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. Burt

    A What Is a 'Black Hole' & What Does It Mean for Particles?

    When they talk about information falling into a black hole, are they referring to the basic defining parameters of the particles falling into the hole?
  2. STAR GIRL

    I What happens to the information entering a Black hole?

    What happens to the information entering to the Black hole??
  3. YZEDY1one

    I Thought experiment- Dropping a rope into a Black hole

    Hi, Physics Forum! I've been wondering what would happen in the following thought experiment. I am not physicist and may have made some incorrect assumptions. Please explain if any of these assumptions are wrong. What would happen if you threw a piece of (very long and strong) rope into a...
  4. B

    I Can an Atom Become a Black Hole?

    If you shrunk an atom down to a certain point would it become a black hole like all matter in the universe can? How big would it be?
  5. DIGBY STILLS

    B Is it possible Earth is a black hole?

    Yes I know. Sounds silly. I'm not a physicist, but it occurred to me to wonder: is it possible Earth is a black hole with data encoded in two dimensions on its surface? What would the proofs look like? Discuss.
  6. G

    I How Much Thrust is Needed to Hover Above a Black Hole?

    Let's say that I'm hovering using a jetpack at a fixed distance above the event horizon of a black hole. And that I'm perfectly well shielded from any radiation and whatnot. Its a supermassive black hole with a super large Schwarzschild radius, so tidal forces are minimal. Approximately how...
  7. R

    I Are quark stars a realistic solution to the black hole singularity problem?

    Is this a realistic solution to the black hole singularity problem, Going beyond that, neutrino stars?
  8. T

    Gravitation force of a disk with a hole

    Homework Statement [/B]Hello, I have derived the equation for the gravitational force for a disk to be 2Ggm/a^2(1-x/sqrt(a^2 - x^2) when an object is added on top of the system. My question is would the force still be somewhat similar if the disk now had a small hollow of radius c...
  9. BillTre

    What Creates the Giant Whirlpool at Dam Overflows?

    Giant standpipe type overflow from a dam. https://rumble.com/embed/vfzc9/
  10. SD das

    I Does a black hole cut the fabric of spacetime as it changes

    Einstein's general theory of relativity describes the stars distort spacetime fabric and it appears a black hole makes a hole in the spacetime fabric. It is evident that the size of a galaxy does not change due to gravity but in large scale the distance between two distant galaxies increases due...
  11. S

    Force needed for hole punch in Metal

    Homework Statement A punch is used for cutting an (approximately) circular hole with a diameter of 35 mm through a metal sheet 0.2 cm thick. If the shear strength of the metal is 80 MPa, estimate the force needed to punch the hole. Make it clear how you have calculated this value. Homework...
  12. C

    Oscillation in a hole through the Earth (hole is offset)

    1. The problem statement, all variables and given/known There is an Earth but the hole is not in the middle but the side.find the period of oscillation Homework Equations Simple harmonic equation.Newton gravitational force The Attempt at a Solution I got GMx/R^3+acc=0 so period of...
  13. Nabin kalauni

    Pulling a puck through the hole

    Homework Statement Its a classic problem about a puck that is rotating on a frictionless tabble with a velocity v1 and radius r1. It is is connected to a string which runs through a hole a the centre of the table. The string is pulled from below until the radius decreases to r2. Find the work...
  14. sophiecentaur

    Stargazing Understanding Kidney Beaning in Wide Field Eyepieces

    I bought myself a nice 32mm (2" fitting) eyepiece with a 'wide view'. I was disappointed to see a dark patching the middle when I looked through the scope in daylight. I have never been aware of this when looking at (brilliant) wide objects at night. With its wide angle view, it gives the...
  15. top12eaper

    Moment of inertia of cylinder with a rectangel shaped hole

    i know how to calculate the inersia for the cylinder, than i have to take away the inersia of the rectangel, but i can't find an equation for the inersia for a rectangel with the plane spinning perpendicular to the rotation axis, please help !
  16. K

    Understanding Compressive Stresses in a Plate with a Hole Under Uniaxial Loading

    Is t right that, in a plate with a hole, subjected to uniaxial loading, along one of the axis, one gets compressive stresses around the crack tip (in the same direction as that of the applied load ). I'm not able to understand this intuitively. Can someone help? I believe, intuitively, these...
  17. S

    A Defining the surface gravity of a black hole

    Consider the following two definitions of the surface gravity of a black hole (taken from page 23 of Thomas Hartman's lecture notes(http://www.hartmanhep.net/topics2015/) on Quantum Gravity): 1. The surface gravity is the acceleration due to gravity near the horizon (which goes to infinity)...
  18. Go Nucelar

    B Adding a huge electric charge to a black hole?

    I wonder, what would happen if you started dropping lots of electrons into an existing black hole which otherwise doesn't accrete any new matter? The charge of the black hole would build up much faster than the mass. Wouldn't its charge become so high at one point that further electrons would...
  19. Jewelz

    Moment of Inertia of a Spinning Record with a Hole in Center

    Homework Statement A 45 RPM record is a disk with a wide hole in the center. The mass of such record is 45g. It is 7 inches in diameter, and the hole in the center has a 1.5 inch diameter. (Sorry for the odd units, this was the way it was given). Find the moment of inertia of the 45 RPM...
  20. snoopies622

    B What do I see while falling into a black hole?

    If I fall into a Schwarzschild black hole and, as I'm falling, look in the direction away from it, what do I see? I once heard someone say the rest of the universe would appear to move faster and faster, and as I cross the event horizon it would appear to move infinitely fast. I'm not sure...
  21. D

    Drag formula used to calculate bullet hole depth?

    I'm writing a real time 3D physics simulator that simulate bullet ballistics. Can I use the air drag formula that factors in drag coeficient and outputs drag force to calculate how deep a bullet will penetrate a target material? Say I substitute air pressure with target material density. And...
  22. S

    A Black hole as topological insulator

    Hi, is anyone familiar with topological insulator? I read an interesting paper: http://arxiv.org/abs/1703.09365, Black hole as topological insulator Abstract: Black holes are extraordinary massive objects which can be described classically by general relativity, and topological insulators are...
  23. T

    B Finding Black Holes: Possible or Not?

    If space were like a ocean of ice chunks where everything gradually moves apart and the andromeda galaxy and our galaxy are moving closer to one another. Finding the connection point would find a black hole right. Or is that not possible with the way space moves?
  24. A

    I Gravitational time dilation calculation near a Black Hole

    Hello to everyone! I am trying to understand in practice the Gravitational Time Dilation by calculating the time distortion near the supermassive black hole Sgr A* in our Galactic Center. According to Einstein's Theory of General Relativity, the time distortion near a black hole is calculated...
  25. C

    I Dragging a wormhole into a black hole

    Assuming a wormhole exists, what would happen if one took one end of the wormhole into a black hole. Could they enter the wormhole and leave the black hole? What would be the result if they did?
  26. K

    I Size and shape of a black hole singularity?

    How and if singularity is related to Plank size (h) , are they be related ? If they are; can the singularity have squared shape (like pixel) , if it is h size so that is the "smallest" understand by "physics" and any curve (circle) would break the rule of h begin the smallest ? Does my question...
  27. SlowThinker

    B  Charged Black Hole Hawking Radiation: Answers to Questions

    I was thinking about the title but after searching Arxiv, PF and the internet in general, my confusion has only increased. I have a few questions: 1. Often I see units where ##G=c=\hbar=1##, but what is the charge of an electron in these units? Everyone says M=Q as if it was somehow obvious how...
  28. Seth Newman

    How Small Must Mars Be Compressed to Become a Black Hole?

    Homework Statement To what radius do you need to compress Mars in order to turn it into a black hole? Homework Equations None given, but I am mildly familiar with Schwarzschild and his equation. I know that if we double the object's mass, multiply by the universal gravitational constant, and...
  29. Vitani11

    Hole though the Earth and SHM: why is uniform density assumed?

    Homework Statement A particle of mass m is dropped into a hole drilled straight through the center of the Earth. neglecting rotational effects and friction, show that the particle’s motion is a simple harmonic if it is assumed that the Earth has a uniform mass density. Obtain an expression for...
  30. C

    I What is the name for the "stuff" at heart of black hole?

    What is the name for the "stuff" (neither matter nor neutrons) at the heart of a black hole?
  31. Daniel Petka

    B What Happens When a Black Hole Interacts with Antimatter?

    A black hole is basically extremely dense matter. What could happen if it interacted with antimatter? I guess a part of the black hole's mass would annihilate.
  32. D

    Can a photon's energy be so high that it creates a black hole?

    Is it possible for a photon to be so energetic that it forms a black hole? If so, how fast would that black hole be moving?
  33. G

    I What would happen if you moved a black hole?

    Ignoring for the moment the plausibility of this scenario, what would happen? A black hole is the ultimate gravity well, right? In some circles, they're even considered tears in the fabric of the universe. So what would happen to that fabric if you moved the black hole? Would it behave like...
  34. Zan24C

    I The Shapiro delay and falling into a black hole

    I realize that this question has been asked many times on this forum, however, I have yet to come across a satisfying/understandable answer that takes into account gravitational time dilation. Premise: The speed of light inside a gravitational field is slowed down relative to a distant observer...
  35. D

    Rewriting Central Force Problem of Black Hole Potential

    Homework Statement From the homework: In General Relativity it is found that the radial equation of an object orbiting a non-rotating black hole has the form $$\dot r^2 + (1 - 2 \frac {V_o} {r} ) (\frac {l^2} {r^2} + 1) = E^2$$ where ##r## is the radial coordinate, ##l## is the angular...
  36. Arman777

    I Exploring the Black Hole Horizon of Our Universe

    Ok..I know that at some point, from the Hubble Law , galaxies will seem to moving away from us speed of light,But actaully they can't because the space-time itself expands so it will be like a black hole horizon,which within that radius its , c/H , we can observe things etc.But out of that...
  37. M

    B Challenging the Existence of Black Holes: A Critical Analysis of Recent Research

    Hey guys, Does black holes exist? Is it even real?
  38. H

    Studying Rotating black hole & Hawking radiation research

    I am an undergraduate student of a university, I have taken the research topic as Study of Rotating black holes and Hawking radiation which I am really interested. Research description as follows. The geometric invariant are computed in various black hole geometries in several different...
  39. T

    B White Hole as an explanation for the big bang and inflation

    Was the concept of a White Hole ever intended to as a POSSIBLE explanation for the Big Bang, inflation and dark energy expansion of the Universe? Or is it considered crack pottery by the cosmology community? I presume the observable Universe would need to be as small as say a single atom in...
  40. LarryS

    I Exploring the Interior of a Black Hole: Space-Like Separation Beyond the Horizon

    Forgetting about the singularity for the moment, is the interior of a black hole a space-like region? That is, are any two events that occcur past the black hole horizon space-like separated? Thanks in advance.
  41. Jesus

    How to Calculate the On-Shell Action for an AdS Schwarzschild Black Hole?

    Homework Statement I want to calculate the on shell action for the case of a AdS Schwarzschild black hole. Homework Equations Following the case of the flat Schwarzschild black hole I tried to add a counter-term of the type of a Gibbons-Hawking boundary term for flat Minkowski spacetime...
  42. Hepth

    Dynamics of pumping fluid into a cylinder with an air hole?

    I should be able to do this, but its been a while and maybe I'm making this more difficult that it should be. Assume you have a cylinder nearly sealed but with an outlet hole at the top. I want to pump a fluid into the canister, pushing the air out of the hole, and time how long it takes. The...
  43. Leyzorek

    B Can a photon be made energetic enough to escape a black hole

    why can't a photon escape a black hole? i think it is because the photon is red shifted away to nothing, if this is true, it would be possible to create a photon that would be energetic enough that a black hole would not have enough time to red shift it away to nothing, unless there is some...
  44. C

    How Do You Calculate Hole Size from Leak Rate in a Vacuum Vessel?

    Hey everyone!Here's my first post in the forum!You probably usually discuss more substantial issues, but I'm having troubles and I'm sure you can help me!I'm trying to calculate the size of an ideal circular hole in a vacuum vessel given the measured leak rate in mbar l/s (helium spray leak test...
  45. Chris G

    A Q: Black hole event horizon vs distortion effects

    Hello! I'm having a hard time finding realistic black hole simulations, but I saw one recently (black hole size comparison on youtube) that showed the following 3 black holes (attached). I noticed that the larger the black hole, the smaller the "distortion zone" was relative to the radius of...
  46. Elnur Hajiyev

    A Light from the singularity of a charged black hole

    According to Cosmic Sensorship Conjecture, naked singularities are prohibited in General Relativity. To my knowledge, naked singularity means light from the singularity can escape to infinity. In Reissner-Nordström metric, references say naked singularity appears only if ##GM^2<P^2+Q^2##...
  47. Will K

    B Is the Universe Inside a Black Hole?

    "Before the big bang, scientists believe, the entire vastness of the observable universe, including all of its matter and radiation, was compressed into a hot, dense mass just a few millimeters across." Isn't this describing what the singularity of a black hole is? Black holes spin extremely...
  48. G

    What is the diameter of each hole in the shower head?

    Homework Statement In a low-flow showerhead that contains 18 nozzle holes, the volume flow rate of the water is 4.00 L/min and the water maximum speed is 2.70 m/s. What is the diameter of each hole? Do not ignore viscosity of water. Homework Equations Q=Av_max Q=((pi)r^2)v_max...
  49. Brunolem33

    B What is the true nature of the mass of a black hole?

    The question is probably naive, but please don't block this thread before I get an answer... As far as I know, mass doesn't exist by itself, it is rather an "attribute" of matter or, let's say it is attached to particles...no particle = no matter = no mass. Now, inside a black hole...
  50. Singlau

    B Black hole mass and sigma (velocity dispersion)

    It seemed to have been asked before, but I am still a bit confused. How is the velocity dispersion formed? Doesn't the evidence of dark matter tells us that the orbital speed is uniform in a galaxy? Is there a direction of dispersion? (e. g velocity gets larger to the core) And why does...
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