What is Compression: Definition and 632 Discussions

Lossless compression is a class of data compression algorithms that allows the original data to be perfectly reconstructed from the compressed data. By contrast, lossy compression permits reconstruction only of an approximation of the original data, though usually with greatly improved compression rates (and therefore reduced media sizes).
By operation of the pigeonhole principle, no lossless compression algorithm can efficiently compress all possible data. For this reason, many different algorithms exist that are designed either with a specific type of input data in mind or with specific assumptions about what kinds of redundancy the uncompressed data are likely to contain.
Lossless data compression is used in many applications. For example, it is used in the ZIP file format and in the GNU tool gzip. It is also often used as a component within lossy data compression technologies (e.g. lossless mid/side joint stereo preprocessing by MP3 encoders and other lossy audio encoders).
Lossless compression is used in cases where it is important that the original and the decompressed data be identical, or where deviations from the original data would be unfavourable. Typical examples are executable programs, text documents, and source code. Some image file formats, like PNG or GIF, use only lossless compression, while others like TIFF and MNG may use either lossless or lossy methods. Lossless audio formats are most often used for archiving or production purposes, while smaller lossy audio files are typically used on portable players and in other cases where storage space is limited or exact replication of the audio is unnecessary.

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  1. S

    Calculate Air Temperature During Compression - TurboFast

    is equation T2=T1*(p2/p2)^((k-1/k)) correct to calculate air temperatute during compression from 1bar to 2bar in a radial compressor? and equation for temperature drop throug intercoller T3=T2-ICefficiency*(T2-ambient_air_temp). Is this equation really so simple, what about air density when...
  2. M

    Spring compression distance

    Given: Load of sacks have total weight of 2250 N and each sack weighs 225 N, how far will each of 2 springs in one system be compressed (spring coeff = 2200 N/m) when a sack is put on it? Energy init +work=final Energy 2250=1/2(4400)x^2 1.02=x^2 x=1.01 Not sure where to go from here.
  3. F

    General Rule for Spring Compression?

    Homework Statement A block of mass m slides on a horizontal frictionless table with an initial speed. It then compresses a spring of force constant k and is brought to rest. How much is the spring compressed x from it's natural length. Homework Equations ??
  4. F

    General Rule for Spring Compression?

    Though this is part of my homework I posted it here because it's a general rule that applies to all physics and doesn't contain specific values from my homework. A block of mass m slides on a horizontal frictionless table with an initial speed. It then compresses a spring of force constant k...
  5. K

    How can I calculate the compression of a support column under a heavier weight?

    Homework Statement A support column is compressed 2.46 x 10^ -4m under a weight of 5.42 X 10^5N. how much is the column compressed under a weight of 4.8 X10^6N? Homework Equations F=KX The Attempt at a Solution By using that equation, I get 542000 = .000246K Solve for K, and I get a...
  6. J

    What is the maximum compression of the spring

    Homework Statement A mass is initially held in place at the top of a spring. When it is let go, it falls and compresses a spring. What is the maximum compression of the spring. Homework Equations f=-kx The Attempt at a Solution I know the solution is to equate mg and kx to find x...
  7. Y

    Differentiation of compression factor

    Homework Statement The problem reduces the derivative (dZ/d(1/V)) to (dZ/dV) x (dV/d(1/V)), where Z is the compression factor and v is molar volume. It further shows that it equals -V^2(dZ/dV). I don't know how they arrived at that value because by my logic it should be 1/(-V^2)...
  8. E

    Thermodynamics - Compression Work

    Hey guys and girls, I wouldn't consider this a homework problem because I'm not in school. I'm just starting to prepare for next aprils GRE exam and so I was reading some thermo stuff from Daniel Schroeder's Introduction to Thermal Physics. I'm working on a problem from his book that...
  9. B

    Solving for Spring Compression: A 0.10 kg Wooden Block

    Homework Statement A 0.10 kg flat wooden block is sitting on a vertical massless spring of spring constant 2000 N/m. An identical block is dropped from a height of 1.00 m above the first block. The collision between the two blocks is perfectly inelastic. How far down is the the spring...
  10. J

    Highest achievable compression frequency

    I am wondering what the upper limit for frequency is currently as far as audio signal generators go. Basically I want to know how high of a frequency I can get on a compression wave. I don't mean the theoretical limit based on the atomic spacing in the medium, but rather if I want to buy a...
  11. F

    Elastic Deformation through compression (stress)

    1. The total cross-sectional area of the load-bearing calcified portion of the two forearms bones (radius and ulna) is approximately 2.16cm^2. During a car crash, the forearm is slammed against the dashboard. Tha arm comes to rest from an initial speed of 81.9km/h in 7.72 s. If the arm has an...
  12. V

    Thermodynamic polytropic compression

    Homework Statement I'm reading through my textbook and doing examples on polytropic process. I see this step and cannot figure out how the textbook gets V3 = 0.0169 m3 P2V2n = P3V3n (500 kPa)(0.05364 m3)1.2 = (2000 kPa)V31.2 V3 = 0.01690 m3 Homework Equations Not sure what to add...
  13. J

    Maximum Compression of buffers for a Train

    Homework Statement I need to work out the maximum compression of buffers for a train with 1.2kg mass, traveling at 0.45m/s and the spring constant, k, is 4.8x10^3 Nm^-1 Homework Equations I tried using 1/2kx^2 but I don't know if I am doing it right The Attempt at a Solution I...
  14. U

    Compression of a sphere underwater

    Homework Statement A solid metal sphere of volume 1.05 m^3 is lowered to a depth in the ocean where the water pressure is equal to 1.38 x 10^7 N/m^2. The bulk modulus of the metal from which the sphere is made is 9.9 X 10^9 N/m^2 Given: The atmosphereic pressure is 1.013 10^5 Pa. What is...
  15. P

    Inelastic collision, spring compression

    A block of mass m1 = 1.8 kg slides along a frictionless table with a speed of 10 m/s. Directly in front of it, and moving in the same direction, is a block of mass m2 = 4.4 kg moving at 2.8 m/s. A massless spring with spring constant k = 1160 N/m is attached to the near side of m2, as shown in...
  16. L

    How do I find the maximum compression of a spring?

    Homework Statement A linear elastic spring can be compressed 0.10m by an applied force of magnitude 5.0N. A 4.5kg crate, moving at 2.0m/s, collides with this spring. What will be the maximum compression of the spring? x= 0.10kg F= 5.0N m= 4.5kg v= 2.0m/s Homework Equations I'm not...
  17. E

    How to Find Maximum Spring Compression from Dropped Mass?

    Homework Statement A block of mass m = 2.0 kg is dropped from height h = 55 cm onto a spring of spring constant k = 1960 N/m (Fig. 8-36). Find the maximum distance the spring is compressed. Homework Equations PEspring=1/2 kx2 F=-kx PE gravity=mgh KE gravity=1/2mv2 The...
  18. E

    Finding spring compression using PE

    How do you do this? A block of mass m = 2.0 kg is dropped from height h = 55 cm onto a spring of spring constant k = 1960 N/m . Find the maximum distance the spring is compressed. m
  19. B

    Maximum compression of spring.

    Homework Statement I know the mass of the block and it's velocity when it contacts the spring and the spring conststant. It is on a horizontal frictionless surface. Homework Equations The Attempt at a Solution I know there is an equation to find the but I just cannot find it in my...
  20. S

    Can Compression cause Thrust?

    What if someone took a jet engine and took out the combustion and turbine mechanism. Then that person found an outside source to power the compression mechanism. Can the compression mechanism alone produce significant thrust? That is, with an outside power that does not add heat into the system...
  21. H

    Spring Compression and block of mass

    Homework Statement A block of mass 12.0kg slides from rest down a frictionless 35degree incline and is stopped by a strong spring with a force constant of 3.00 x 10^4 N/m. The block slides 3.00m from the point of release to the point where it comes to rest against the spring. When the block...
  22. T

    Tension or Compression: Determining the Forces on a Hinged Support Point

    The figure shows a weight W supported by two light rigid rods P and Q. The rods are smoothly hinged to the wall and mounted in the same vertical plane. Which rod is in compression , is in tension?
  23. G

    Truss compression and tension forces help

    The space truss showin has compression and tension forces acting in the members as shown. Force F is 10kN, determine the three unknown forces (F1, F2 and F3). I know that it should be the summation of Fx, Fy and Fz, however for F1, there is no reaction force, so I don't know what to...
  24. C

    Equation for work of a reversible isothermal compression

    I need to find the equation for the work of a reversible isothermal compression of 1 mol of a gas in a piston/cylinder assembly if the molar volume of the gas is given by V= ((RT)/P) + b where b and R are positive constants. Not sure what to do .. please help! THANKS
  25. K

    Estimation of Work in Gas Compression - Thermodynamic

    What kind of thermodynamic process is the compression of a gas when the volume varies reducing it, and the temperature increase, and there is an exchange of temperature with the exterior (the walls of the compressor are refrigerated, but I assume that the gas will increase its temperature a...
  26. G

    Understanding Hook's Law and Compression of Springs

    Homework Statement If a person holds a 30cm spring and compress on it with a force of 100 N (where k = 1000 N/m), by how much is the spring shortened. Homework Equations Hooks ' Law: F = -k* deltaX The Attempt at a Solution The answer for this is 10 cm: 10 = -1000...
  27. Ookke

    Length contraction compression and Schwarzschild radius

    We could imagine a rod moving fast enough to compress it within its own Schwarzschild radius. Should it collapse into a black hole? Or is the rod's own reference frame, where it isn't compressed, the one that makes decisions here?
  28. D

    Needing a second opinion on data compression scheme

    Over the last 2 years, i have been developing a compression technique that is free of "mathematical" expressions. By doing this, the compression scheme would be free of traditional mathematic limitations usually applied to compression routines. I'll go right into it, please let me know if i...
  29. K

    Isentropic compression and humidity

    Trying to assess how relative humidity impacts COT, compressor outlet temperature, on a turbo charger compressor. It appears that humdity reduces gamma in the temp prediction formula, thus reducing COT. Dry air results in increased COT, and humdity reduces it. Any opinions on this?
  30. E

    Compression and temperature

    If say a cylindrical piece of material with a high yield strength is compressed in a vice with a force approaching the yield strength, will the temperature be affected? What about its resonance frequencies? Does shape affect the maximum yield strength?
  31. A

    Calculating Spring Compression from 1m Jump on Scale

    If you stand on a bathroom scale, spring inside compresses .6mm, and tells your weight is 710 N. Now if you jump on the scale from a height of 1m, what does the read at it's peak? This is what I tried to do: I used Hooke's law: F_{}s= k*x and solved for the k which is spring constant...
  32. N

    Compression of a Jaguar XK8 Cylinder

    Homework Statement A Jaguar XK8 convertible has an eight-cylinder engine. At the beginning of its compression stroke, one of the cylinders contains 499 cm^3 of air at atmospheric pressure (1.01 x 10^5 Pa) and a temperature of 27.0 degrees celsius. At the end of the stroke, the air has been...
  33. A

    Compression and Tension Formulas

    hey is there a formula for compression and tension? if so would you be able to let me know what they are? thanks! :)
  34. U

    Volcanic heat from compression or just friction?

    The interior of the Earth is hot enough to melt rock. Obviously friction plays a role. But does compression also heat rock? If yes, what is the underlying chemical mechanism, perhaps an exothermous reaction, that heats rock?
  35. R

    Solve Spring Compression Problem: Work & Energy Approach

    Homework Statement Use work and energy to solve the following. A .1 kg ball is placed against a massless spring that has a stretch constant 50,000 N/m and is compressed 2 m. The spring fires the ball straight up. a) How far did the ball rise assuming no friction? b) The ball's actual rise was...
  36. O

    Spring Compression: 2.5kg Block + 4.5kg Block

    Homework Statement A 2.5 kg block slides along a frictionless tabletop at 6.0 m/s toward a second block (at rest) of mass 4.5 kg. A coil spring, which obeys Hooke's law and has spring constant k = 860 N/m, is attached to the second block in such a way that it will be compressed when struck...
  37. S

    Calculating amount of compression a bone can withstand

    Please I need help with this question. I know I have to use the stress = elastic modulus x strain equation, but i do not know how to apply it to this particular problem. A Bone has a young's modulus of about 18 x 10^9 Pa. Under compression, it can withstand a stress of about 160 x 10^6 Pa...
  38. V

    Compression Ignition Engines: Converting kmol/kmol to kmol/kg Fuel

    Hey guys, Just trying to understand this piece of information I have been given. It is for a compression ignition engine. I can see where they get the 115.954 kmol/kmol fuel and 120.204 kmol/kmol fuel from but don't understand how to change the units 0.7027 kmol/kg fuel and 0.7285 kmol/kg...
  39. E

    Thermal Compression + Expansion Index

    Could anyone tell me what the compression and expansion is used for in a Thermodynamics situation? What is the notation for Compression and Expansion in a formula? I am trying to calculate work done by a heat engine. Thanks
  40. E

    Compression and Expansion Index

    Could anyone tell me what the compression and expansion is used for in a Thermodynamics situation? What is the notation for Compression and Expansion in a formula? I am trying to calculate work done by a heat engine. Thanks
  41. N

    Adiabatic Compression Temperatures

    Hi, When a gas is compressed, its temperature increases. But what is the formula to calculate this rise? Could you please explain the formula too. This isn't homework btw! Thanks!
  42. C

    How Does Compression Work Differ for Van der Waals Gas vs. Ideal Gas?

    One mole of a van der Waals gas is compressed quasi-satically and isothermally from volume V1 to V2. For a van der Waals gas, the pressure is: p= RT/(V-b)-a/V^2 where a and b are material constants, V is the volume and RT is the gas constant x temperature. For the first part of the...
  43. M

    Discovering Gas Compressibility: 8th Grade Science Fair Project

    Hello everyone. We are working on a 8th grade science fair project. We are trrying to conduct experiments that will let us find the relationship of a particular gas's compressabilty and its temerature increase when compressed. We are trying to make the project reletivly advanced, and hope to be...
  44. J

    Cryptography Questions: XOR && Compression

    I have been reading a bit about cryptography recently, and there are a few things that I haven't understood so far: #1) I read that since compression removes redundant information, it is a randomizing function. Does that mean that I would have more high quality random data afterwards if I...
  45. M

    Exploring the Doppler Effect: Compression & Complex Formulas

    I have a few questions concerning the Doppler Effect, I know what it is in terms of a moving object, and how speed effects fequency etc. but I'm more interested in the explantions. My actual knowledge of the two explanations is reasonably vague. The one I am interested in is the compression...
  46. T

    Magnetic Compression: Exploring Potential Uses

    Despite my very limited knowledge on magnetic fields and nuclear fusion being a high school student; I am curious whether you can take a perfect hollow sphere; and (if possible) wrap magnet wire around the shell in such a way that has a magnetic field on the inside of the container...
  47. B

    Compression in composite bars

    Homework Statement A Concrete column 2M in height 100mm in diameter and containing four steel rods each at 15mm diameter calculate the stress and the amount the column is compressed due to the load of 9Kn. the modulus of elasticity for the concrete (in this case) is 20GPa and for the steel its...
  48. J

    Understanding Spring Constant: 8.0kg Stone Compression

    The first part of this problem says that a 8.0kg stone rests on top of a spring, and compresses it by 10.0cm. It then asks what the spring constant is. This is the work I did (assuming g = 10m/s^2, not 9.8m/s^2): (8.0kg)(10m/s^2) = 1/2k(10cm)^2; 80N = 50cm; k = 1.6 But, the textbook says...
  49. I

    Rapid adiabatic compression - puzzle

    I want to know if in rapid adiabatic compression of a gas, is work done by gas on surrounding (atmosphere) numerically same as work done by surrounding on the gas. Please tell if there exists some solid proof of the answers you guys are giving.
  50. T

    Change in entropy, Gibbs and Helmholtz in an isothermal compression

    Homework Statement Determine the change in the entropy, Helmholtz free energy, and Gibbs free energy, when a mole of ideal gas is compressed from 1atm to 100atm at 20C. The Attempt at a Solution I am not entirely convinced by my attempt below -- can anyone spot something wrong? (I thought it...
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