What is Crack: Definition and 56 Discussions

Crack cocaine, also known simply as crack or rock, is a free base form of cocaine that can be smoked. Crack offers a short, intense high to smokers. The Manual of Adolescent Substance Abuse Treatment calls it the most addictive form of cocaine. Crack first saw widespread use as a recreational drug in primarily impoverished neighborhoods in New York City, Philadelphia, Baltimore, Washington, D.C., Los Angeles, San Francisco, and Miami in late 1984 and 1985; its rapid increase in use and availability is sometimes termed as the "crack epidemic".

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  1. person123

    Energetic Size Effect for Tensile Loading

    For quasi-brittle materials, there is an energetic size effect as well as a statistical size effect, as described here. However, it seems to require a stress gradient for it to play a role, as in the example given with a 3-point bending test. The stress at the middle of the fracture process...
  2. Y

    Effects of notch's position along a rod that is in tension

    Say I have a rod with a notch at the very centre and another ro with a notch at the very end. Both rods are identical in length radius materials etc. Who would be impacted by the notch more? And if then both were to support a load at the end of the rod (both in tension), what effects would the...
  3. person123

    I Size Effect on Structural Strength

    I'm using the wikipedia page on Size Effect to get an understanding of it. It identifies Statistical and Energetic size effects and two types within energetic. I believe I understand statistical, as it seems to essentially say that assuming there's some variation in the material strength, the...
  4. M

    Crack Mode I: Stress-Strain Relation

    If i have a thermal shock in a thermo-elastic material with crack mode I propagated ? what are the stress-strain relations in this case? or what is the factor K relation? "sorry if the question is not true, but i hope you understood what i mean"
  5. R

    Under what conditions can glass crack spontaneously?

    Are there any conditions under which glass cracks spontaneously? Just now, my mother's rear windshield cracked spontaneously. The story according to her: Slowly approaching a stop sign. No busy traffic. No trees/animals in sight. Few people. Suddenly, the rear windshield cracked with a loud boom...
  6. E

    Difference between brittle fracture and fatigue crack growth

    My question here is regarding fracture of materials. I have problems in understanding some concepts. Now, for static loading, there is a property called KIC (fracture toughness). By equating our stress from the static load to this KIC, we get the maximum length of the crack which does not...
  7. K

    Central "through" crack with a concentrated load

    Hi, Please consider the problem below of a central through crack with a concentrated load as shown below. Can someone please help where does one come across such a problem in a practical world? How will I have a concentrated load opening the crack? In the physical world, what is that...
  8. Jonathan Scott

    Can you crack GCHQ's code-breaker challenge?

    Nice little puzzle: http://www.bbc.co.uk/programmes/articles/5m5cv4NM5dWx108YgCQXj9J/can-you-crack-gchqs-code-breaker-challenge I didn't find it particularly difficult (less than a minute to spot how to do it, and a few minutes to actually work through it), although Google translate thinks the...
  9. G

    How fast can hackers crack 128 bit file encryption?

    I got a freeware encryption software with only 128 bit. How fast it is for hackers to crack 128 bit file encryption?
  10. DaveC426913

    My TV Cracks: Is It Heat or Discharge?

    I have had a number of TVs - both CRT and flat-screen - that make a loud crack occasionally. It does sound just like appliance settling from heat expansion/contraction, but I'm not so sure that's what it is. It cracks exactly once and only once, and does not seem to be correlated with heating...
  11. I

    What Makes Physics Such an Intriguing Field for Young Minds Like Irvin's?

    I'm 17 years old, I´m mexican and I like physics
  12. R

    Micro laser welding, the picture is a crack?

    Hi guys, My name is Rogelio H. Aguirre, a grad student from the University of Waterloo working on MEMS sensors. Currently, I am working with micro laser welding suppliers to fabricate the packaging of a pressure and a temperature sensor. I have some experience on weldings, but not in micro...
  13. D

    Ultrasonic crack detection in glass bottles

    I'm working on a project for a bottling plant that is trying to make a vision-based machine to detect cracked glass bottles before they attempt to fill them. It seems that the vision & backlight approach is the standard way to do this in the industry, but the shape of the bottle in this...
  14. D

    Can You Decode This List of Numbers into a Message?

    The encryption method is extremely simple and the first letter is already in plaintext (the character number that is). The plaintext is plain english. [79, 32, 79, 39, 45, 39, 112, 21, 50, 64, 37, 5, 107, 4, 36, 87, 35, 81, 48, 94, 57, 92, 46, 93, 125, 9, 102, 70, 42, 69, 51, 86, 92, 5, 106...
  15. R

    Stress at crack tip of a 2D cantilever beam under sinusoidal excitation

    I need some information urgently. I am working on crack of a 2-D cantilever beam. One side of the beam is fixed. I am applying a sinusoidal time varying load on other end in Y-direction.Beam length and width are 100cm and 10cm respectively. crack is 05 cm in y-direction. I have attached data and...
  16. J

    What would crack easier? An iPhone 6 or an iPad air?

    If I took a hammer to each of the screens, which would crack first with a minimum amount of force? If I put a screen protector on it, would it change the answer of which one would crack first? I tried to pick two models which had similar frames. If the using different models actually makes it a...
  17. R

    Which is harder to crack: a smaller or larger screen?

    Is it harder to crack a smaller screen or a larger screen? Why? For example, if I hit an iPhone with a hammer, would it break more or less than if I did the same to an iPad? Would it change which is more safe if I put a screen protector on? The force would be the same in both cases but it...
  18. A

    Glass crack on Aluminum and Copper tungsten

    Homework Statement Here is the issue I met.Could you refer to attached file? 1.We glued one piece aluminum block and one piece copper tungsten block on substrate. The aluminum and copper tungsten block have different height.The glue thickness underneath them is different...
  19. B0b-A

    How long to crack this encryption by brute-force ?

    How long to crack this encryption method by brute-force ? I have a 64 character password created using a simple substitution cypher of the base 64 character set, i.e. all characters are included in the password , none are repeated. How long would it take a modern computer to crack this...
  20. A

    Anyone want to take a crack at my decyphering my prof's handwriting?

    Anyone want to take a crack at deciphering my prof's handwriting? http://i.imgur.com/8rDPmxK.jpg There is a question mark and closing bracket at the end that was cut off FYI. Sorry for the large image. Not sure how to make it smaller.
  21. A

    Why Did the Crack on My Droid Propagate in a Symmetrical, Strange Shape?

    A few weeks ago I accidentally dropped my droid on some concrete :) Impact location was near the top center, slightly offset. I notice that an initial crack propagated downward about 1 in before making a perpendicular split. Each side of the crack continued along the phone glass heading towards...
  22. N

    Modeling a crack in a material.

    I was wondering if anyone has ever tried to model/fit a crack on a material surface with a Weierstrass function.
  23. R

    MATLAB Matlab code for detection of location of a crack using natural frequen

  24. C

    Brittle crack growth in normally ductile materials

    Hey guys, I'm new here so please be easy on me if I break any "unwritten" rules. I'm doing a design study on brittle crack growth in ductile materials. As I understand it, when a macroscopic crack is found in a load bearing plate, holes can be drilled at each end to reduce the internal...
  25. P

    First Crack at Multithreaded Programming

    Homework Statement Create a multithreaded program (Java) that finds a word in a text file and reports the lines one which the word appeared. Word lines should be reported in the order in which they appear. Homework Equations The Attempt at a Solution I know that I can just...
  26. J

    Work (energy) that causes a crack without distance

    If you had a bowling ball sitting statically on top of a perfect rectangluar porcelain tooth, and the bowling ball caused a crack in the porcelain tooth (hairline fracture), but then you immediately took the bowling ball off the tooth... wouldn't there be no work done since the bowling ball...
  27. D

    Can You Crack This Code for a Job as a European Spy?

    http://www.canyoucrackit.co.uk/index.asp If you can crack it, you will get a job as a European Spy! That's the link to where you can attempt to crack the code. You get unlimited attempts! P.S. If anyone gets the code, please feel free to post here, lol
  28. D

    Help needed with crack growth simulation implementing CZM

    Help needed with crack growth simulation in Ansys implementing CZM Hello, everyone! Could you, please, help me with the following issue? I’m trying to simulate a crack growth in an anisotropic media using cohesive zone model (CZM), and the results I get do not agree with my expectations...
  29. M

    QED Proton Size: 4% Smaller Than Thought?

    http://www.nature.com/news/2010/100707/full/news.2010.337.html Apparently the proton is about 4% smaller than thought, which is somewhat challenging for QED. It could be new effects or experimental error of some sort. Any such guessing is speculative at this time, but what would you think?
  30. B

    Is It Possible to Crack a Whip Faster than the Speed of Sound?

    Could you crack a whip while moving faster than the speed of sound?
  31. S

    Understanding Vacuum Physics and the Crack in My Window

    Vacuum Physics? I would like some clarity on a problem I think is attributed to a vacuum space. This is what happened...I have a small room that is 7' x 10', there are two metal doors directly across from each other on opposites sides of the room. It seems that when I want to close the door...
  32. Q

    Why are personal and crack theories not allowed?

    Why are personal and "crack" theories not allowed? I always wondered about this rule. This is a skeptics section of the forum and if you have something to say, well wouldn't it be reasonable to question it and take it apart than to rather disown it? I asked a question earlier about Forces by...
  33. M

    Using a pedulum to crack eggshells?

    my friend and i are doing our science fair experiment on the strength of eggshells. we plan on using a pendulum to crack the eggs but do not know how to calculate the force of the pendulum, which we can then use to find the strength of the eggshell.
  34. S

    Crack Nucleation in Solid Mechanics: Fatigue & Creep Loading

    In Solid Mechanics, what is 'crack nucleation'?? and how does this relate to fatigue and creep loading? thanks
  35. R

    Forces to crack a pouch after a fall

    Hi I have a question I need help with. Im trying to find out how much forces that a pouch (balloon) creates on the inside walls when it hits the floor after a fall. A pouch (balloon) with one litre of water falls from 1 meter down to the floor. How much force must the "walls" stand...
  36. M

    Crack this code if you can* Challenging

    9 30 20 39 59 50 79 73 88 95 104 131 132 135 144 150 166 185 198 190 218 215 232 235 241 269 265 270 300 305 313 325 338 348 355 373 I will not be posting the algorithm used to generate this coded message. Good Luck!
  37. U

    Fracture Mechanics - Crack Propagation and Stress Intensity Factors

    I am trying to determine the critical crack length of a part using finite element analysis. The software I am using (ABAQUS) has the ability to perform fracture analysis. I model the part, create a crack, and ABAQUS will output the stress intensity factors (modes I, II, and III) and contour...
  38. P

    Will Adding Too Much Load Cause a Beam to Crack?

    like if I was to say "this beam can take this much load" does that mean if you put any more load on it, it will crack? Sorry if this is a confusing question, help my understanding if you can.
  39. Z

    Help me with the leakage rate of a crack in a pressure pipe.

    I am thinking about the following situation. In a stagnation water loop, the pressure is building up. A crack occurs due to the expansion of the water. What will be the solution approach to determine the flow rate of the leakage? Please give some hints or references. Thank you.
  40. R

    Will A Temperature Change Caused by Fire Line Crack Mirror?

    Hello, We have an installation in which we will be placing a 1/4" thick mirror which spans 7ft across and 5ft in height directly next to a "line of fire" (a gas pipe with holes which will have a flame approximately 6" in height). Our concern is that when the line of fire is turned on in...
  41. P

    Is Non-Linear Algebra the Key to Solving Homelessness?

    lol if you have time for a 6minute video watch this homeless guy is talking about suposed non-linear algebra. I couldn't follow ... http://youtube.com/watch?v=Tc-kjz9s2IA&mode=related&search= If anyone can follow this to me the numbers just don't seem to add up please explain...
  42. D

    Is This a Running Key Cipher Challenge?

    |1|4|6|9| |D|-|-|-| |S|K|J|A| |Y|U|J|-| |S|G|B|-| |Q|F|J|A| |L|H|U|-| i would love to see anyone break this one i found it on a nothere site that said you could give it away but it took me 5 computer programs that crack encrypted text like that and a few books took me for ever.
  43. dontdisturbmycircles


    I feel justified in making a reusable thread because it is unique to this section. Here's my idea. I take a few sentences or words that make sense and apply simple coding techniques and if anyone cracks it, I move onto the next one. I will not be posting any hints and will not move onto the next...
  44. A

    Is This Complex Infinity Math Challenge Solvable?

    Math Teaser! Can you solve this? [tex] \frac{4 \infty}{\sqrt{-1}} {(1+\sqrt{-1})^(1/\infty)-(1-\sqrt{-1})^(1/\infty)} [\tex] Edit: why this latex is not being generated? Anyway the "expression" is [(4*inf)/sqrt(-1)] * { [1+sqrt(-1)]^(1/inf) - [1-sqrt(-1)]^(1/inf) } where inf stands...
  45. 0

    Crack the Code: Find the Optimal Strategy

    There's a funny flash game where one of the puzzles is to guess a four-digit password with digits from 1 to 8. After each guess, the puzzle gives you some number of x's and some number of o's, with the x's indicating how many numbers you guessed correctly and in the right place, and the o's...
  46. D

    Is my Kasamba.com expert on crack?

    Is my Kasamba.com "expert" on crack? This question is not for school, it's something I'm doing on my own. About a year ago I was told on this board that in theory Mass has no effect on the top speed of an aircraft. Drag opposes thrust, Mass (weight) opposes Lift. Mass may slow down the...
  47. M

    Can You Crack This Number Puzzle?

    a number puzzle... tell me a the lowest number for which the number just below it is divisible by 2 ,the one below that 3, below that 4 ,and below that 5 ,and below that 6 .
  48. Ivan Seeking

    How to crack weird space cases: by Jim Oberg

  49. russ_watters

    Leaving for Mexico at the Crack of Dawn!

    So I'm going back to Mexico tomorrow (today). I thought I was going back at 6:00 tomorrow afternoon, but found out late yesterday that I'd be leaving at 6:00 in the morning. Fabulous. So I decided that rather than get 3 hours or so of sleep I'd take a nap in the afternoon, drink a little, and...
  50. A

    Is Crack Pottery? - Get an Opinion

    http://www.ldolphin.org/energetic.html looks like it to me but i would like other people's opinion.