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. A

    Black hole accretion: angular momentum loss

    Why exactly is it necessary for angular momentum to be lost by a mass if it is to accrete around a black hole? the mass is decreasing its radius, so it speeds up: thus angular mometum is conserved. But everywhere it is saying that 99.99% of the angular momentum must be shed for accretion to...
  2. S

    Time for a Droplet of Water to Fall .25m from Hole

    Time for Droplet of Water to Fall .25m from Hole Homework Statement A cylindrical tank .7m tall is filled with water and placed on a stand (below it) that is .3m tall. A hole of radius .001 m in the bottom of tank is opened. Water then flows through the hole and through an opening in...
  3. S

    Black Hole Angular Velocity: Is Expansion Feasible?

    Could a small black hole achieve an angular velocity such that the centripetal force is >= gravity, which would expand it enough to turn into a quark star or neutron star? I realize that in order to rotate the black hole further, more mass must be added that will increase the amount of...
  4. A

    Black Hole Radiation: Stephen Hawking's Theory Explained

    Hi, According to Stephen Hawking, it is theoretically possible for black holes to emit radiation. How is this so? As I understand, please correct me if I'm wrong, it has to do with the creation of particle/antiparticle pairs. Are these particles generated as a result of the intense...
  5. F

    What events occur inside a black hole?

    As we know, the gravitational pull of the black hole is too strong, not even light can escape from it... Let me assume 2 person: A and B A is sucked into a black hole while B is outside the event horizon... At first, B will notice that A has disappeared due to the lights(image) of A is...
  6. C

    Center of mass of a disc with a hole

    there is a similar case here :https://www.physicsforums.com/showthread.php?t=296966 so I've tried it and what i did was to equate both individual moment of inertia about z axis (and later applied parallel axis theorm) with negative mass for hole. added both these and found out Ix = M/4...
  7. M

    View of universe from event horizon of black hole

    If I flew over to a the nearest black hole with the Hubble scope on a trailer (cough), how would the performance of the scope differ from current, particularly with regards to observing extremely distant objects. In particular, when time dilation becomes extreme as my orbit of the BH nears...
  8. P

    A couple of interesting black hole papers

    In another thread (on Oppenheimer-Snyder collapse), I posted a link to some lecture notes on gravitational collapse. Checking on the author, I find he is extremely prolific on many fundamental areas of GR (from the computational standpoint). Of particular interest...
  9. A

    Electron falls into black hole. what happens.

    the electron falls and emits radiation. will it lose all it's energy by the time it reaches the event horizon or will it have enough (>2m) to produce a particle shower? Will other things happen?
  10. P

    Black hole mass as function proper time

    Hi there. 1. The problem statement I am asked to write the equations which give us the mass of a black hole as function the proper time. Homework Equations The Schwarzschild metrics is given by $$ ds^2=-(1- \frac{2GM}{r})dt^2+(1-\frac{2GM}{r})^{-1}dr^2+ r^2(d\theta^2+ \sin^2(\theta)...
  11. LarryS

    How To COUNT Information in Black Hole?

    I have not read any formal (mathematical) explanations of black hole thermodynamics, only popular literature on that subject. I have read that the total amount of information, and therefore its entropy, that a black hole can contain is proportional to the area of its event horizon (measured...
  12. U

    Circular Plate with eccentric hole

    Hi everybody, I'm looking for a way to determine the maximum moment of a uniformly loaded circular plate (diameter = 10") with eccentric circular hole (diameter = 4"). The plate is clamped at outer edge and free at inner edge. The ultimate objectif is to determine the minimum thickness of...
  13. J

    How close could a tachyon get to a black hole and still escape?

    How close could a tachyon get to a black hole and still escape?
  14. E

    Rational function hole at (0, 0)?

    The function is f(x) = 2x / x3 - 6x2 + 3x + 10 I was taught that any rational function with a numerator of smaller degree than the denominator has a horizontal asymptote at y = 0, which would apply in this case. This makes sense for the end behaviors because as x approaches +/- ∞, y...
  15. O

    Why is BOTH the electron & hole drift velocity positive?

    Good Morning, The equations under investigation: Electrons: J = enμE + eD(dn/dx) Holes: J = epμE - eD(dp/dx) n or p = concentration of electrons or holes respectively D = diffusion constant μ = mobility The question in mind is as follows: If holes are...
  16. G

    Why do functions have holes and asymptotes?

    I don't understand why there is a hole in the graph of a function when there is a non-zero number in the numerator of a function and zero in the denominator, but an asymptote when both the numerator and the denominator are zeroes. Can someone explain why this is the case?
  17. Vorde

    What Is a Black Hole Firewall?

    Hello all, Cosmic Variance just had a great post up about Black Holes, wherein they were talking about something called the firewall, located at the horizon. I gathered it was a result of the Unruh Effect + Hawking Radiation, and CV seemed to say that this would cause anyone passing the...
  18. S

    Black hole has a partiuclar fixed volume

    for example take two halves of a black hole as m1 and m2. since we told black hole has no volume so we take distance between the two halves as 0. by Newtons laws of gravitation the force of gravitation between the halves is infinite. that is the black hole can shrink the universe to a...
  19. C

    Black hole drive in the film Event Horizon

    Black hole drive in the film "Event Horizon" Cheesy movie, right? A lot of fun though. For those who don't know, there is a starship in the film called the Event Horizon, which utilizes an artificial black hole drive/engine in order to allow it to fold space, although it's probably more...
  20. L

    Black hole temperature derived from entropy (heat from black hole?)

    Hey, The entropy of a black hole is S = kB (4∏GM2)/(hbar c) S=Q/T T= Q/S T = Q (hbar c)/ (4∏GM2kB) The temperature derived from hawking radiation is: T = c3 hbar/ (8 pi G M kB) Which implies Q = (1/2)M c2 Is this true? I have found online that the heat should equal...
  21. L

    What is the Correct Q for Calculating Black Hole Temperature?

    hey guys, i'm working on this question to approximate the entropy of a black hole, the approximation is that for the maximum entropy to be obtained you need a maximum number of particles to create the black hole, the particles must have low energies - large wavelength photons, but the...
  22. S

    Exploring the Possibility of an Antimatter Black Hole | Scientific Inquiry

    okay, this might be a very silly question but whatever. If a black hole were composed of antimatter, would we be able to tell? If the black hole were created by anti-matter collapsing and becoming dense enough to turn it into a black hole, then if regular matter fell into it, it wouldn't...
  23. B

    Drilled hole through earth - Diff EQ w/ Gauss' Law

    Homework Statement Suppose that a hole has been drilled through the center of the earth, and that an object is droppped into this hole. Write a first order linear differential equaiton for the object's velocity, v as a function of the distance r from the Earth's center (i.e, and equation...
  24. W

    3-dimensional implications of a black hole

    I am loving this forum :) I am troubled by the conventional image of space being inverted by a black hole - if that's the correct way to phrase it. But I'd like to take a step back and use a model to explain. We observe an enclosed room, shaped like a cube, with 1,000 cubic feet of space...
  25. E

    Exploring BTZ Black Hole & Geodesics

    Hi everybody. I am well aware that there is only one black hole in 2+1, i.e., the BTZ one. I also know that for vanishing and positive cosmological constants we get solutions with a conical singularity. My question is more about the interpretation of these last results. Assume that in the BTZ...
  26. A

    How Do Black Holes Emit Photons?

    Hi, I've been reading through Stephen Hawking's 'A Brief History of Time' and I have reached a section about how, contrary to popular belief, Black Hole's are not necessarily black since they emit photons outside the event horizon. I am wondering how they emit photons. Does it have to do...
  27. 9

    Exploring the Mysteries of Black Holes: Comparing the Phenomenon to a Lit Fire

    This may sound very silly and a tad bit hard for me to explain, but here goes! I have experienced and seen how when a lit fire was covered with a container, the oxygen begins to dissipate and it begins to suck things into the space. (I did not light myself on fire!) So I was wondering if...
  28. X

    Black hole and angular momentum

    It's theorized that most black holes have rotational speed. Also, I'm guessing, event horizons are always spherical or close to spherical because they are a function of the gravity well extending from center mass of the black hole. My question is this, could a black hole ever rotate with such...
  29. C

    The God Effect and the Black Hole

    Friends, Acquaintances, and Juvenile Delinquents alike lend me your ears... As a thought experiment, let us say we have two photons, photon A and photon B. Now our two lovely quanta of electromagnetic radiation are special, because they have been entangled after an atomic cascade. After the...
  30. A

    Can We Pull a Metal Ball Out of a Black Hole With a Steel Cable?

    There is a spaceship situated orbitting a black hole at x million miles. We have an exactly x milllion mile long string (perhaps a bit longer) Lets not call it a string, but a flexible steel cable instead. Now, we tie a metal ball at its one end, and project the ball towards the black hole...
  31. J

    Math Olympiad problem - Applying induction and the pigeon hole principle

    Ok, so this problem looks like an induction problem to me, so I used that, but I only got as far as the induction hypothesis. The hint says to use the pigeon hole principle. I'm not sure how to use that for this problem.
  32. K

    What would happen if someone was sucked into a black hole?

    Hypothetically, what would happen if a person was sucked into a black hole? Would they just simply die?
  33. bcrowell

    Review article on astrophysical collapse to a black hole?

    Does anyone know of a review article on astrophysical collapse to a black hole? There are several statements I've picked up from WP that either surprise me or that I'm not sure I understand. This Penrose diagram http://en.wikipedia.org/wiki/File:PENROSE2.PNG shows the singularity as being...
  34. bcrowell

    Define Black Holes w/o Asymptotic Flatness?

    I see statements that in order to define a black hole, we need asymptotic flatness, but this only seems to be necessary because we want to define the horizon as the boundary of a region from which light can't escape to null infinity (\mathscr{I}^+). It seems like you can have a well defined null...
  35. tworitdash

    Exploring the Mass of a Hole: Propagation in Semiconductors

    How can the mass of a hole is larger than an electron?I want to know what a hole signifies and the mass energy required for it to propagate in the semiconductors for constituting current.
  36. A

    Black Hole Time Dilation: Light-ray Interpretation

    I know that a black hole creates infinite curvature in spacetime and hence infinite time dilation. I was wondering though, if I could think of this stopping of time due to the fact that a light ray moving radially towards the centre of a black hole would have to travel infinitely far along the...
  37. N

    Hawking Radiation inside a Black Hole?

    I've seen it said somewhere that an observer falling into a black hole doesn't notice anything qualitatively unique at the exact moment they cross the event horizon. Does this include Hawking radiation? That radiation is described as being emitted by the event horizon, so once the observer...
  38. K

    Wire through a hole - diameter question

    I'm trying to find a silver chain that can be used for a small bead with a small hole. Obviously, the chain needs to be thin enough to fit through the hole, but I can't measure the hole inside the bead by hand. I found a chain that is 0.9mm in diameter, but I'm not sure the bead will fit. So...
  39. S

    Mass Absorption -V- Black Hole size

    How much mass would even the smallest of black holes have to absorb (keeping also in mind the radiation lost as it grows) to obtain its size? And considering the largest Black holes discovered so far, how much mass would it have had to gobble up to get to that size? On the average, how much...
  40. Pruddy

    Dropping a mass in a hole through the Center of Earth

    Homework Statement Assume that the Earth is a uniform density spherical mass. (This assumption is not correct but we will use it for simplicity in working the problem.) The deepest hole drilled into the Earth's surface went to a depth of 40,230 ft (Wikipedia.org). Imagine that this hole was...
  41. D

    Null geodesics of a Kerr black hole

    Homework Statement Hi, From the Kerr metric, in geometrized units, \left(1 - \frac{2M}{r}\right) \left(\frac{dt}{d\lambda}\right)^2 + \frac{4Ma}{r} \frac{dt}{d\lambda}\frac{d\phi}{d\lambda} - \frac{r^2}{\Delta} \left(\frac{dr}{d\lambda}\right)^2 - R_a^2...
  42. F

    Eternal black hole Hawking process

    Hi all, I am trying to understand the process of Hawking radiation in the case of an eternal (static/everlasting) black hole. As a bit of background: i understand (semi-quantitatively) how one gets particles produced when one is a frame with constant acceleration. And I sort of understand...
  43. A

    HELP Investigating the rate of discharge of water from a hole in a bucket

    Hey guys, um I'm currently in grd 11, and for my physics assignment, I've chosen to investigate the flow rate of water from a leaky bucket. It is relatively simply however, I've been trying to find a suitable formula/s to equate the flow rate at different heights, ie, the volume of water over...
  44. H

    Can the Holographic Principle Solve the Mystery of Black Hole Information Loss?

    I am trying to get my head round this problem but not having studied it I need some help.
  45. B

    Too fast for a black hole to consume?

    I read an article yesterday about the fastest moving pulsar yet detected. The Chandra X-ray observatory spied a pulsar in SNR MSH 11-61A and IGR J11014-6103 moving at approximately 6 million miles an hour. This raised the question in my mind of what would happen if this pulsar were to collide...
  46. Y

    What is the conventional over drill size for a 0.05 pin on a PCB?

    I am laying out pcb and I want to confirm about the over drill size for a pin. The pin is 0.05". I forgot what is the conventional over size drill. Is it 0.06"? Or 0.065 to be safe? Thanks Alan
  47. A

    Spatial dimensions inside a black hole

    hello all I am so glad to have found this forum. I've always had an interest in astrophysics, cosmology, SR/GR, etc, and no place to ask questions. I'm an engineer and was once a member of Mensa (I only left the organization because I thought other members were crazy. Sorry). So although I'm...
  48. mrspeedybob

    Can a Photon Create a Black Hole in Different Frames of Reference?

    I know that in scenarios where QM and GR are both applicable the answerers come out ridiculous. I believe this may be one of those scenarios. It is also possible that I have some misunderstanding that leads to a ridiculous answer. My question is which of these is the case. A photon is...
  49. I

    Black hole - frequencies used for viewing

    Hey, In space missions why do they choose different frequencies for viewing stars? For example why do they choose both 43 GHz and 230 GHz to view a black hole? Cheers!
  50. 0

    Pulling information out of a black hole

    Can somebody help me out here. The gravity of a black hole is so strong that nothing can escape it, not even light. If that's the case, why can't another black hole of larger mass be used to extract information from the first black hole? Sort of like how a Siphon works. I imagine some sort...
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