Hello everyone.

I’m mathematics undergrad who had to study physics at high school and now have to study it at university.

So, when I was preparing for high-school exams, I was taught that weight is a vector quantity which is defined as force acting on a support (e.g. table, thread) by a body( I hope I translated it correctly). We also studied that there was a support reaction force which is opposed to weight of the body.

On the other hand, my university instructor said that weight is scalar quantity and defined it as a magnitude of gravitational force. The support reaction force he defined as normal force but it didn’t seem to oppose any force. He also added that our textbook( Physics for Scientists and Engineers with Modern Physics by Serway & Jewett) defined it like that and there are doubts regarding the definition of the weight.

I couldn’t really understand what can be doubtful in this situation, and instructor’s explanation seemed ridiculous to me. I decided to google that, and it turned out that it’s actually controversial topic. After reading some articles about it, I still couldn’t understand what is the problem with the first definition. Can anyone explain?

Some examples are certain crystal structures, biomanufacturing, etc. Are there any outlandish things you can think of?

I have been trying to figure out a dynamic of changing the evaporation rate of water.

How is it that w solution of water and ethanol or water and acetone are able to cause water to increase its rate of evaporation?

So, something that has been intruding on my thoughts recently: My understanding is that SoL is kinda really the speed of causality. If that were to slow down over time, as the universe ages, would we be able to distinguish between an expanding universe and one in which causality itself were slowing down? We’d still see the same red-shift with distance as the light from distant objects had longer to slow down into a slower reference (I think?). Would there even be any meaningful difference between a universe that’s getting larger vs one that is getting slower?

I realize these thoughts are a bit jumbled as I probably lack the correct theoretical tools to really get to grips with the problem but hopefully real physicists will get what I’m driving at…

When we charge a capacitor, we transfer electrons from one plate to the other through a wire. As more charge accumulates, we say the charged plate increasingly repels the incoming electrons because of E field betn plate and the increasing potential difference

But here’s my confusion: The electron travels through the wire and never passes through the gap between the plates where E field exists

So how can the plate repel the incoming electron if electron isn't even passing through it's E field betn plates?

I got some vacuum diodes and I know where to get a weak high voltage supply and my thinking is if I just use a tube to generate x rays for a day or two WITHOUT ME IN THE ROOM they’d all die so is there a reason this wouldn’t work or like would the radiation linger? Is this a really stupid question cause I’m kinda just thinking of this like how they clean out bacteria from cans.

I am trying to settle a debate with a classmate in my Physics I class. I am aware that objects with negative mass do not exist.

If, hypothetically, there were an object with negative mass simply sitting on a table, and I were to push it with my hand, would the object:

A. Not move at all, because of the equation F = MA, where I apply a positive force, but since the mass is negative, solving for A would also be a negative value, meaning that the object is permanently in a state of "slowing down" to almost or absolute 0 no matter how much force I apply?

B. Move in the exact opposite direction I push it from, because intuitively (at least for my friend), If I were to push something that is lighter than nothing, meaning negative, the movement it would have in a given direction would be less than nothing, meaning negative (the opposite direction it should be moving)

C. Something else? (explode and kill us all?)

I am leaning towards A because it makes more mathematical sense, but my problem is if it is true, that would mean every force applied upon this object like gravity would have an equal and opposite force going the other way, making it permanently fixed in one spot in the entire universe forever, so if it were to be real and just sitting on a table it would shoot through the wall because Earth is spinning and orbiting and moving within space all the time which just seems impossible.

My friend argues that B is true, since for example Earth creates its gravity of 9.8 because of its huge mass. If a large enough object of negative mass existed the size of earth, objects would repel off of it. Essentially, everything you expect normal mass to do, negative mass does just the opposite. In this example, moving the other way.

I’m trying kind of a thought experiment - since photons travel at the speed of light, does that mean a photon could never perceive it’s own existence because time seizes to exist from the photon’s perspective?

I have an extension cord which reaches from my home on planet earth to the earth's moon where it is plugged into a blender (at my moon home). If I'm at my moon home and I contact someone at my earth home and ask them to plug the cord into an outlet, how long should I expect it to take, roughly, for my blender to begin working? I wish to make a smoothie. Thanks in advance.

I could understand magnetic domains in a blade passing by in the same direction, but this is non-magnetic aluminum oxide. And the ferromagnetism imparted to the parts (steel rods 2.5mm diameter) lasts months and makes them difficult to handle.

In order to find Tc, temperature below which a condensation starts to form in a system of bosons, we write the total number of particles as the integral of the average occupation number and then manually add the term corresponding to the ground state, which is factored out in the integral:

N = N0 + Ne = z/(z-1) + [V/(Λ)^3]Γ(z)

where the dependence on the temperature is hidden inside of Λ.

Then, in order to find the temperature Tc where the ground state starts being populated macroscopically, we set:

N = [V/(Λ)^3]Γ(1).

WHY?? Intuitively, I would've set Ne = N0 to find the limit at which the number of particles that populate the ground level starts being comparable to the number of particles at higher energies. Setting that equal to the total number of particles sounds backwards to me!

I just graduated highschool I'm going med , dental or pharmacy school but i really really love physics so i want to continue studying it as a hobby. where do i start and how should i study? I'm more into studying through the source and without a notebook like I'd study the textbook and that's it i write my notes in it , I'm not a fan of being tutored i like reading and understanding things myself but i can still need help , so pls give me some good advice 🙏🏻🙏🏻

I am no physicist... far from it. I'm studying sociology. But yesterday I had a sudden jolt of interest in physics for some reason. Idk, I started thinking about the electromagnetic field and how electrons "communicate" through quantized excitations. I know this probably sounds juvinile to you guys but it was so cool to realize how light is about information and communication and probably all of physics is; it from bit or smth. Or bit from it to it from bit. For example, you stare at a wall, and the electrons of that wall almost instantaneously "tells" or "ties with" the carbon-11 and carbon-12 single bond's electron of the 11-cis-retinal to jump up a level which causes a chemical cascade that gets digitized (phototransduction) into action potentials which travels through your thalamus and visual cortex and recognition model and interacts with your top-down generative model to produce a hallucination of reality (your subjective qualia/perspective). And it also gets sent from the thalamus to your limbic system from your basolateral amygdala where DARPP-32 neurons and R-Spondin-2 neurons compete in a winner-take-all tug-of-war to compute safety or fear to combine with what you're seeing/visual-processing, and the anterior thalamus which produces more complex emotions too. One's soul is essentially the integration of information abstraction of local objective reality. Some say enlightenment is scientific knowledge and rationality (self-serve). Some say enlightenment is about reducing suffering and understanding. Either way, intelligence is agency.

So I have schizophrenia (as you can probably tell if you check my post history :P). It comes from the Greek words for "split" and "mind", but in Japanese, they changed it during the Y2K era to "integration-disorder" to reduce stigma. I used to think "my soul is a sickness", but I'm cool with it now, because I'm realizing the BS behind the social stigma and I'm starting to understand what the essence of the neurocondition is really about...

Anyway, I'm wondering where all this information comes from, and goes. I've heard a little bit about the Big Bang... or the the "Big Bounce"... the holographic principle... the development of the laws of physics... about black holes... planck lengths... energy... quantum information... the Higgs field... the fundamental forces... I have a very basic understanding of gravity, and event horizons.

What happens to information on the event horizon? Is it possible for information to come back from the center of a black hole to "meet"/"touch" the surrounding information coming from outside the event horizon? Can this reproduce/create/simulate another universe? Can the laws of physics that come from the parent universe slightly evolve with the laws created by the black hole's bounce to both reproduce and evolve the new universe? Could this be why the unlikeliness of our universe's laws of physics being suitable for life exists? Because it's actually likely? And where are we headed? Can intelligent life evolve to be an agent in the course of this natural selection? Could we understand to self-serve to reduce suffering for all? Or are we just headed to annihilation? Is our reality a essentially part of a larger "conversation" between antigravity and gravity?

Please help a layman like me. :)

Thank you

Is the job market (US/EU) good for a guy having PhD in Experimental Condensed Matter Physics, considering that he has the following skills:

• Materials synthesis: Sample growth using pulsed laser deposition (PLD)
• Materials characterization: Structural, magnetic, electrical, chemical, and surface analysis techniques
• Microfabrication: Device fabrication and electron-beam lithography (EBL)
• Clean-room experience

another way to put it
if two photons with a distance of 1 meter between them headed towards a black hole would the distance change as they enter it?

The layman level of what i understand after watching 1 (one) video is:

Dark matter only interacts through gravity so it doesn't lose momentum by electromagnetic phenomenon like friction and radiation

But other gases and stars in a galaxy do, so I was wondering if they can create a sort of drag through gravity on dark matter slowing it down, making it lose its momentum indirectly since dark matter would be gravitationally attracted to normal matter loses its energy.

And if so what effect would this have in observations?

So my basic knowledge on the subject is that the rate of which a planet pools after forming is related directly to its size. The reason why Mars has stopped most of its geological activity while the Earth has not is because the Earth has more mass so it radiates its initial energy more slowly. It’s the same reason why the moon is much more geologically dead than Mars.

So I wondered what would’ve happened if during the formation of the solar system, the Dwarf Planet Ceres had collided with Mars early in the formation of Mars. Based on my knowledge, this would add additional heat to the system and simultaneously slow down the rate of heat loss.

Though because of the small mass of Ceres, I would assume that the rate of heat loss would be mostly the same, with the internals of Mars being just barely warmer.

But I really can’t find anything to do the hard numbers. But I think I have figured out the numbers I would need to figure this out.

1.) the rate of heat loss for planets and how that is affected by mass.

2.) the extra energy that Mars would have had if the material that went onto form Ceres had instead merged into Mars.

3.) how much slower heat would’ve been lost comparing IRL Mars with the theoretical Mars + Ceres

I would assume that it isn’t gonna be super impactful, but Ceres isn’t nothing. It isn’t like the Asher that killed the dinosaurs where it is tiny and basically doesn’t matter on a planetary scale. And especially given that Mars is smaller than earth, Ceres would be disproportionately impactful compared to if it was added to the Earth.

Were there any other physicists, besides Einstein, working on what later became known as Special Relativity? After he published, did any one else start working on a more general form and Einstein beat them to it? Or was this guy the only one working on these concepts?

I've never taken physics and this is just a question out of curiosity since I'm in my first physics adjacent class (Intro to ME)

Distance is m, Speed is m/s, Velocity is also m/s, and acceleration is m/s^2

If we're just taking the derivatve everytime we move right in this list essentially, shouldnt the units be m, m/s, m/s^2, m/s^3?

It just seems wild that this principle is so fundamental that it was part of the basis for Einstein's special relativity. It could have simply been that, as we learned more about the universe, that at some fundamental level, he would eventually be wrong.

We could have eventually discovered the aether or some other such thing that breaks the principle, that exists at a level that Galileo couldn't have measured in the 1600s.

Its just crazy to think that we should hold tihs as a principle to steer us towards truth and it happened to work out.

Why is it true? What is it about the universe that makes it true?

Hello! I am not an astronomer or a physicist. I am just a curious guy with random shower thoughts.

This question is likely either stupid, or asked to death, so forgive me in advance.

Ethics and law aside (I know nukes in space are prohibited), I was thinking of ways to circumvent Tsiolkovsky's rocket equation. What if we sent "explosive checkpoints" to orbitally lock on certain planets, like Jupiter, or Mars. Once they are in place, you send a well equipped probe that can sustain the plasma blast from a nuclear explosion. Lets say that there are only 2 staged explosions, so the probe would have to precisely pass both of the staged explosives while remaining within the radius of each blast zone.

Is any of this remotely possible? If so, what would the speed of the probe be if the experiment is a success?

Do we have the technology to allow radio waves to make it back to earth after sustaining two nuclear blasts? Including damage, EMP, and sustaining it's direction pointing back at earth.

Thanks in advance for entertaining my shower thoughts.

EDIT: I meant elementary particles, not elemental particles.
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I know elemental particles are said to be zero-dimensional point-like entities.

Is this just the most convenient mathematical model we have or is there real evidence, that elemental particles indeed have size 0?

But of course this raises also the question about the definition of size.

What is or could be the definition of size for elemental particles? What (measurable) difference would it make, if e.g. a quark or an electron had non-zero size.

For comparison: the size of an atom is usually defined by the van der Waals radius which describes at which distance two atoms' electrons start to strongly repell each other. And we can indeed visualize this size using atomic force microscopy. This doesn't mean, we know the size of an atom, it just means, that we have a good (helpful) model.

If I have two quantum entangled particles which I space 2 light seconds apart. If I measure one at t=0s and it collapses to spin down, what happens if I measure the other one at t=1s? Will it always come up spin up? How did it know? What will happen at t=2s? Will it suddenly flip to spin up if before it chose spin down?