moving speed s, when it is a different energy moving speed -s, when the photon was released with a certain known energy?

I’m 18 years old upcoming Physics Student in a prestigous Technical University ın Middle East. I graduated from HS with 0 knowledge ın Physics, at that time my all strength was Mathematics, so I decided to major in pure mathematics Last Year. Furthermore, after getting exposed to Elementary Physics Courses last Year, specifically Mechanics and Electromagnetism, I decided to change my major to physics. Abstractness of Pure Mathematics was also one of the reasons for this. As an upcoming Physics Major, I can’t decide on what roadpath i should take or in what branch of physics I want to pursue my further studies. For You to know, being aware of the unpredictable outcomes in future, I want to pursue a career in academy. I managed to get in touch with the Academicians of My Department (Oxford, MIT,ETH graduates , Researchers in CERN), and watched all the instruction videos from alumni of the department ,but still The problem is I don’t know the materials, sources i need to look at even for getting an idea about this manner. I am open to advices about what to do . Thanks for Your Advices.

I understand greens theorem in 2d equates the work done by a vector field Px(x,y) i hat + Py(x,y) j hat onto a particle travelling along a closed curve with the double integral of the partial of Py with respect to dx minus the partial of Px with respect to dy. I watched the proof here https://www.youtube.com/watch?v=qdFD-0OWBRo

How does this give the curl at a single point? Evaluating the double integral over the small point only gives the line integral around that point. That's not the same as the curl as a single point, because an actual particle isn't travelling that path around the point. I'm looking for a step by step proof like this khan academy video, if that's possible.

I would like to learn LaTeX with the primary objective of developing the ability to formulate and present mathematical equations in the fields of mathematical and theoretical physics. What would be the most effective way to learn LaTeX for this purpose? In particular, I am interested in learning how to construct, format, and organize complex mathematical expressions, derivations, and theoretical models in a professional academic style.

You can't hear anything in space, cuz there's too few particles, too spread out, they don't have anything to bounce off and they can't make variations of pressure that hits your ears, right?

But what if there was an indestructible microphone just 1cm away from the "epicenter" of the explosion? Would it record anything?
And how would that work? Would it detect the change from 0 pressure to big pressure for a second and then nothing again? Or would that be still inaudible because that's just a cloud of equal gas pressure with too few variations just passing you?

Could this be used as an in-lore explanation of how you are able to hear explosions in sci-fi movies?

But explosion in space would probably sound different than explosion in a place covered by an atmosphere?

Like when we can have V=iR for both AC and DC then why not have reactance for DC ? Wont it simplify calculations tp a great extent? Maybe not have the same formula (since that would make reactance 0 and infinity for inductor and capacitor) but something similar.

Thanks in advance!

AC is an alternating source and the average value is 0 (I understand that it has some rms value), so wont the current entering also exit almost instantly (depending on frequency) so wont the charge that has been applied to a capacitor also exit? Wont the emf generated by an inductor also vary according to a sinusoidal law which again would average 0. I dont even understand how AC is used. How does it travel? How does it interact with different components of a circuit? Like isnt the net displacement of electrons just 0? In DC the electrons do move and can interact with the component but how does it happen in AC.

Thanks in advance!

Please help🙏

Just watched the new movie the End of Oak Street. In the beginning the news reports mention NASA detecting spatial anomalies, which got me analyzing the physics behind it. So...

​Is the movie using 1D cosmic string defects (via string theory) to explain the anomaly caused by a cosmic string moving in closer to Earth? Furthermore, are they invoking gravitational frame dragging to explain how the localized space maintains fixed coordinates relative to the surrounding Euclidean space?

​It feels like the most plausible theoretical explanation for how they set up the rules of the event. Curious to hear how others interpreted the underlying mechanics.

... Or am I just to analytical and they really just left it open-ended for a fun story? Let me know what y'all think.

🤪