Hole Definition and 1000 Threads

A hole is an opening in or through a particular medium, usually a solid body. Holes occur through natural and artificial processes, and may be useful for various purposes, or may represent a problem needing to be addressed in many fields of engineering. Depending on the material and the placement, a hole may be an indentation in a surface (such as a hole in the ground), or may pass completely through that surface (such as a hole created by a hole puncher in a piece of paper). In engineering, a hole may be blind or through if it is partial or complete depth.

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  1. J

    Laying a rope into a black hole very fast

    So, I lay a rope into a black hole, rope leaves the reel at velocity 0.99 c. When I observe the lower end of the rope, I never see it reaching the event horizon. Can I see some slack rope somewhere sometime?
  2. Sorthal

    Is time present in a black hole?

    Is there time inside of a black hole?
  3. M

    Finding the mass of a super-massive Black Hole?

    Hi, I am not too sure where to post this. I am studying for my astrophysics final and I came across this question which is pretty easy ( I think) but I can't seem to find the answer... S2 is observed to be one of the brightest stars orbiting the black hole at the center of Milky Way. It has...
  4. P

    What is the correct expression for tension in a chain falling through a hole?

    Homework Statement Pls help me with the (d) option of the question asked in the link https://www.physicsforums.com/showthread.php?t=724332&page=1 Correct expression for tension is ρgx/6 (as given in the answer sheet) Homework Equations The Attempt at a Solution...
  5. EinsteinKreuz

    Exploring Sagittarius A*: Supermassive Black Hole Evidence

    So I have a question about Sagittarius A*, which more and more astrophysicists are certain is a supermassive Black Hole. But now for the evidence part: 1. An alternative model for this object was proposed http://journalofcosmology.com/RobetsonLeiter.pdf published 4 years ago. So is there any...
  6. J

    Exploring the Mysteries of a Black Hole

    (Correct me if you think I'm wrong in anyway, I am open to new ideas.) A black hole is created when a planetary mass has its atoms completely cave in on its self. This creates a massive amount of gravity, one so massive that it even attracts photons (light). So does this mean that a black hole...
  7. U

    What is the Temperature of Vessel 2 After Effusion?

    Homework Statement Part (a): Explain what A and f means. Describe an experiment that shows this relation is true. Part (b):Find the temperature of vessel 1. Part (c): Why is temperature of vessel initially the same as vessel 1? Calculate the final temperature of vessel 2. Find the time taken...
  8. B

    How Do You Calculate the Flow Rate from a Rectangular Opening in a Tank?

    Homework Statement A rectangular opening is cut into the side of a large open-topped water tank. The opening has width W and height H2 - H1, where H1 is the distance from the top of the tank to the top of the opening, and H2 is the distance from the top of the tank to the bottom of the...
  9. V

    Hole current and Recombination

    Hello PFers! I hope everyone is doing well. Here's my question: The way I understand it (imperfectly, of course), forward-biasing a p-n junction diode, the electrons crossover from the n-type material and fall into the holes in the p-type material and then they are conducted through the holes...
  10. N

    How do I produce a hole with a square cross section?

    What are three different ways that i can produce a hole with a square cross section in a plate with a thickness of at least 1"?
  11. H

    Einsteins-Rosen bridge different from schwarzschild black hole metric?

    Hello, if you could help, I will be glad. I am studying the Einsteins-Rosen bridge (a matematically solution of the black hole) and I thought that the Einsteins-Rosen bridge was what we found making the Schwarzschild metric a change in kruskal coordinates. But reading an scientific article it...
  12. ShayanJ

    Metallic cube with circular hole

    There is a cube with its sides equal to d and its thikness equal to t. It also has a circular hole at its center with radius a (a<<d). Two sides of the cube are maintained at potentials V_0 and -V_0 . I want to find the potential inside the cube but I see no way for obtaining the boundary...
  13. S

    Black hole traveling near the speed of light

    Suppose a black hole travels at something like v = 0.999999999c relative to some observer. Does the black hole's event horizon becomes length contracted, thus appearing to turn into a black disk?
  14. V

    Surface gravity (Killing vecotrs) of Kerr black hole

    Hello, I am interested in surface gravity of Kerr black hole it means, I need to find killing vector for Kerr which is null on outer horizont. Is it true? How should I do that? I guess it could be some linear combination of vecotrs ∂/∂t and ∂/∂\phi. So can I looking for that this way...
  15. H

    Light & Black Hole: Absorbing Light w/o Mass

    Since light has no MASS... Then how does a black hole absorb light?
  16. michael879

    Black Hole via charge compression

    Here is my basic question: Lets say we have a massless charged shell with charge q and radius R. Is there some R where a black hole is formed? I haven't work this out with the EFE, but the calculations I've done are relativistic (GEM equations instead of EFE, for simplicity). I found that...
  17. C

    Does covering half of a hose affect the flow rate of water from an open tank?

    Let's say that you have an open tank of water and a hose connected to the bottom of it. Water is flowing out of the hose. You then cover half of the hose with your thumb. Will the flow rate (liters/second) right before you cover the hole be the same, less, or greater than right after you cover...
  18. A

    Objects falling into a black hole

    I have a question pertaining to objects falling through the event horizon of a black hole. It is my understanding that due to the immence gravity of a black hole and the way gravity affects the flow of time, that from the point of view of an observer at a safe distance from a black hole...
  19. mathworker

    MHB Johns Born Same Day: 24M Humans, 4 Letters

    Prove that least two humans named John should have born on same day(means with same D.O.B) if world has only 24 million humans and their alphabet chart contain just 4 letter 'J','H','O' and 'N' and there can't be more than one million humans of same name and world started just 2739 years ago...
  20. H

    Bolt hole fit and effect on shear capacity

    If I use the un-threaded section of a 3/8th inch bolt as a pin to lock a sprocket hub to a drive shaft I would drill and ream so that the bolt would need to be lightly tapped to go through the assembly. If the fit was looser (.025 thousands clearance) would that reduce the capacity of the...
  21. D

    Near black hole event horizon time dilation?

    Lets say we have a couple objects, one very close to a black hole, one a little farther out and then one a good distance away. Would the one very close to the black hole see the other ones time moving much quicker than their own time? How about just as they are going to hit the event horizon...
  22. A

    Can You See the Universe's Future from a Black Hole's Edge?

    Requested info for a sci-fi short story I'm writing: You are approaching the event horizon of a supermassive (10 billion Solar masses) Schwartzchild black hole in a magical spaceship which is capable of violating the laws of physics. You have not been free falling but lowering into the hole...
  23. L

    Does Spaghettification contradict space/time swap in a black hole

    Hi, I've heard and read that if someone was to fall towards a black hole, say feet first, they would undergo spaghettification at a certain distance, as the gravity at their feet would be much greater than the gravity at their head, and their body wouldn't be able to reisist the pulling effect...
  24. D H

    Superkick: Galaxy mergers can eject the central supermasive black hole

    Imagine a spinning skater. She pulls her arms in a little and spins faster. She brings her arms all the way into her chest, and spins really fast, and then bam! she rockets up into the sky. Seven years ago, computer simulations revealed a configuration of two spinning black holes that merged in...
  25. A

    Finding Center of Mass of Disc with Hole

    Homework Statement Find the center of mass of a uniform sheet in the form of a circular disc with a hole bounded by the equations x^2 + y^2 ≤ 1 and (x - 1/2)^2 + y^2 ≥ (1/16). Homework Equations The Attempt at a Solution
  26. J

    Light travelling towards a black hole

    I think I am wrong in what I am about to say so I someone could explain relatively simply where I went wrong I would be thankful... When light travels towards a black hole it's wavelength increases it's frequency and decreases it's wavelength due to the increase in energy. Because a black hole...
  27. Glurth

    FAQ-Is universe black hole: clarification request

    The FAQ states: "In our universe, we observe that space is not a vacuum, and tidal forces are nearly zero on cosmological distance scales (because the universe is homogeneous on these scales). " We observe Dark Energy. How do we know this accelerated recession of distant galaxies, which is...
  28. D

    Is there a density point which reduces anything to a black hole?

    First off I couldn't decide whether to enter my question in the relativity section or this one, so if I'm in the wrong place my apologies. Anyway I have a question or perhaps a hole in my understanding. I was wondering if there is a density point at which anything becomes a black hole. Now I...
  29. N

    Black Hole Formation and Iron Distribution

    Hi, does anyone know how much of the universes's iron or carbon has been made in supernovae that formed black holes? Is it 5, 10, 50 % of the iron currently pressent here? And, if se, do we have any idea how much of the average stars content gets traped in the BH versus the mass of the...
  30. S

    Help Understanding Black Hole Theories

    Hi, I think I have several misconceptions about the theoretical framework of black holes, I'm just not sure where my intuition (or, lack of) goes wrong. So sorry if this sounds really stupid, any help is appreciated. The scenario that I find confusing is what Alice sees when she throws Bob into...
  31. J

    Black Hole Firewall: Exploring the Limits of Energy and Entropy

    I was thinking about how a black hole evaporates and the firewall idea. If after Page time a firewall forms around the black hole, does that mean that the energy/mass, and entropy cannot increase anymore? The energy of the black hole is essentially supposed to be in the singularity, right? I...
  32. D

    Spin of Black Hole Directly Measured?

    I thought this was cool, wasn't able to find a paper on it, but didn't look "super hard", and won't pay for it. Apparently, a gravitational lensing has lined up so perfectly that we were able to measure the black hole's spin. They have it at "half the speed of light" (??!)...
  33. J

    Could universe be a blackhole inside a white hole?

    Would it be possible for the universe to exist as a white hole within a black hole? I know about the whole black hole universe theory, though I never really looked into it.
  34. S

    Relativity and Black Hole Question

    Assume that there exist two people, person A and person B. Person B is falling into a black hole. I understand that due to relativity and time dilation, person A will have to spend an infinite amount of time to watch person B cross the event horizon. Person B will appear to move at a slower...
  35. tom.stoer

    Black hole collapse - ray tracing

    I know several raytraycing results for static Schwarzschild black holes, but I have never seen something similar for collapse models like Oppenheimer-Snyder or Vaidya. Are there reliable raytraycing results showing the effect on light rays from far distant light emitters observed by (far...
  36. Philosophaie

    Is energy and mass extraction possible within the Kerr Black Hole Ergosphere?

    In a Kerr Black Hole there exists a region called the Ergosphere. It is between the Event Horizon and a spheriod called the Static Limit. The Event Horizon can be simplified to: ##\Delta## = 0. The Static Limit can be simplified to: ##g_{tt}## = 0. They yield two separate spheres...
  37. Philosophaie

    Angular Momentum of Kerr Black Hole

    Homework Statement How do you find the Angular Momentum, J, if you are given the Angular Velocity, ω of a Kerr Black Hole. Homework Equations J = I*ω ##I = mass*r^2## Event Horizon: ##r_+ = M + (M^2 − (J/mass/c)^2)^{1/2}## Static Limit and the Ergosphere: ##r_0 = M + (M^2 −...
  38. O

    Black Hole Information Paradox and Alcubierre Warp Drives

    Suppose Alcubierre warp drives or some alternative form of warp drive is possible. Then surely a warp drive could enter the event horizon of a black hole, observe the interior, and exit the horizon, returning with information from within the black hole. What about black holes never visited by a...
  39. Y

    Fuel conservation near a Schwarzschild black hole

    In another thread we determined that the proper total force acting on an orbiting object in the Schwarzschild metric, is given by: ##f_{total} = \frac{Mm}{r^2\sqrt{1-2M/r}} - \frac{mv^2}{r}\left(\frac{1-3M/r}{(1 - v^2)\sqrt{1-M/r}}\right)## One interesting aspect of the equation is that when...
  40. H

    If light approaches a black hole will it accelerate?

    If light approaches a black hole will it accelerate? I think this question ties in with whether light has mass or not. Does light have mass? It seems accepted that light has momentum, but this is not consistent with saying that photons are mass-less (momentum=mass*volume). Could someone clear...
  41. F

    Black hole similar to pre universe

    Hey all, I was wondering if the singularity at the bottom of a black hole is similar to what the universe would be like before the big bang, i.e. heaps of mass/energy concentrated into a tiny point. To me I always think of black holes as sinkholes dotted throughout the universe which are...
  42. PsychonautQQ

    Power radiated through a hole in small wavelength distribution

    Homework Statement A cavity at Temperature 6000k has an energy distribution corresponding to a blackbody. We make a small hole in it 1mm in diameter. Calculate the power radiated through the hole of wavelength interval between 550nm and 551nm. HINT: when dλ is small (such in this case)...
  43. G

    Black hole information paradox?

    Would it be possible for a black hole to carve a trail of information on two dimensional space in the holographic universe? Could the black hole, acting as a conduit between the macro and micro universe, due to its properties at the singularity (at the plank scale) carve the the information...
  44. C

    Redshifting Through Hole in Earth

    I have been wondering what to expect if there was a hole, from pole to pole, that inside which we could measure the Einstein red and blue shifts due to gravity. At first, I suspect a blue-shift as light travels from the surface of the Earth to the center; just less and less as the center is...
  45. dheeraj

    Difference between micro black hole and primordial black hole

    If the amount of hidden information inside a black hole, depends on the size of the hole, one would expect from general principles, that the black hole would have a temperature, and would glow like a piece of hot metal. But that was impossible, because as everyone knew, nothing could get out of...
  46. N

    Heating a steel plate with a hole in it

    Homework Statement If a steel plate with a hole of 10 cm in diameter is heated 35 degrees kelvin, what will the new diameter be? ##\alpha_L = 13 \cdot 10^{−6} K^{−1}##Homework Equations ##\Delta L = \alpha_L \cdot \Delta T \cdot L## The Attempt at a Solution If I understand the...
  47. I

    Turbine engine burner can hole size

    Im building a turbine engine and I am having trouble figuring out the hole sizes for the burner can, my problem is that I am not using a compressor section but rather using an air compressor for the air intake so I can't use the standard formula, can I? If I know my blad diameter and the flow...
  48. Nugso

    Speed of Swallow of a Black Hole

    Hello everyone. As far as I know, even lights can not escape from black hole once the light reaches to even horizon as lights carry momentum hence energy. Now, what I wonder is, how fast do black holes swallow light or, if you will, other objects? I guess it cannot be faster than the speed of...
  49. S

    Flow of electrons hit a potential hole

    Homework Statement Flow of 500 electrons per second with kinetic energy 3 eV hits a perpendicular 5 eV potential hole 0.3 nm wide. How many electrons pass per second pass the obstacle? Homework Equations The Attempt at a Solution Hmm, I checked my notes where it is written that...
  50. U

    Effusion of molecules into a Box through a hole

    Homework Statement A container of volume 10−3 m3 has a pressure of 10−7 mbar. Surrounded by air at 1 bar and 290 K, how long does it take the pressure inside to rise to 10−6 mbar when air effuses through a small hole of area 10−17 m2? Homework Equations The Attempt at a Solution Flux ø =...
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