What is Holes: 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.

View More On Wikipedia.org
Recent contents Top users
  1. X

    Exploring the Interaction Between Photon Energy and Black Holes

    First, a question. I assume that a photon can be captured into a stable orbit around a black hole. It seems it would just be a function of the radius of the event horizon and the velocity of the photon (always c I know but the vector is the important part). Where would this stable orbit be in...
  2. J

    Comparing Large Stars and Black Holes: Understanding Event Horizons

    A comparison of a large star and a black hole: Both have identical masses. Correct me if I'm wrong but gravitationally, they would be the same because we assume that the gravitational force acts from the center of mass. So here's the question: If both the black hole and the star have the...
  3. Crazymechanic

    Unraveling the Mystery of Black Holes: The Paradox of Singularity and Infinity

    Scientists say that in mathematical terms in singularity all the math breaks down and you get infinity. But how come this be if the black hole formed from a star that had huge but still limited amount of matter/fuel in it, and that limited amount just got highly compressed. And if there even is...
  4. S

    Straight Pipe with many holes air consumption?

    I need a formula! Please help! Imagine a 9' long 1"IDx1.25"OD pipe. Along the length of this pipe there are a couple hundred ∅1/16 holes. If I'm feeding 60PSI into the pipe, what is my air pressure coming out of the little holes? And how do I find out the CFM the pipe is consuming? Please help!
  5. N

    Do gravitational waves penetrate black holes?

    According to General Relativity, do gravitational waves penetrate black holes? My gut feeling says "no, if gravitational wave goes under event horizon, it won't re-emerge", but I'm not an expert...
  6. T

    2nd event horizon in black holes

    I recently saw a video where it was stated that black holes may have an inner 2nd event horizon where beyond it is trapped light and energy! I have searched the web for an explanation pertinent to this hypothesis but found nothing. Can anyone shed some light (if possible)?
  7. G

    Time reversal in General Relativity, and black holes

    Plain old Newtonian mechanics is time-reversal invariant, i.e. if you view a recording of some events played backwards, it would still appear to be following the same physical laws (gravity attraction law in particular). This type of "time reversal" is exactly equivalent to just turning every...
  8. T

    Intuitively - why aren't black holes hot?

    from a layperson's perspective - if a supermassive black hole is more massive than a million suns then why is it cold? An answer in plain english is truly appreciated for the layperson like me.
  9. B

    A few questions about black holes

    A stellar mass black hole is around 10 solar masses, and some stars can be much massive than this. And doesn't a black hole have more gravity than anything in the universe? Does more mass necessarily mean more gravity? If a star is more massive, how can a black hole siphon off material from it...
  10. R

    Gravitational Waves & Neutron Stars/Black Holes: Observed Velocity Decrease

    2 closely orbiting massive objects are predicted to deserve the fabric of spacetime so much that they will release a ripple of gravitational waves. When geavitational waves are released, they slowly loose velocity energy and spiral into one another. 2 pulsars were discovered orbiting each other...
  11. D

    Black holes and gravity basic questions

    are black holes just dead stars with lots of mass which shrunk to small size and got lots of gravity, or an actual hole in space-time? if they're actually holes, where do they lead stuff that gets in them? if they're just dead stars with lots of gravity, their mass must grow over time because of...
  12. valentin mano

    Black Holes: Event Horizon, Singularity & Information Loss

    the time for crossing the event horizon is infinite,so no singularity,no evaporation and no loss of information could be observed?
  13. M

    Black Holes - the two points of view.

    I wish to take up a discussion between Elroch and DrStupid in RossiUK’s topic “First Post – a question about Black Holes and Gravity”. My post is essentially an exposition of Elroch’s view, which I have shared for many years. Elroch’s exposition was very sedate, and I feel it needs to be shouted...
  14. D

    Why can't Light Escape Black Holes?

    If light is transmitted by photons and photons are massless and gravity only affects particles with mass, then why can't light escape black holes' giant gravitational force?
  15. T

    How Long Do Black Holes Last Before Vaporizing?

    how long do black holes last before they vaporize?
  16. A

    Atwood machine with two holes in pulley.

    Homework Statement A system consists of a pulley and two masses m1, m2 haning from it as shown in the figure. The pulley is a disk of radius R with constant mass density that has two circular hole with radius R/2. Find the angular acceleration of the pulley. Figure attached. Homework...
  17. E

    Kaons, Black Holes, and Particle Physics

    I was on Youtube the other day and found a series of videos that explain the four fundamental forces in terms of a basic particle called the kaon. I basically understood the first 13 videos, but at video 14 I was lost. In the first few videos, they explain gravity, basically stating that it is...
  18. D

    Computer plot of particle orbits around Kerr black holes

    Hi there, First post, so be gentle. I'm currently doing a project on Kerr black holes, part of which is based on a project in Edwin F. Taylor's book "Exploring Black Holes" (the chapter is found here) as well as some of Hartle's book (chapter 15). Part of my project, and as a way of better...
  19. Islam Hassan

    Relativistic Jets from Supermassive Black Holes?

    If nothing can escape black holes, how are relativistic jets of particles and radiation emitted from the supermassive variety of the same? Are they emitted from the BH proper or from something else? IH
  20. D

    Exploring the Truth About Black Holes: Debunking Common Misconceptions

    Are they really black? And are they really holes? I'd say they are actually neither. Would I be right?
  21. D

    Why are black holes shaped like hurricanes?

    If a black hole is a center of unbelievable gravitational force why is it always illustrated as a hurricane? These depictions remind me of a drain in one's bath where the water swirls in from the sides and drops in through the top of the drain. Wouldn't objects be drawn in centrally from all...
  22. J

    Relation between the sol, mass, gravity, and black holes

    I'm a fan. Not a physicist or astronomer.. But this question is bothering me. If the mass of an object increases to infinity as it approaches the speed of light, does that also create infinite gravity at the object? And if so, if we consider the gas swirling around the black hole is very...
  23. C

    Why should rotating black holes emit particles?

    In a brief history of time it says theft 'according to the uncertainty principle rotating black holes should emit particles'. However I do not understand why rotating black holes need to emit particles according to the uncertainty principle. I do understand why black holes emit particles it...
  24. A

    Are black holes the great organizers of the universe?

    [Correct me if I'm wrong about anything ;) ] We once though that the rate of expansion over that universe was slowing down. However, we now see that it's actually speeding up and the present theory is that matter will eventually move so fast that current laws of attraction will devolve and...
  25. U

    PN junction diode barrier potential attracted to free electrons or holes?

    I am wondering about the barrier in PN junction diode.Due to diffusion negative ions are formed on the P side and Positive ions are formed on the N side of the diode.both opposite sides exert force of attraction and so a line of positive ions and negative ions align along the junction. The...
  26. mrspeedybob

    Dim Stars: Are There Almost-Black Holes in the Universe?

    If there were a star which was almost, but not quite massive enough to become a black hole it seems as though gravitational time dilation should make it appear very dim. If time dilation resulted in 1/1000 of the time passing within the star as passes for us, we should see a star emitting 1/1000...
  27. E

    Question about white/black holes

    hey every one! according to what I've read white hole are assumed (in some theories) to be the 'exits' on the other side of a black hole. Where the matter sucked in by a black hole is expelled on the other side creating a new universes in a sort of 'bubble' if you will. Going along with this...
  28. D

    Virtual particles inside black holes

    First time poster, more of a nerd than an academic. So virtual particles, can they pop into and out of existence inside the event horizon of a black hole? What about in the black hole itself? If nothing can escape and matter is torn apart, what happens to those quantum particles? Or maybe...
  29. W

    Messenger particles and black holes

    In General Relativity gravity is described as being a consequence of spacetime geometry. In Quantum Mechanics the different forces are described as being mediated by quanta. One of the predictions of QM is the existence of a particle that mediates gravity, namely the graviton. What I do not...
  30. J

    Black Holes and Quantum Field Theory

    Now, I must preface this by saying that my understanding of QFT is limited, and my understanding of GR is even more so. Nevertheless, I was reading about the No Hair Theorem, and it seemed to me to be suggestive of the indiscernibility of Quantum Particles. Obviously, for a macroscopic black...
  31. Drakkith

    Black Holes: Infalling Observers and BH Evaporation

    Assuming that black holes do in fact evaporate via Hawking Radiation, how can an infalling observer ever get inside the event horizon if the black hole evaporates in a finite time from an outside observers frame?
  32. B

    Can black holes be disintegrated from a sufficiently powerful explosion?

    Can black holes be disintegrated by a sufficiently powerful explosion? If an explosion from various types of astrophysical phenomena occurs near a black hole, can the explosion disintegrate the black hole if the force of the explosion is greater than the gravitational force of the black hole?
  33. V

    Black Holes as 2 Dimensional Objects

    Sorry, new here, and my actual mathematical training is v.limited, so I have to restrict myself mostly to thought experiments, alas. Anyway... Whenever I study up on black holes, it doesn't take very long before the text or discussion quickly devolves into how impossibly abberant...
  34. R

    Black holes and an argument I'm in

    Ok so I am in an argument with my mother about the nature of black holes. She is religious and has classical physics knowledge up to degree level (she has a master's in mechanical engineering) and is very, very stubborn. Ok so she has a theory that physicists have simply arrogantly overlooked...
  35. T

    Black holes and the event horizon

    I'm curious - once an object passes the event horizon the image of that object remains on the event horizon only to become more redshifted rather than dissipating. two questions: 1) why does the image remain if the light stops traveling? if the light cannot travel to the observer, than there...
  36. T

    Are Charged Black Holes Just a Myth?

    Hi, I've been thinking about the concept of charged black holes. What I'm wondering is this; if light cannot escape a black hole, and photons are the bosons of the EM force, then is it meaningful to describe a black hole as having a 'charge'? If the photons can't escape the black hole, then no...
  37. C

    Pauli Exclusion Principle in Black Holes.

    Good evening. I have been reading that the repulsion generated by the Pauli exclusion principle barely prevents neutrons in neutron stars from occupying the same quantum states (after all, they are fermions). However, the principle seems to be violated in a black hole, given that fermions are...
  38. F

    Exploring the Phenomenon of Sound Waves Near Black Holes: A Fascinating Study

    Hi, I'm doing some research on sound. I'm interested in finding out what happens to a sound wave just BEFORE it reaches a black hole and what happens when it ACTUALLY reaches a black hole ? Can someone direct me to the right place for this ? Thanks for the help
  39. T

    Will charged black holes evaporate?

    Black holes only emit hawking radiation which is black body radiation. If black holes only emit photons then the black hole can never get rid of charge which means it can never get rid of all its mass. Does this means black holes also emit charged particles?
  40. T

    Understanding Black Holes: Perspectives and Questions

    I want to clarify some stuff about black holes and have some questions: 1) From the perspective of a hovering near the event horizon observer an external universe evolve at very fast rate. But from the perspective of a free falling observer an external universe slows down. Correct? 2) If...
  41. B

    Exploring the Limits: Planck Units and the Singularity of Black Holes

    Do Planck units apply inside of black holes? Are they modified? Or are they irrelevant? If some Planck units remain unchanged and applicable in black holes, which ones would those be?
  42. C

    Black holes slowing as they pass each other?

    I understand that a gravity well bends space-time such that, close to it, time passes "slower" than further away. The archtypical example is that if a chronometer were dropped into a black hole, we would observe it to tick slower and slower as it approached the event horizon. Based on this, I...
  43. D

    Time Travel - Between two Kerr metric black holes w/detached event horizons

    So imagine your on Earth at a latitude of 30 to 45° N, between two rotating Kerr Metric Blackholes with detached event horizons (dual singularities) allowing you to be shielded from the crushing force of the black holes. Which way do the rotating black holes need to rotate for the past and...
  44. Q

    Mass Moment of inertia of a cylinder with 4 holes?

    Homework Statement Hi I was reviewing for my final and I came across this problem: Problem: Basically there is a 6in long cylinder with dia = 24in Given weight density: 490 lb/ft^3 Each Hole is drilled symmetrically, each has 6in dia and equally space around a 10in dia circle concentric with...
  45. Q

    Mass Moment of inertia of a cylinder with 4 holes

    Hi I was reviewing for my final and I came across this problem: Problem: Basically there is a 6in long cylinder with dia = 24in Given weight density: 490 lb/ft^3 Each Hole is drilled symmetrically, each has 6in dia and equally space around a 10in dia circle concentric with the cylinder...
  46. F

    Modeling bolt holes as stress concentrators in I beam bending

    curious as to the proper way to model this. beam is symmetric so centroid is in the middle (used to calculate distance from centroid d in bending moment of inertia equation) bending moment of inertia is I =\sum(I + Ad2) I=\frac{1}{12}bh b=base h=height d=distance of the area's...
  47. M

    List of Questions about Black Holes

    So from what I understand, virtual particles that are created at the edge of a black hole can become the small detectable radiation (hawking radiation) if one of the particles falls into a black hole, becoming a real particle (its partner now no longer has to annihilate with it) and the second...
  48. C

    My random thoughts about the sun, black holes, and gravity.

    I'm a huge noob and I don't know much about physics and space and stuff, but I was thinking about this in the shower today.. Anyone care to comment? Or correct me on anything? Ok, so I was talking about to Daniel about Gravity, the Sun, and Black Holes.. (Yes we are ghetto nerdy xD) And i...
  49. F

    Question about galaxy formation and black holes.

    In another topic, a member dave13214321323 or whatever his name is :p said that the popular opinion is that in the early universe gas contracted into denser spaces forming galaxies and black holes were consequences of galaxy formation, not the other way around; Black holes at centers of galaxies...
  50. T

    Entering supermassive black holes

    I often see, when people talk about black holes, someone claim that since there are no huge tidal effects at the supermassive black hole's event horizon, that someone on a spaceship falling into such a black hole would not be destroyed and would survive, continuing inwards, until, after some...
Back
Top