What is Hole: Definition and 1000 Discussions

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. 9

    Can a threaded tapped joint function as a friction joint?

    I have a tapped hole. A threaded rod goes through the hole. A single nut secures the threaded rod in position. Only one plate is threaded. Note the clearance hole in the top plate. A picture is attached. A friction joint in a bolt occurs when the clamping force creates a normal force. This...
  2. B

    Maximum angular momentum for charged black hole?

    Hi all I gather a normal black hole has maximum angular velocity at the point that the event horizon is moving at The speed of light. However what would be the maximum rotational velocity for a maximally charged black hole- for example one made purely of electrons? Thanks
  3. J

    Help calculating The mass of a Black hole (homework help)

    on this lab worksheet i need to fill out the bottom table (the top one is already filled out). I am having trouble understanding The numbers in the first part of the chart. I know RA is right accession and DEC is declination but what I'm not understanding is why there are two different numbers...
  4. E

    Max Height of Water in a Container with 0.1mm Hole: Solving h

    Homework Statement A container has a round hole at the bottom. The diameter of the hole is 0.1 mm. The container is filled with water. The maximum height (in m) up to which whiter can be filled without leakage is h/10. Find h. Surface tension= 75 * 10^-3 N/m Homework Equations Pgh*A=F(of...
  5. Uberhulk

    Which Has A Stronger Gravitational Pull - A Black Hole or Neutron Star?

    Is this established or is it dependent on the size of the black hole? http://www.space.com/22180-neutron-stars.html Neutron stars pack their mass inside a 20-kilometer (12.4 miles) diameter. They are so dense that a single teaspoon would weigh a billion tons — assuming you somehow managed to...
  6. avito009

    If the sun becomes a black hole will its schwarzschild radius change?

    I know that the schwarzschild radius is proportional to the mass. But in case of black holes the mass remains the same only the size and density changes. So does the schwarzschild radius stay same when it is the sun and when it becomes a black hole?
  7. wolram

    Can black holes hold the key to the origin of our universe?

    arXiv:1410.3881 (cross-list from gr-qc) [pdf, ps, other] Universe in a black hole with spin and torsion Nikodem J. Poplawski Comments: 10 pages Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics - Theory (hep-th)...
  8. StonedPhysicist

    Origin of our universe 4D black hole

    The brains at the Perimeter Institute recently published a paper describing how our 3 dimensional universe could possibly exist as the event horizon of a 4 dimensional black hole in a 4 dimensional universe as the event horizons of black holes have one less dimension than the black hole itself...
  9. S

    Have theories been formed yet on how to stop a black hole?

    Have theories been formed yet on how to stop a black hole?
  10. T

    Can I Prevent Black Hole Formation?

    If I were to travel towards a BH at, once again, close to c -- would I, in my frame of reference, prevent (observationally at least) the formation of a BH? In other words, can I match my speed with that of the collapsing object's light or even infalling matter (in an already formed BH) from...
  11. Sandhani Boruah

    Is a Connection Between Black Holes and Time Machines Possible?

    can a black hole be connected with the making of a time machine ?
  12. stevendaryl

    Growing Black Hole Metric Approximation: 2MG/c^2

    This is a question inspired by the "Golf Ball" thread, which is no longer open for comments, I guess. For a black hole of constant mass, the metric external to the black hole can be written in Schwarzschild metric, which is characterized by the constant M, and the corresponding radius 2 M...
  13. rjbeery

    Black hole formation with golf balls in GR

    Start with an existing black hole and an event horizon radius R at time T. Say the black hole is being "fed" an infinite series of golf balls, one after the other, which are all stamped numerically such that the current golf ball external to the event horizon is 1.0 * 10^32. See linked img...
  14. F

    Orbits around a Schwarzschild/Kerr black hole

    Hi everybody, Around a black hole, a test particle can experience two types precession: of its pericenter and of its angular momentum vector. I would like to know if there exist an EXACT expression for the rate at which these two precession occurs both for a Schwarzschild and a Kerr black hole...
  15. avito009

    Who should we give credit for considering the possibility of Black Hole?

    General Relativity predicted existence of Black holes. The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole. But The Chandrasekhar limit is the maximum mass of a stable white dwarf star. White dwarfs with masses greater than the...
  16. avito009

    Calculation of gravity near a black hole.

    Newtons Universal law of gravity equations are an excellent approximation when dealing with low velocities (i.e., velocities whose magnitude is much smaller than the speed of light) and when dealing with weak gravity fields (such as those found on Earth or around low-mass stars). The...
  17. avito009

    Gravity of Black hole far away.

    Why the gravity around a black hole remains normal unless you get extremely close? But first: How far from Earth is there zero gravity? Gravity declines as a function of the square of the distance from a mass. Earth's gravity is less and less as one goes further away, but is never zero. A...
  18. G

    Thanks for any thoughts,Could Black Holes Pump Energy into the Quantum Foam?

    Hello Everyone, This is my first post, I hope I've picked the right forum for this question. Could a black hole be "pumping" space/time/matter back into the quantum foam? I guess this is asking could it compress whatever falls into it down past Plancks constant?
  19. M

    What Happens at the Center of a Black Hole?

    i was bored and my mind wandered. a question popped up and it got me interested in what others thought who are more informed than me: since black hole is a theoretical construct (and hence can be geometrically perfect), what happens at the exact center of it. with uniform (assumed) density...
  20. PeterDonis

    "Centrifugal Force Reversal" Near a Black Hole

    [Reposted from my PF Blog.] I haven't yet had the pleasure of participating in a PF thread on this topic :wink:, although I have made at least one post that refers to it in passing. But I know there have been some in the past, such as this, so I wanted to post a quick treatment of the topic...
  21. J

    Is a black hole black from all directions?

    Black holes are usually shown as funnels. Is there one "funnel" pointing in a single direction or are there event horizons and "funnels" seen from every direction?
  22. K

    As I Was Looking At A Strange Black Hole Image I Wondered

    Hey! I'm new here and I just wanted to ask a question and maybe I'll come back here once I have started college in a week or so. :P But firstly I must say, at first I thought the confirmation question for signing up was a science question about acid and I was totally stumped. But that's PH... I...
  23. T

    Our universe may have emerged from a black hole in a higher-dimensiona

    An interesting article for ordinary people but I just wondered if it is science or pseudo science? It offers an explanation why the Universe has a beginning and has finite age. To me it suggests many Universes occurring at random, like raindrops falling randomly into an ocean of space time...
  24. J

    White Hole Theory: Evidence in Our Universe

    Recent data in qm suggest black holes could decompress into a white hole on either our universe or another as such is there any evidence of white holes in our universeSent from my iPhone using Physics Forums Jim P
  25. D

    Is the Answer Correct? Dipping a Cylinder w/ Small Hole in Liquid

    An empty cylindrical vessel with a small circular hole of radius r at the bottom is dipped vertically in a liquid of density d keeping the bottom downward. At what maximum depth can it be dipped before the liquid enters into it? The surface tension of the liquid is S. The answer given in the...
  26. D

    Do we live in a black hole(or an white hole)

    i had this science project in school on black holes and i came an article stating we live in a black hole theory link -----> http://www.technologyreview.com/view/419827/why-our-universe-must-have-been-born-inside-a-black-hole/ so i was thinking that if our universe is made up inside a black...
  27. B

    Does mass dissipate in a black hole?

    Thinking about how so much matter can be squeezed into a singularity, the answer (if I understand correctly) is that the matter just stacks upon itself down an infinitely long weird space-time well. In a sense, the last item in masks the ones below. But doesn't this impact the gravitational...
  28. B

    DTQE idler photons fall into a Black Hole- interference at d0?

    Experiment: Imagine the dalayed time quantum eraser experiment, except the pair of "idler" photons(which would normally pass onto the detectors d1,d2,d3,d4) instead fall into a black hole. Would d0 detect interference or not? It seems commonly accepted that the information of...
  29. O

    Are There Exact Black Hole Solutions in Non-Asymptotically Flat Spacetimes?

    Are there any EXACT solutions similar to Schwarzschild or Kerr in a spacetime which is not asymptotically flat; e.g. FLRW or other cosmological metrics? I am already familiar with the "Swiss cheese" approximations.
  30. PhizKid

    Pendulum pulled through hole adiabatically

    Homework Statement A string with a lead ball of mass ##m## is slowly pulled upward through a small hole. Consider the work done on the system during this process and find the change in energy and the frequency of this pendulum during this "adiabatic process", assuming the amplitude of the...
  31. C

    What happens if there is no singularity inside a black hole?

    Hello. I'm a layperson curious about physics. I've read that Quantum Gravity could eliminate the predicted singularity inside a black hole based on General Relativity. If that's true, what would happen from the frame of reference at the center of a black hole? Would that cause a tremendous...
  32. K

    Finding Equilibrium: Solving a Black Hole Parking Problem

    Consider two black holes: the left one has a mass M1= 5x10^30 kg, and the right one has a mass of M2= 9x10^30 kg, and they are a distance d= 3.0x10^6 m apart. A spaceship passing between them is having engine trouble and so the captain has to park the ship somewhere where he won't get sucked...
  33. RabbitWho

    Poking someone falling into a black hole with a stick

    Please excuse me for being a complete and utter pleb, my meager knowledge of Leonard Susskind's holographic principle comes from the second episode of the documentary "Through the Wormhole" (which is available online but I won't link to in case it is copyright infringement?). He talks about...
  34. Ookke

    Momentum transfer when object falls into black hole

    Let's imagine a stationary black hole and a fast moving object falling into BH. Let the momentum of the falling object be enough to give an observable bump to BH, pushing it into motion. Since the object does fall into BH, by momentum preservation BH should start moving. But I don't see how...
  35. A

    Solving an Energy Problem: Calculating Average Molecule Energy Through a Hole

    Hello everyone. I was hoping someone could help me out with the following problem. I tried working it out, but I don't know if I did it correctly or if I missed an important point. It just seems too "short". it would be much appreciated if someone could go through my solution quickly and give...
  36. B

    How Do Equations Demonstrate Time Dilation Near Black Holes?

    What are the equations that shows that time slows down as you near a black hole? I'm trying to prove to a non-believer that the math is there and shows this. Thanks!
  37. julcab12

    Black hole fireworks: quantum-gravity effects outside the horizon spar

    http://arxiv.org/abs/1407.0989 White hole anyone?..^^ "...intense gravity creates a horizon, but it is not an event horizon. It is locally like an horizon, but not globally. So, matter is trapped for a while, but not forever; it is called sometimes a “trapping” horizon."-CR
  38. S

    Exploring the Stability of Black Holes: Can They Be Broken Apart?

    dear sir, i am curious to know whether black hole can be broken apart by some means?
  39. R

    Is Dark Energy Actually the Pull of Black Holes?

    Instead of being a force that works against gravity. Is it possible that dark energy is the pulling of everything towards the event horizon of a black hole? This would marry dark energy with gravity and replace myserious massive amount of energy with a logical source of energy/force that we know...
  40. M

    The black Hole Wars - Losing Information in the Hawking Radiation

    So as I understand it, Hawking theorized that due to the behaviour of virtual particles on the event horizon of a black hole, eventually the black hole would "evaporate" through what was coined the Hawking Radiation. But what I'm curious about is Hawking's interpretation of the event in that...
  41. A

    Speed of a mass near black hole

    By theoretical calculations of super dense black holes show their gravity exceeding to a limit that can pull in light into the heavenly body. This means that the gravitational pull, which are actually acceleration as shown by the Relativity theory, is greater than the speed of light. So won't a...
  42. S

    Can black holes merge to create larger event horizons?

    Hi! New here. Be gentle. Kinda an idea that popped into my head a little while ago: Are the tidal forces of some black holes powerful enough to separate quark groups? Google seems to be a bit iffy on the subject.
  43. Nova

    Does a Black Hole grow in mass?

    It is confirmed that Black Holes have variations of masses. But these masses are said to be gained from the base mass from the Supernova it's born from. Another way a Black hole gained mass was that the collisions of multiple Black Holes caused it to add on to the mass of each other, such as...
  44. R

    Why does A black hole need a massive center

    Was thinking about this why is it a requirement that the center of a black hole be a singularity? If the event horizon contained all the mass of a black hole would it still not have the same effect on it's surroundings? Why could it not be similar to a a crystal where as each molecular link or...
  45. HeavyMetal

    Electrostatic attraction between an electron and a hole

    The exciton is defined as a bound state of an electron and an electron hole. From what I've read, this state is described by Coulomb's law. Coulomb's law describes the interaction between two charged particles. So my question is: because an electron hole is not an actual particle, how does an...
  46. A

    Sound energy passing through a hole

    Homework Statement "A continuous sound wave with a sound intensity level of 80dB passes through a hole in a wall which has a cross-sectional area of 3m^2. How much energy passes through this hole in 10 minutes, in joules?" If anyone can show me how this problem is solved it's be much...
  47. F

    E-field in a cylinder with a hole parallel to its axis

    Homework Statement A long insulating cylinder of radius R1 has a cylindrical hole parallel to the axis of the cylinder. The radius of the hole is R2, and the distance from the centre of the cylinder to the centre of the hole is a. There is a uniform fixed charge per unit volume ρ throughout...
  48. 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?
  49. Sorthal

    Is time present in a black hole?

    Is there time inside of a black hole?
  50. 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...
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