What is Measurements: Definition and 394 Discussions

Measurement is the quantification of attributes of an object or event, which can be used to compare with other objects or events. The scope and application of measurement are dependent on the context and discipline. In natural sciences and engineering, measurements do not apply to nominal properties of objects or events, which is consistent with the guidelines of the International vocabulary of metrology published by the International Bureau of Weights and Measures. However, in other fields such as statistics as well as the social and behavioural sciences, measurements can have multiple levels, which would include nominal, ordinal, interval and ratio scales.Measurement is a cornerstone of trade, science, technology and quantitative research in many disciplines. Historically, many measurement systems existed for the varied fields of human existence to facilitate comparisons in these fields. Often these were achieved by local agreements between trading partners or collaborators. Since the 18th century, developments progressed towards unifying, widely accepted standards that resulted in the modern International System of Units (SI). This system reduces all physical measurements to a mathematical combination of seven base units. The science of measurement is pursued in the field of metrology.

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  1. M

    I Behavior of successive measurements

    [Mentors' note: Split off from this thread as it was a digression there] After you make a measurement and find the particle to be in a particular eigenstate, if you measure that particle again will you find it to be in that same eigenstate?
  2. B

    Spin measurements of an electron

    Homework Statement Consider an electron described initially by ##\psi = \frac{1}{\sqrt{10}} \begin{pmatrix} 1\\ 3 \end{pmatrix}##. A measurement of the spin component along a certain axis, described by an operator ##\hat{A}##, has the eigenvalues ##\pm \frac{\hbar}{2}## as possible outcomes (as...
  3. O

    B Entanglement measurements timing

    I have a trivial question: when measuring 2 entangled particles A and B, what should be the timing between the measurments to get correct results? In other words after measuring A how long can we wait before measuring B before its state changes?
  4. J

    I Comparing Electric Field Intensity in Moving Systems F & F

    Imagine that we have an intertial system F, and there is an electric charge Q at the origin. Obviously the field is symmetric and spherical in this reference system. Imagine another inertial system F' that is moving at constant speed v to the right respect to F, and at t=t'=0 both origins...
  5. G

    I Commuting observables vs. exchanging measurements

    Hi. I'm afraid I might just be discovering quite a big misunderstanding of mine concerning the meaning of the expectation value of a commutator for a given state. I somehow thought that if the expectation value of the commutator of two observables ##A, B## is zero for a given state...
  6. Diana Moceiparisi

    Uncertainty in Fluid Viscosity Measurement: Improving Result Presentation

    Homework Statement a) The equation governing the flow rate, , of a fluid under streamline conditions through a horizontal pipe of length l and radius r is: where p is the pressure difference across the pipe and ƞ is the viscosity of the fluid. Thus, a student conducted an...
  7. A. Neumaier

    I Many measurements are not covered by Born's rule

    1. Within the framework of a Hilbert space for an atom one cannot find an observable in the sense of ''self-adjoint Hermitian operator'' that would describe the measurement of the frequency of a spectral line of the atom. For the latter is given by the differences of two eigenvalues of the...
  8. hsdrop

    B Measurements within our solar system with relativity in mind

    ok I know that anybody in the heavens will bend spacetime with the gravity it has. What I was wondering was how do we measure around them like from the Earth to mars. When Mars in now quit on the opposite side of the sun ( so we can see it at sunset). do we measure the parabolic curve in...
  9. parshyaa

    B Measurements of angles in circular method

    Why θ in radian equals arc/radius? I know that it can't be proved but there must be a explanation for this formula. How founder may have got this idea.
  10. Erland

    I Everett on measurements: what does he mean?

    I am trying to read Hugh Everetts thesis about the universal wave function, which is now called the many worlds interpretation of QM. At page 53 ff. he discusses measurements. He talks about a system composed by two state functions, saying that the two subsystems can be considered as measuring...
  11. O

    The precision in measurements of radial velocities by DE?

    Hello, I have an exercise here that I need help with. The precision in measurements of radial velocities by the Doppler effect is currently 1 m/s. Can a Jupiter like planet orbiting a star similar to the Sun at a distance from the mother star equal to the Sun-Jupiter distance be detected? (Use...
  12. G

    I "Counterfactual definiteness" vs. "free will"

    Hi. What's the exact relation between the assumptions "counterfactual definiteness" and "existence of free will"? I (think I) know their "definitions" in QM: counterfactual definiteness: ability to speak meaningfully of the definiteness of the results of measurements that have not been...
  13. gasar8

    Two particles with spin - measurements

    Homework Statement We have got two particles with S_1=1 and S_2=1. We know that S_{1z}|\psi_1\rangle=\hbar |\psi_1\rangle and S_{2x}|\psi_2\rangle = \hbar |\psi_2\rangle. a) Find wave function |\psi_1\rangle in S_{1z} basis and |\psi_2\rangle in S_{2z} basis. b) We measure S^2 of total...
  14. N

    A Data Analysis: consistency of e.g. two measurements

    How do we check consistency of measured data, e.g. x1 = 1 ± 0.1 x2 = 1.4 ± 0.3 I can do this for two different samples to check for significance in terms of different means, but how to check internal consistency of a single set. How can we do this using: a) standard normal probability table...
  15. RabbitWho

    Expressing measurements in SI units

    Homework Statement I am given some measurements and I am supposed to express them as standard SI units. I can't find any examples of this done online or extra practice exercises to help me. I am probably googling the wrong words. I have been out of school for quite a while and I don't know what...
  16. F

    Kalman filter and measurements

    Hello, I am using a Kalman filter with a PI controller. The goal is to control a mirror to stabilize the position of a laser spot: I am sending a disturbance on the mirror and the PI sends command to the same mirror so the spot stays fix. With a camera I am recording the image of the laser and...
  17. F

    A How to convert between different mass measurements for CDM H

    If I have a cluster with a mass measured in M_500c, then how do I go about converting that mass to M_200c given some concentration and an NFW profile?
  18. Y

    I Radioactivity measurements -- finding a fit for lab measurements

    As a part of an experiment in radioactivity, we placed an alpha particles emitting source (Am) and a sensor in a vacuum chamber, and measured the power (number of particles per time unit) for various angles of the sensor. Our goal is to fit a theoretical function to our measurements (power vs...
  19. michael879

    A Hidden Measurements Interpretation

    I've been reading up on HMI, and the claims its proponents make are pretty impressive. I'm struggling to understand some details though, so I'm hoping someone here is more familiar with it. In http://www.vub.ac.be/CLEA/aerts/publications/1998Berlin.pdf, the authors describe a "macroscopic...
  20. Fosheimdet

    I Possible measurements of z-component of angular momentum

    I'm looking through an old exam, and don't quite understand the solution given for one of the problems. We have given a wavefunction g(\phi,\theta) = \sqrt{\frac{3}{8\pi}}(-cos(\theta) + isin(\theta)sin(\phi)) and are asked what possible measurements can be made of the z-component of the...
  21. M

    Stargazing Facing difficulties with radio telescope measurements

    Hi Me and a couple of class mates are working on our bachelor's project of which the mission is to measure the temperature of the sun using a parabolic antenna. We are having great troubles trying to come up with an equation relating the antenna temperature (which we are able to calculate with...
  22. M

    A Tension between local and CMB measurements of Hubble constant

    "A 2.4% Determination of the Local Value of the Hubble Constant" by Riess et al has led to some excited news stories recently. I don't see it discussed anywhere here. Looking for the essence of the paper, I note three things: The two measurements considered are "the Hubble constant ... measured...
  23. A

    Uncertainty in Measurements: Understanding Multiplication Factors

    Hello, guys! (And girls, but.. you know..) There are several things I do not quite understand, so, can you help me clear my doubts? ^^ 1) How do I know when to multiply the value of calculated data when it comes to determining the uncertainty of the data? 2) When do I multiply the percentage...
  24. O

    Hall Effect Measurements and Analysis

    Hi all, I am reading about hall effect measurements and analysis from an old physics book, A. C. Melissinos, Experiments in Modern Physics, for a lab class I'm taking. An experiment involving hall and resistivity measurements of a p-type germanium sample is performed and discussed. He notes...
  25. M

    Approximate a spectrum from a series of measurements

    Hi. I am working on a linear algebra problem that arose somewhat like this: Suppose that you are shining a light with a known intensity spectrum P(\lambda) upon a surface with an unknown reflection spectrum, R(\lambda). You have a detector to detect the total reflected light intensity, I. How to...
  26. F

    Exploring Wind Tunnel Data Collection Methods for Physics Coursework

    I'm nearly at the end of my preliminary testing for a wind tunnel in my A2 physics coursework. My question for my project so far is: "Do different shaped objects exhibit different properties under the influence of high speed air". For my coursework I need to measure or observe something to get a...
  27. Zafa Pi

    Mathematical and actual measurements?

    Let me introduce notation so my question makes sense. A set of orthogonal states can be distinguished by a Q-measurement, e.g. |0> and |1> (Q-computation notation) can be distinguished by measuring with the observable Z which has eigenvectors |0> and |1> with eigenvalues +1 and -1. But if those...
  28. T

    Does the Mass of an Accelerometer Affect Vibration Frequency?

    Hi everyone, Is it normal if the acceleration measured is different with different instrumentation? I have measured the acceleration of shaker with three different accelerometer and I didn't obtain the same result. Thanks for your help!
  29. C

    Exclusive measurements at the lhc

    I am just wondering if someone could tell me what 'a higher order QCD calculation relevant for exclusive measurements at the lhc' means? In particular, what is an exclusive measurement and are such QCD calculations done on the lattice or is it perturbative analysis? Is there something special...
  30. U

    Do Moving Objects Return to Original Length After Stopping?

    Not long ago a very thoughtful thread cleared my mind on the Relativity of Simultaneity. I am very thankful and hope to get here help also on a question related to the RELATIVITY OF MEASUREMENTS in the moving reference frames. Suppose that innumerous bars (or rods) are loaded on a very long...
  31. K

    Did Lord Kelvin Say "If You Can't Measure It, It Isn't Real!"?

    The other day, in conversation, I attributed the dictum, "If you can't measure it, it isn't real!" to Lord Kelvin. However, when I chanced to look it up in Wiki, I could find no confirmation of this attribution. Was I mistaken? Did Lord Kelvin ever say anything to this effect? If not, is...
  32. RJLiberator

    Quantum Measurements: The Average value is the cosine

    Homework Statement We know: In a measurement of quantum mechanics (basic) the average value is the cosine of the angle between the orthonormal basis of the measurement apparatus and the qubit (vector) entering it. Question: How do we prove this?Homework EquationsThe Attempt at a Solution Can...
  33. RJLiberator

    Qubit Probabilities and Angles between the measurements

    Homework Statement Suppose that two measurements are made on a qubit in rapid succession. The first is δz and the second is δn. Suppose the first results is always +1. Calculate the probabilities of obtaining the results +/- 1 for the second measurement in terms of the angle θ between z and n...
  34. E

    Advancements in Kilogram Measurement through Silicon and Watt Balance Technology

    What is the point of new measurements of kg, by ##Si^{28}## ball and with Watt balance? Is it this a special moment because Avogadro numbers, ##N_A##, of both measurements agree? What values of ##N_A## were given by both measurements and what values of ##N_A## were before these measurements? I...
  35. R

    Multiple Measurements of a single Qubit

    Hi :-) I'm working on my master thesis in the field of quantum theory; currently I investigante No-Go-Theorems like the No-Cloning, No-Deleting, No-Hiding, No-Communication-Theorems ans so on. There is a fundamental question which is somehow linked to the No-Communication-Theorem. Is it - in...
  36. S

    Exploring Weight Measurements in Water Experiments

    Homework Statement I place a water filled beaker on an electronic balance and zero the reading. Meaning the balance will not be measuring the weight of the water and the beaker. a.) If a ball is resting at the bottom of the beaker. What would the balance be measuring? b.) If I immersed and...
  37. B

    High Temperature electrochemical measurements

    Hi all, I'm interested in high temperature sample holders of electrochemical measurements especially for Li-ion batteries. But I couldn't find one. Does anyone use it before? Best regards
  38. G

    Practical measurements of ramjet engine

    Hello everyone I am trying to design a ramjet engine. For that I need measurements of its parts. Does anyone know how to calculate them or have a link to a website where I could find more information?
  39. Tone L

    What instruments can measure electron density in the ionosphere?

    Is there an instrument or has there been an instrument that measures electron density in the ionosphere (50km - 450km)?
  40. T

    Distance measurements with two cameras

    Hello, I would like to know if there are simple ways (using trigonometric functions) to calculate distances between an object and two cameras. I am using two CMUcam5 (pixy), closely placed (the distance between the two cameras is known). And I would like to calculate the distance between the...
  41. Ken G

    I Modeling of measurements in relativity

    I would say there is no way to predict experimental outcomes than mathematics. But "expressing physics" can be rather different. For example, how many times have we asked ourselves, "I see that the mathematics works out this way, but I want a physical explanation." Indeed, I have found that...
  42. ChrisVer

    Combinations of measurements: obtain mean and errors

    I was looking at the attached picture, where it gives the Higgs Mass obtained from the two different channels from ATLAS and CMS. Let's only talk about the diphoton channel : H\rightarrow \gamma \gamma From the ATLAS the mass value is: m_{Ah} =126.02 \pm 0.51 and the CMS: m_{Ch} =124.70 \pm...
  43. C

    IOR Uncertainty Quantification for PIV/LDV Measurements

    Hello All, I am running some experiments using Particle Image Velocimetry and Laser Doppler Velocimetry techniques. There is a slight mismatch in the Refractive Index of the fluid and my model (Approximately 5% difference) which is creating some uncertainty in my measurements. I was wondering...
  44. T

    Question about spectral emission measurements of hydrogen

    Looking for typical experimental parameters for measuring emission spectrum of both H and H2, specifically gas pressures. Also would like to know typical pressure range where spectrum transitions from H2 to H. Thanks.
  45. G

    Planck Measurements: Meaning or Trite Observation?

    Does anyone here ascribe any particular broader meaning to them? Is that they represent indivisible units a consensus of sorts? Do they have real meaning or are they a kind of trite observation?
  46. slitted

    Hiding the observer with gravitational measurements?

    Hello again. In a double slit experiment with electrons, suppose that we have the instrumentation to measure how space-time is curved by these particles. Would it be possible to obtain the electron's position and momentum by measuring the change in the direction of photons that move nearby but...
  47. M

    Calculating average from probabilistic measurements?

    I have got a sample size of 1000 and I calculated the mean probability of success of an event by breaking this sample size into sets of 50 and also have the standard deviation and standard error of mean of this success. Now I repeat this process and have another set of data. What will be the...
  48. C

    Interpretation of Accelerometer Measurements

    I have performed an impact test on different football shin guards to assess their performance. I am however confused with the readings measured by the accelerometer I have used. The sensor was attached to a striking mass of 4.3 kg which was dropped at different heights. The graph I have attached...
  49. J

    Entanglement, Measurements, and Interactions

    Hello, I'm trying to better understand entanglement in the context of measurements and interactions. (1.) Are uncertainty and entanglement linked together? Are the eigenstates of an observable entangled since a measurement of one of them collapses the wavefunction to a single eigenstate, making...
  50. Dadface

    Precision measurements of atomic mass.

    Hello I have been trying to find out how the data for the atomic mass of different isotopes is processed. I am vaguely familiar with mass spectrometry and other techniques used for the measurements and I know that the experimental results are coordinated by the Atomic Mass Data Centre. I am...
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