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. K

    Why does compression of a nerve cause any kind of feeling at all?

    Is it because the charges in the nerve are being pushed away from the compressed area, thus sending electrical signal along the nerve? Why was my post moved from physics forum to biology forum? This question could be classified as both physics and biology as I am asking about charges. What's...
  2. C

    Calculating the change in entropy of an ideal gas under compression

    Homework Statement Initial pressure: 140kPa Temperature: 25C or 298K Volume: 0.14m^3 Final Pressure:1.4MPa or 1400kPa It uses index compression, n=1.25. So PV^1.25 = constant. c_p = 1.041kJ/kg.K and c_v = 0.743 kJ/kg.K Homework Equations ¥ = c_p/c_v ΔS=c_v*ln(Tf/Ti) + R*ln(Vf/Vi) [i...
  3. PetePetePete

    Stress and Strain Coursework Question

    I am struggling with a question in my coursework, and would appreciate some guidance. The question is: The component shown in Fig 1 is made from a material with the following properties and is subjected to a compressive force of 5kN. Material Properties : Young’s Modulus of Elasticity – 200...
  4. ajayguhan

    Isentropic Compression of Saturated Water: Workdone Calculation

    Workdone= integral Pdv a kg of saturated water was compressed isentropically from 1 bar to 10 bar. I solved it in the following logic: Since water is incompressible dv=0 , work =0 But my answers was wrong. The solution was integral Vdp where V is Vf at 1 bar My doubt is , is workdone...
  5. deuel18

    Can a hydraulic compression create endothermic phenomena?

    The title might be a bit confusing but I just want to know if you can recreate (partial) the system of refrigeration with hydraulic compression. So say, you have a container (cylindrical piston) filled with water, then you apply pressure. Will the water's temp increase? Then, will the...
  6. N

    Mechanical efficiency of a compressor #polytropic compression

    Hy please help me .i am strugling to calculate the mechanical efficiency of a compressor as i am not given power output and power output
  7. S

    Frustrated with Adiabatic compression problem

    Homework Statement In a diesel engine air is adiabatically compressed to autoignition temperature (287oC) of diesel. Given C/nR=2.78 for air, and the room temperature is 27oC, what is the compression ratio where diesel vapor is added for ignition.Homework Equations PV=nRT PV=NkT C=(dU/dT) The...
  8. A

    Spring Compression at kinetic energy = 0

    Homework Statement An inclined plane of angle θ = 20.0° has a spring of force constant k = 460 N/m fastened securely at the bottom so that the spring is parallel to the surface as shown in the figure below. A block of mass m = 2.51 kg is placed on the plane at a distance d = 0.324 m from the...
  9. A

    Calculating Torsional Force - Compression Springs

    Let's say I've got a helical compression spring of a known length and strength, and I want to know how much force it would take to twist the spring around the axis of its coils, effectively making the diameter of each coil smaller, so it acts a bit like a torsion spring. I know Hooke's law is...
  10. H

    Air Compression Shoes: A New Idea

    I had an idea for a type of shoe similar yet different from air Nike, and I would appreciate some comments. A hind foot air chamber would be compressed upon a runners foot strike ( with a force up to three times body weight). The air would be pushed through a one way valve into a rigid mid...
  11. H

    Force applied to both sides of a spring. What is the net compression?

    Homework Statement A spring is compressed from both ends by 100 Newtons and the spring constant is given as 1000N/m. What is the net compression distance/displacement (x)? Homework Equations F=-k*change(x) The Attempt at a Solution Initially, I thought that the net displacement would...
  12. H

    For a sound wave how/why does the compression and rarefaction occur?

    I cannot seem to visualize how this compression and rarefaction occurs for example when I clap my hands, I know I move air molecules away from me, but it's so weird that such compression(high air pressure) and rarefaction(low air pressure) occurs. I also do not quite understand why this...
  13. M

    Non-uniform adiabatic gas compression

    I would like some insight on a problem I have been working on. I have a seal container of air where the outside chamber has a slight temperature differential between top and bottom. I understand this causes a density variation in the air between the top and bottom of the chamber. Now I am...
  14. normana

    Ocean water compression question

    To simplify this question, let's say the ocean is 3800 meters deep and 1 meter wide in either direction. Now let's add water equaling 1 cu meter on top. How much higher does the ocean get?
  15. S

    Equation for calculating o-ring compression

    For whatever reason this equation is slipping by me, I don't want to use a calculator though because I am building a spreadsheet. Can someone please tell me the equation to calculate o-ring compression? Thanks
  16. M

    In compression of gas, which is first kinetic energy or heat?

    Hello, when gas compressed it get heated, proper reasons i don't know. If we consider first kinetic energy increases due to external work done but hows that happens? and if we consider heat is first, where from it came? my guess is that when molecules come closer in confined wall( due to...
  17. G

    Designing a Helical Compression Spring with Limited Information

    How do I design a spring given only pressure and the the maximum length by which it can be compressed. I tried using the formula P=F/A but I don't have the force to be applied on that spring.
  18. M

    Variations of compression ratios

    Hi,all. What changes the variations of compression rations in diesel and otto cycles which are always used in the engines. Are there any cycles used in automobile engines other than otto, diesel or seillinger?
  19. P

    How much energy is consumed in reality in steam compression?

    I want to know how much energy REAL steam compressors consume in compressing steam @ 1 kg/sec from 2.56 kPa to 1 bar. Theoretically (with `100% efficiency) it's 141 kW for making 1 kg/sec steam flow assuming that the temperature doesn't decrease due to loss of heat as latent heat of...
  20. T

    Collision of Objects Dropped from Different Heights with Spring Compression

    Homework Statement (a) A block of mass m = 2.00 kg sits on a massless platform supported by a vertical spring with spring constant k = 55.0 N/m. How much is the spring compressed? (b) The block is now lifted off the platform and dropped from a height h = 1.5 m above the platform and...
  21. M

    Finding spring constant K and compression distance

    Homework Statement https://scontent-a-sjc.xx.fbcdn.net/hphotos-frc3/t1.0-9/10294335_1407511836191702_8633020308624670643_n.jpg Homework Equations PE=.5kx^2 F=-kx The Attempt at a Solution I honestly just don't know how to approach a problem where you have to find both the...
  22. J

    Helical conical compression spring design

    I am designing a constant pitch, helical conical compression spring (round wire cross section) that will be compressed into a final desired shape. So my issue at hand is figuring out the pre-compressed geometry that will give me my desired final geometry once compressed. The compression will...
  23. michael879

    Black Hole via charge compression

    Here is my basic question: Lets say we have a massless charged shell with charge q and radius R. Is there some R where a black hole is formed? I haven't work this out with the EFE, but the calculations I've done are relativistic (GEM equations instead of EFE, for simplicity). I found that...
  24. zoobyshoe

    What are acceptable compression test readings for a 4 cylinder engine?

    I've never done this before, and undertook it for the first time today, guided by books, google, and YouTube. My truck's a 4 cylinder. I did the first test after driving it for a while to warm it up. I got 150-150-146-140 psi for the four respective cylinders 1-2-3-4. The instruction I was...
  25. marellasunny

    Damper energy absorption during rebound is different from compression

    I understand that the purpose of a damper system is to stop the spring from bouncing during rebound. But,technically speaking,I do not understand the matter of energy absorption in the damper during rebound. 1.The damper is absorbing energy during compression along the bump and dissipating...
  26. G

    Thermodynamics - Adiabatic Compression

    A monatomic ideal gas that is initially at a pressure of 1.60×105Pa and with a volume of 8.50×10−2m3 is compressed adiabatically to a volume of 4.00×10−2m3 A) What is the final pressure? - 5.63E5 B) How much work is done by the gas during the compression? C) What is the ratio of the...
  27. S

    Linear Relationship b/w Spring Compression and Projectile Distance?

    I have a question about a spring gun. Suppose the barrel of a spring gun is placed horizontally at the edge of a horizontal table. You put say a marble in the barrel and compress the spring x cm and after releasing the marble it travels a horizontal distance of y cm before hitting the floor (so...
  28. T

    Compression of a spring. Hooke's Law vs. Conservation of Energy

    Homework Statement Lets say I have a spring with a stiffness of k = 250 N/m originally unstretched. I then gently place a 5 kg block on top of the spring. How much does the spring compress? Homework Equations W = mg F = -ks mgΔh = 0.5k(Δh)2 The Attempt at a Solution Using...
  29. O

    Understanding Z-Field Compression: A Beginner's Guide

    Hello everyone, I know nothing about physics - i can barely spell the word. I am curious if anyone can explain to me what z-field compression is? I think its related to black holes? Much appreciated
  30. M

    Bending pipe - compression and tension

    Hi, I'm a bit confused. Say you're bending a cylindrical pipe (tube, hollow cylinder). So the neutral axis of the pipe will be in the middle of the pipe and all the material on the inside of the bend (to one side of the neutral axis) will be in compression, while all the material on the...
  31. E

    Compression strength measurement

    Hello all, I have to measure the compression strength of a porous ceramic body (d=L=10 mm) using advanced force gauge, mecmesin and don't have any experience with it. The simple procedure, which I followed, was to measure the force at which the sample started to break, divided by the cross...
  32. B

    Maximum compression of the spring

    Homework Statement Mass- 0.8 kg Initial Velocity- 3 m/s Spring constant- 500 N/m No friccion Final velocity- 0 Homework Equations What is the maximum compression of the spring? I don't know where or how to start! Please help.
  33. crador

    Compression of air entrained in water

    Hello! I am wondering what supplies the energy necessary for the compression of a gas that is entrained in a flow of water. For example: 1. a water/air mix is traveling down a horizontal pipe with some speed v. The pipe enlargens and thus waterspeed falls and static pressure rises. The...
  34. S

    Calculating Spring Compression for Stone Sliding Down Hill

    Homework Statement A 15.0kg stone slides down a snow-covered hill, leaving point A with a speed of 12.0m/s . There is no friction on the hill between points A and B, but there is friction on the level ground at the bottom of the hill, between B and the wall. After entering the rough...
  35. R

    Understanding Nitrogen Compression: Implications on Pressure Vessel Design

    Hello, I am currently designing a pressure vessel and am interested in compressing it with nitrogen up to approximately 10 MPa. How would I go about determining the associated temperature rise when this takes place? This will have implications on the strength of the metal used. Thank you...
  36. H

    Ideal diatomic gas undergoing adiabatic compression

    Homework Statement A very simple question, but I can't figure it out. An ideal diatomic gas, with rotation but no oscillation, undergoes an adiabatic compression. Its initial pressure and volume are 1.20 atm and 0.200 m^3. Its final pressure is 3.60 atm. How much work is done by the gas...
  37. EVriderDK

    Refrigeration theory: Why does the compression follow an isentrope?

    When you have a perfect compressor the compression will follow an isentropic line and an h,log(p)-diragram (enthalpy,pressure diagram) but why? What is entropy exactly and what does it mean in such a system? In real life the compressors have an isentropic efficiency of maybe 0.8, which will...
  38. M

    What is the physical difference between compression waves and longitud

    Hello, this is my first post on this forum so nice to be here, and I'll be very appreciative of any responses. My background is in acoustics, and hence my question is relevant to vibration propagation. The terms 'compression' and 'longitudinal' are both frequently used to describe the same...
  39. I

    Compress Methane Safely Without Risk of Explosion - Sam

    How can i compress methane without a risk of it exploding? I want to compress methane generated form biomass into a storage tank (a small propane tank) without flattening my workshop. Does anyone know a safe way to do this? Thank Sam
  40. M

    Maximum Compression and Velocity of Spring-mass System

    Hey guys If I have a cylinder of mass 5 kg and release it along the vertical axis onto a spring with stiffness coefficient (k = 1.8 kN), how would I need to set up the work/energy equation(s) to find the maximum compression and deflection of the spring. And what would the maximum velocity...
  41. E

    What is the maximum compression of the spring xmax during the collisio

    Homework Statement A 4.80kg cart has a spring with spring constant 3200N/m attached to its front, parallel to the ground. This cart rolls at 4.40m/s toward a stationary cart with mass 1.60kg . Homework Equations PEspiring = 1/2*kx^2 KE = 1/2*mv^2 The Attempt at a Solution I was...
  42. S

    Thermodynamics - Isentropic Compression

    Hello all, Its review time again for another Thermodynamics midterm. As such, I have a practice exam to try for optional extra review work. I've come across a problem that I'm somewhat stumped on. I've tried the problem, but I feel as though I've made too many assumptions in trying to solve...
  43. L

    Arch Bridge Compression Calculations - Help

    Hi all, basically we're building a model bridge (30 grams) for a mechanical engineering project out of balsa wood and kevlar (for the strings). I've attatched a pdf file of the bridge design, although it doesn't show the strings. We are wanting to do some basic load compression calculations...
  44. B

    Does the Adiabatic Gas Equation Apply to Liquid Compression at High Pressures?

    Hi all, Hope you can help I am trying to figure out the temperature rise in a liquid subject to high pressures (7000bar in this case) Is the below adiabatic gas equation still suitable? or is there another way of working this out for liquids? T2 = T1(v1/v2)^y-1 P2 = P1(v1/v2)^y Were y =...
  45. N

    Spring compression homework problem

    Homework Statement A 165g plastic block is set up against a spring. The block rests on a smooth (I'm assuming this implies that there is no friction involved) horizontal surface. The block is pushed into the spring, compressing it a distance of 15.0 cm and released. The spring constant is k=...
  46. H

    Gas liquefaction through compression

    This is more a thought experiment that I'm not completely sure I'm getting correctly... So here we go: Imagine we have a tank that we are filling up with a substance in gaseous form. Imagine also that we have a good pump that will allow us to fill this tank with this gas up to very high...
  47. S

    Non-Quasistatic Compression

    Homework Statement A cylinder contains one liter of air and room temperature (300 K) and atmospheric pressure (105 N/m2). At one end of the cylinder is a massless piston, whose surface area is 0.01m2. Suppose that you push the piston in VERY suddenly, exerting 2000N. The piston moves only...
  48. H

    Relative Humidity and Dew Point after compression

    Hello all, Would appreciate some guidance here. I have an air compressor compressing ambient air to 3000 psi into a 425cu-in tank. I have the volumetric flow rate at the exit. If I was looking for relative humidity, dew point, and moisture content/accumulation at the exit, how would I go...
  49. Z

    Compression of an ideal gas

    Homework Statement An ideal gas, Cp = (5/2)R, Cv = (3/2)R, is changed from P1 = 1 Bar and V1t = 12m^3 and V2t = 1m^3 by the following mechanically reversible processes: a) Isothermal compression b) Adiabatic compression followed by cooling at constant temperature c) Adiabatic compression...
  50. S

    Fuel that doesnt need compression?

    Excuse the language. English is not my first language and in physics terms I might be lacking. I was just brainstorming. Is there a fuel that could be used with efficiancy in a compression free engine?
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