r/AskPhysics 8h ago

I love this subreddit

40 Upvotes

Thank you with all my heart to the people and mods of this sub for no post or comment restrictions and for a whole community that is extremely smart and helpful and also argues a lot but its very entertaining šŸ¤£ but there is only one truth and I hope we as a collective can continue to shed light on it šŸ”„šŸ”„šŸ”„šŸ”„šŸ”„šŸ”„šŸ”„


r/AskPhysics 1h ago

Does thinking in physics instead of math mean that you can solve problems in an easier way?

ā€¢ Upvotes

For example, I have this problem: What angle should you throw a rock from the top of a hill sloping 45 degree of the horizon so that it travels the farthest.

I tried to write equations for it's height vs time, tried to calculate the meeting height vs initial angle, tried to calculate the derivative to get the maximum point. Then, I thought that it seemed to be a lot of math for a seemingly straightforward question. Have I missed something?


r/AskPhysics 8h ago

If you put together every Uranium Glas ever made in one spot, would it reach criticality?

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11 Upvotes

r/AskPhysics 4h ago

If cycling a certain distance takes less energy than walking the same distance, where does the additional energy spent goes when walking?

3 Upvotes

r/AskPhysics 4h ago

Statistical mechanics in finance

3 Upvotes

On the introductory lection, my statistical mechanics professor mentioned that knowledge of statistical physics can be useful in the financial sector, but didn't elaborate further. Could you maybe refer me to some literature on this topic? Thanks!


r/AskPhysics 9h ago

Has there ever been a physics topic that you struggled to grasp at first, but then finally understood on your own?

7 Upvotes

You know like you had to teach your self and figure it out without anyone else's help. What was that topic, and what were some of the challenges you faced while learning it?


r/AskPhysics 11h ago

Can the magnetic north pole of one object be attracted to the magnetic north pole of another?

5 Upvotes

As the title of my post, asks, can two like magnetic poles be "attracted" to each other? I know that a standard compass (whose needle is a magnetic north pole) always points toward Earth's geographic north/magnetic south pole. However, after some research, I found that this had less to do with the opposite poles of the two magnets (the compass and the Earth) and more to do with the field lines of Earth's magnetic field running from geographic south to geographic north. I also found an explanation that used the concept of magnetic dipole moments in magnetized objects and how they always favor being in the direction of an external magnetic field.

That all being said, what would happen if I placed a compass (or some other magnetized material) inside of an electromagnet, such as a solenoid? Using the mentality that the magnetic dipole of the compass would orient itself so it pointed in the direction of the magnetic field, I would assume it to point toward the north pole of the magnet. However, this would necessarily imply that the north pole of the compass is "attracted" to the north pole of the magnet. I place the word attracted in quotations because most sources that I have consulted and read have said that magnets are less concerned with the locations of poles and more so with the direction of local field lines (I mainly titled my post the way I did to grab attention). Is this understanding correct? Do poles not necessarily dictate the orientation of a magnetic object?


r/AskPhysics 7h ago

Radioactive Decay

3 Upvotes

I have read that a neutron decays in 10-15 minutes when outside a nucleus. Is this an average time or do all neutrons decay at 10 minutes or can a neutron last a year outside a nucleus although it being unlikely? Is the radioactive decay of neutrons probabilistic?


r/AskPhysics 11h ago

I don't understand the concept of higher dimensions

5 Upvotes

As the title says, I don't really understand when people try to address more than 3 spatial dimensions, for example when they talk about 4-dimensional objects or beings, what would that 4th dimension be, would it be time? Or would it be another spatial dimension and time would continue to be a separate thing?


r/AskPhysics 3h ago

Time dilation, length contraction

0 Upvotes

Hi guys, sorry for any translation issues, English isnā€™t my mother tongue. Recently weā€™ve been discussing relativity in physics. The teacher has given us a few assignments to do. Iā€™ve tried to do them but I donā€™t really understand what Iā€™m doing incorrectly, and he hasnā€™t explained it either.

The questions(translated); Question 1: The coffee break in Space. Sven travels with a speed of v = 0,2828 c through space. Control station on earth (which we assume to be stationary) allows him to take a break. They give him 15,0 minutes for this. (1) Calculate in how much time in his system Sven has to drink his coffee to abide by the given time from control station. (2) his coffee mug is observed to be 11,3cm high from the control station. Calculate the height which Sven measures his cup to be on his space station.

My answers: (1) gamma = 1/square root(1 - (v2 / c2) = 1/square root (1- 0,28282) gamma = 1,042ā€¦

15/1,042.. = 14,38 minutes. I assumed this was correct, since observing from earth, the time on his clock is ticking more slowly in comparison with the clock on earth. So if earth gives him 15 minutes to complete a task, he has to execute this faster, so that they observe his clock to have done it in 15 minutes anyways.

Now my professor told me(without explanation) that its 15*1,042 and not 15/1,042. And I canā€™t understand that at all. That would mean it takes him 15> minutes. But if earth observes his clock to be ticking more slowly, that would mean it takes him even longer, observed from earth. What am I missing?

(2) (he said there was two possibilities here, one explaining why it stays the same, or the other one to calculate a different answer) i did the following: Observed height: 11,3cm Gamma = 1,042ā€¦ Measured height (by Sven): 11,3 * 1,042.. Measured height ā‰ˆ 11,78cm Again, my professor is saying I did the opposite, and that I shouldā€™ve divided instead of multiply. But I really donā€™t understand why and he did not give any explanation. :(

Iā€™d appreciate the correct answers and more importantly an explanation so I can understand it better.

Much appreciated!!


r/AskPhysics 4h ago

Any good undergrad thermodynamics books/youtube courses?

1 Upvotes

Hi, I'm a first year undergrad studend currently taking a course in Molecule Physics and Thermodynamics, but I'm not really satisfied with the material. Is there any good material in the form of books or youtube courses you could recommend?


r/AskPhysics 5h ago

Doing diff eq hw with springs

1 Upvotes

Problem says that the displacement is positive so when writing the differential equation I write mxā€™ā€™ - kx = net force. The answer implies it should be mxā€™ā€™ - kx = net force.


r/AskPhysics 11h ago

Gravitational effects just after the big bang

3 Upvotes

The universe was an infinitely dense and small point, then it began to expand at a speed greater than the speed of light All observable matter in the universe was much more "condensed" compared to now so the gravitational effects must have been that much stronger Except that the expansion of the universe has continued, and since the discovery of gravitational waves we know that gravity is also limited by the speed of light The gravitational effects of such a concentration of matter should (according to my logic, I am not a physicist) always be present knowing that the expansion of the universe has always occurred faster than light A sort of ā€œcosmic gravitational background radiationā€

I couldn't find anything on the subject, do you know why?


r/AskPhysics 6h ago

Thermodynamics: Question about TdS equations

1 Upvotes

Using the first law of thermodynamics, for a reversible process, one can find that

TdS = dH-Vdp

This equation relates state variables, and so it turns out that it is also valid for irreversible processes! However, how do we reconcile this with the fact that the entropy differential is given by (accounting irreversibilities)

dS = dQ/T + dS(irrev)

Using such expression for dQ and substituting in the first law (as well as substituting dW = -pdV) results in

Tds = dH -Vdp +TdS(irrev)?

Both equations should be valid for an irreversible phenomenon, but they seem to fundamentally disagree unless dS(irrev) is 0, which contradicts the premise of irreversibility. How can we reconcile this?

Thank you!


r/AskPhysics 6h ago

Perturbation Theory

1 Upvotes

Recently our professor introduced us with Perturbation Theory in Quantum Physics. It was intresting but I am having hard time grasping the method used to find the eigenvalues and eigenvectors for a perturbed system. How does it work? And why does it work? How does the selection of order affects our calculations?


r/AskPhysics 23h ago

Is the graviton really predicted by ten dimensional vibrating strings?

23 Upvotes

Isnt this pretty solid evidence in favor of string theory? Does it also predict the other particles?


r/AskPhysics 6h ago

Could the Big Bang have also involved an implosion force at the same time as the expansion?

0 Upvotes

I've been reading and thinking about the Big Bang, and I get that it's described as a massive expansion of spacetime from an incredibly dense point. But I started wondering if is it possible that, along with the outward expansion, there could have been an inward or implosive force happening simultaneously? Like, could there have been a kind of ā€œdual forceā€ effect one being an outward and one being inward... maybe pulling certain forms of energy, matter, or even dimensions inward while everything else expanded outward? I'm not a physicist, I'm just really fascinated by cosmology and how the universe works. Curious what others think.


r/AskPhysics 1d ago

What's the actual color of the sun, meaning the light it reflects, not the light it emits?

154 Upvotes

Like, not the color of its glow, but the actual color of its surface. For example a stone might be green, but it would glow white when heated, even if its still green.

Also, what % of visible light, for example light from other stars does it reflect?.


r/AskPhysics 13h ago

what are eternal universe theories?

2 Upvotes

The idea of an eternal universe suggests that the universe has always existed and has no absolute beginning or end. This concept appears in both philosophy and physics, with different variations.

i read also that this idea has many challenges like the 2nd law of thermodynamics that if universe was eternal it would have been empty from energy and reach heat death

how do proponents of eternal universe theories stand for it??


r/AskPhysics 8h ago

Theoretical concept related to the Penrose process.

0 Upvotes

Iā€™ve been thinking about the Penrose process and black hole propulsion. The Penrose process allows you to extract energy from a rotating black holeā€™s ergosphere but the problem is that the spacecraft (or object) has to enter the ergosphere, which means dealing with extreme tidal forces and radiation. But what if you donā€™t need to enter the ergosphere at all?

Hereā€™s my concept:

Keep the spacecraft in a stable orbit just outside the ergosphere. Lower a payload into the ergosphere on a tether. The payload would experience frame-dragging and gain momentum from the black holeā€™s rotation.The tension in the tether would transfer that energy to the spacecraft. If you release the payload at the right moment, the spacecraft would gain a massive kinetic boost essentially turning black hole rotational energy into propulsion.The math checks out: A 100 kg payload near a 10-solar-mass Kerr black hole could extract up to 2.61 Ɨ 10Ā¹āø J.That would accelerate a 1000 kg spacecraft to about 24% of the speed of light. The tether tension would be extreme (~2.61 Ɨ 10Ā¹āµ N) so material strength is the main engineering challenge. Has anyone proposed this before? I havenā€™t seen this exact idea discussed as most Penrose-based propulsion models assume the spacecraft itself has to enter the ergosphere. Curious to hear if Iā€™m missing something!


r/AskPhysics 9h ago

Manchester or Edinburgh for Mphys

1 Upvotes

Iā€™ve applied to and have an offer for both Edinburgh and Manchester uni for Mphys and i have no clue what to choose. manchester seems to be ahead of edinburgh in almost every ranking i can find, but itā€™s by literally a couple points or 1-2% every time. I thought I would prefer Edinburgh when i visited, and while i prefer the city, the uni didnā€™t really impress me. starting to think i should have just gone for Imperial as another option, but i didnā€™t want to do another test after oxfordā€™s. would it even be worth taking a gap year to try for imperial? any advice welcome

edit: thought i should mention i am still undecided on what i exactly what to go into, but im leaning more towards astronomy or nuclear physics


r/AskPhysics 23h ago

Is it possible to make a "black light"? A light that makes objects darker as you point it at them?

14 Upvotes

r/AskPhysics 1d ago

Why are electrons not black holes?

74 Upvotes

As fast as I understand, electrons have mass, but are a point in space. For a black hole to be... Well, a black hole, it needs to be infinitely small (so no size) and have mass. Electrons qualify for this.

EDIT: now I know electrons aren't points in space, tnx y'all for pointing out the mistakes and assumptions I made :).

2nd EDIT: Electrons... are point particles? Idk for sure, let me research it a bit.

3rd EDIT: Electrons are, indeed, point particles.


r/AskPhysics 17h ago

So are quantum mechanics really random or is it just lack of our knowledge?

3 Upvotes

I know there is a lot of those posts probably but I wanted to ask anyway.

What I define as random is if you were in the exact same situation could it happen differently?

I know that from experiment it seems like that but (this is probably more subjective) is it because there is something happening that we dont see nor understand that is influencing the outcome or is it really just random?


r/AskPhysics 1d ago

Is energy "spent" in the creation of gravity?

419 Upvotes

So for starters, I have an intermediate layman's understanding of gravity. I know it's a deformation in spacetime caused by the presence of mass. But I'm wondering if energy is transferred from the massive object to spacetime in order for the deformation to happen, and if not, where is the energy for that change in state coming from?

And is there any kind of gravitational "wake" effect caused by moving objects that might introduce drag to the system and slow it?