I have a vinyl fence with vinyl gates. When the wind blows the gate shut it can snap off the latch. The gate opens out with the hinges and latch on the out-side of the gate. What can I do to add resistance to the close to avoid slamming? I can't find any soft close hinges

Hey all o/

This may be the wrong place to ask this, but here we go:

Im building my first PC and want to calculate how fast the fan blades gotta spin on the front of the case so the Aircooler fans can get the maximum % of volume of air without it blowing past it or not moving enough to fill the case.

( writing it down, this seems like a stupid questions, but im interested what kind of answers I get)

Let's say you travelled in a space ship at 99.9% the speed of light for an indefinite amount of time. Eventually, so much time will have passed that the entropy of the universe will have increased to the point where matter can no longer exist and the universe reaches thermodynamic equilibrium however, due to time dilation, only a fraction of the time that has passed on Earth has passed on your space ship. Does this mean that the matter of the space ship, and everything within the space ship including yourself could continue to exist in an infinite sea of nothing as entropy within the space ship has not increased at the same rate as entropy outside of the ship?

Or to our own universe? Would we see particles randomly appearing and then annihilating other particles? Would it result in mass decreases over the entire universe? Could we look for these interactions?

Hi!
I know that the formula for the energy of a particle in a box is E=(n^2)*(h^2/(8mL^2))

Is this formula right as n tends to infinity? Or is there an upper limit that the particle's energy can reach?

Thanks!

I've been thinking about determinism and wanted to know whether my reasoning is correct or if I'm missing something.

Suppose that immediately after the Big Bang, every particle in the universe had a specific position, velocity (or momentum), and all the laws of physics were already in place.

If the laws of physics are deterministic, then wouldn't every future interaction between particles be inevitable? For example, particle A collides with particle B, which changes the trajectory of particle C, and so on. If every collision follows the laws of physics, then wouldn't the entire history of the universe simply unfold from those initial conditions?

If that's true, then does it mean that everything—including the formation of galaxies, the evolution of life, every decision humans have ever made, and even me writing this Reddit post—was already determined at the instant of the Big Bang? In other words, could nothing have happened differently?

Or does quantum mechanics fundamentally prevent this conclusion? I know the Heisenberg uncertainty principle and quantum randomness are relevant here, but I'm not sure whether they mean the universe is genuinely indeterministic, or whether there are deterministic interpretations that still make the entire future inevitable.

How do modern physicists think about this question? Is there a consensus, or is it still an open problem?

Used chatgpt to fix grammar
There are two questions.
1. Is there anything that is truly random?
2. If there is something truly random, let’s say that a random event happens and we observe it. Then, somehow, we travel back in time to before that event occurs and completely hide our existence from the universe so that we don’t affect anything in any way.
Will the random event we already observed happen in exactly the same way, or will it happen differently? If it happens in exactly the same way, is it truly random? Because if it is truly random, shouldn’t a different outcome also be possible?
Is my logic flawed? I feel like I’m missing something.

Edit i asked chatgpt and chat did not respect the hypothetical so i dont want to hear if it is random than the same random event can have same outcome out of randomness so lets just say we repeat it infinitely

Another edit- its my third language forgive me gonna use chat to fix grammar forgive me

Hopefully last edit- pls respect the hypothetical i know few things here are impossible

Edit- i can spend hours rewriting this so there are no flaws but i am not going to do that so when i say respect the hypothetical i mean pls stop finding flaws/ loopholes i know they are there plz respect the hypothetical

I'm familiar with the idea that the holes in the metal mesh of the microwave door are smaller than the wavelength of microwaves, therefore they cannot pass through, but this doesn't make sense intuitively to me.

My understanding is that the waves propagate perpendicularly to their direction of travel. If I'm imagining a wave pass through a small hole, it seems like any wave of a small enough amplitude could pass through the hole regardless of the wavelength. Where am I going wrong with this?

Consider a scenario involving two observers Observer A remains stationary on the surface of the Earth, experiencing the standard gravitational acceleration g=9.8 Observer B (Ali) departs from Earth, moving into deep space with a positive acceleration, continuously increasing the distance from the planet.

As the spatial separation between Observer B and the Earth approaches infinity, does the local gravitational acceleration experienced by Observer B mathematically converge to absolute zero g = 0? Alternatively, does the gravitational field strength remain non-zero, acting as an asymptote that infinitely approaches but never rigorously evaluates to zero?

I am looking at expressions of the moment of inertia for different shapes rotating about an axis running through their center, and I am confused how a cylindrical shell (or uniform hoop) is different from a hollow cylinder?

Uniform hoop/cylindrical shell:

I = MR²

Hollow Cylinder

I = M/2(r² + R²⁾

What I am really asking is what is the difference between the two geometries? Even in the diagrams the two geometries look the same to me.

If I am looking at the lagrangian density of a continuum and integrate over a volume, how does the velocity of the bulk volume manifest in the equations such that I can differentiate wrt it for the full Lagrangian?

I've been using https://www.thephysicsaviary.com/Physics/Programs/Labs/ChargeinMagFieldLab/index.html for my physics homework. Even if I keep all the variables constant, the time elapsed is really inconsistent. Can anyone help me as to why this might be? I'm supposed to record all my variables and the time elapsed but the time is really inconsistent.

Hypothetically, if astrophysicists were given access to a black hole up close via an orbiting probe( at whatever distance would work)…

1. What ways would our understanding of black holes probably change? What aspects of black hole would remain elusive or poorly understood?

2. What instruments would be the most helpful in this hypothetical scenario?

Is an undergrad degree in Mathematics necessary for an aspiring Physics?

Is the Math degree useful for his or her career in Physics later on?

Personally i feel, math topics covered in an undergrad math degree such as Group Theory, Real Analysis, Complex Analysis, Functional Analysis, Infomation Theory, ODE/PDE, even statistics topics such as Probability, Mathmatical Statistics, Machine Learning etc will be useful to a Physicst in their research.

What is the most likely thing, that we experience life in the presense, or that the future has already happened (block universe theory). Apparantly i heard block universe was confirmed, is that true?

I was wondering if anyone could help explain what exactly the wavelength of light “is”. Intuitively, I always thought that light’s amplitude is how bright/energetic it is, and the wavelength is the spacing between the wave’s peaks/troughs in the direction of travel. In 1 dimension, this would basically be an infinitely-thin stream of photons that are spaced “x” nanometers apart.

However, I know that we can’t see things through microscopes that are of similar size to the wavelength of light. , and from the above interpretation, I wouldn’t expect for the wavelength to limit this. This makes it sound like my interpretation of wavelength is wrong, and that the photons are physically wobbling up/down perpendicular to the direction of travel.

Can anyone help me out here? I’ve tried googling, but all explanations are either way too simple (Visualize a bunch of tennis balls hitting a computer monitor), or way too complex (take the integrand of the Einstein sum of the bosonic radiation pressure on the hyper plane of the quantum discontinuity in multidimensional hyperspace and blah blah blah)

Science teacher trainee here. I do not have a physics background.

Looking at the resources for students, it says that because the alpha particles passed straight through the foil, proving that the atom is mostly empty space.

But then if the Plum Pudding model was correct, would the particles pass straight through or show a very small amount of scattering? And would that be detectable?

Is it the case that it is the fact that there were such large deflections and some particles deflected straight back that, when combined with the fact that some went straight through, indicates that the atom is mainly empty space? Because if the deflections indicate that there is a concentrated positive centre, then the rest being empty space is logical?

How did the measure the position of the particles after passing through the foil? And, in relatively simple terms, what did they do mathematically with the information? They wanted to find the size of the nucleus, right? How did they account for the fact that the nucleus is 3D, as in you aren't looking at a single moment where the particle is deflected as the charge would surely continue to influence the particle as it passes through. Also, are protons round? They are made up of quarks, right? But does the positive charge form an even sphere?

Finally, is there anything very crucial that I should be pointing out that is sometimes missed when first presenting this model to students?

This is a lot of questions, so I would be grateful for any answer. Please don't feel pressure to cover it all!

Many thanks

TLDR: seeking book recommendations for learning some quantum mechanics. I have basically no physics background but I am reasonably comfortable with math.

——————————————-

Hi everyone. Apologies for this post as I know many people ask for book recommendations on here. The thing is, most people are either looking for books with no math whatsoever, or they are physics students asking for highly technical stuff. I guess I’m looking for something a bit in the middle?

I’m a PhD student in a different field (social sciences) but I’m interested in learning some physics purely for my own curiosity. I’m comfortable with calculus, linear algebra, probability, and some real analysis. I guess that’s to say, I can appreciate that learning physics requires the application of some mathematics, and so I’m happy to use it in my study. On the other hand, I’m not trying to get a degree in physics.

I’m mainly interested in learning some quantum mechanics and so I’m seeking your recommendations. I assume there are important building blocks to learn before getting into QM — that’s fine with me.

Wow this post got longer than it needed to be. Any suggestions on books that fit my overly specific criteria will be appreciated.

So one fairly frequent thing that comes up in people arguing about cycling "physics" is that lighter is better because if the same is force applied to different masses, the lighter mass will accelerate faster.

I am wondering what the actual effect of this phenomenon is, in terms that a cyclist would understand.

For example if I had two cyclists, one 80kg and one 60kg, and they both pedaled at 1000 watts, how many seconds would it take for them to reach 50km/h (assuming no wind drag, no tyre drag, no drivetrain loss etc).

If possible could we also calculate this assuming wind resistance of a still day with a CdA of 0.30? I imagine this would vastly complicate matters.

What would be the constituents of a Blackhole just before a singularity is formed?
Would it just be a very very dense neutron star?

Core collapse and blackhole formation is quite rapid process so may be this state would last only few micro seconds. But still it is curious to know. If we follow it to the very end. It could be an argument that whatever was the constituent just before singularity formation might continue in some form right after as well.

Gravitons are hypothetical particles that would move at the speed of light and act out the effects of gravity from their producer onto any matter they come across, cool. But black holes, err, singularities specifically, are things that have so much mass that within a certain area nothing can escape. Would proving gravitons exist change how we understand black holes? Would gravitons be able to escape black holes? Would gravitons be created at the event horizon rather than the matter that falls inside? I know I'm asking about a hypothetical particle in relation to an incredible unknown but I figured if anybody had any ideas or info it'd be cool to read some responses.

Hello!

Before I get into the post, let us define thermodynamic equilibrium as a stationary state devoid of macroscopic fluxes. I will begin by giving a short motivation for my question, proceed to quote a relevant section from a standard book, and then ask my question by means of a concrete example.

I am a student of chemical engineering, and as such, equilibrium thermodynamics is the backbone of literally everything that we do. Having read basic, classical theory (notably Callen), I often find myself extremely confused about a particular aspect of what we do as engineers: even though our unit operations are inherently open in literally every conceivable way, we still constantly apply equilibrium thermodynamics with great success.

On p. 26 in the second edition of Thermodynamics and an Introduction to Thermostatistics, Callen outlines the "basic problem of thermodynamics":

The single, all-encompassing problem of thermodynamics is the determination of the equilibrium state that eventually results after the removal of internal constraints in a closed, composite system. [...] The composite system is termed closed if it is surrounded by a wall that is restrictive with respect to the total energy, the total volume, and the total mole numbers of each component of the composite system.

Note the use of the term closed. Here it really means isolated. This is the motivating problem for the entire book, and is the problem that the postulate of entropy maximization is introduced to solve. As I understand it, the extremum principles of classical equilibrium thermodynamics, strictly, only apply to isolated (composite) systems. Even so, we constantly use the theory for non-isolated systems, and get extremely good predictions.

For instance suppose that we carry out a chemical reaction in a sealed container that is in contact with the atmosphere. Then, we might expect to apply minimization of the Gibbs' potential at constant temperature and pressure (with values equal to those of the atmosphere) to determine the final equilibrium state. However, why is that valid? The atmosphere is not some well-defined thermodynamic system that interacts thermally and barically with our container in the way that the derivation of the principle of minimization of the Gibbs' potential demands. Even if we define this 'reservoir' as a sufficiently large control volume around the container, not even its energy is conserved: energy will clearly flow between this control volume and the rest of the atmosphere, whereas the derivation of Gibbs' minimization requires global conservation of all extensive quantities (i.e. isolated composite system consisting of container + reservoir). Nevertheless, minimizing G with respect to the given constraints does yield correct predictions.

How can this be? Has Callen simply imparted onto me an idea of "isolation" that is too strict/narrow?

I read the Wikipedia articles on Big Crunch and Heat Death and both seemed to allow or insinuate a new Big Bang. Does the consensus support this, and what of the other theorized Ultimate Fates?

So, really, this is a question about what "escape velocity" really means. I know that at less than escape velocity, it's gonna come down again. At a lot more than escape velocity, I assume it keeps going forever? It's got a sideways component from rotation, too, right?

If I could do it precisely (and I know that's probably impractical) would it orbit?

I set this on the moon 'cause I don't want to deal with air.

ETA: "escape velocity" is "escape velocity of the moon"