What is Measurement: Definition and 1000 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. C

    How can I differentiate between alpha particles and helium in an enclosed space?

    Can someone recommend (if possible) a way to detect the amount of helium in a given enclosed space? I'm designing an experiment in which I will need to measure the amount in an otherwise vacuum.
  2. A

    Distance role in simultaneity measurement

    Thanks for the answers on my previous thread, it made some sense, and if I'll reply if there's further misconception. My new question is quite connected to the famous Andromeda paradox. So it's stated that the Andromeda is far away and moving towards the galaxy will cause the observer to have...
  3. U

    Possible measurement, eigenvalues of eigenfunctions and probabilities

    Homework Statement Suppose the angular wavefunction is ##\propto (\sqrt{2} cos(\theta) + sin (\theta) e^{-i\phi} - sin (\theta) e^{i\phi})##, find possible results of measurement of: (a) ##\hat {L^2}## (b)##\hat {L_z}## and their respective probabilities. Homework Equations...
  4. jk22

    Measurement, information and entropy

    If we have a qubit in a mixed state, let say 1/2(+><+)+1/2(-><-) and we measure it. Is then the result a pure state + or - ? If this is the case, then the entropy of the system decreases. Now the question another way round is : Suppose we measure a quantum system without gaining...
  5. B

    Vector current and its measurement

    An electrocardigram measures the electrical current in the heart by using several "leads". These leads have +ve and -ve ends. http://www.heartaxis.com/ If you take a look at the interactive FLASH about 1/4 of the way down the page (yellow arrow and green line ppd to each other) and the...
  6. S

    Exploring the Concept of Time: From Cesium Atoms to Atomic Clocks and Beyond

    According to "Physics for Engineers and Scientists by Ohanian and Markert, a second is the time needed for 9,192,631,770 vibrations of a cesium atom. In 1971, Hafele and Keating put four cesium-beam atomic clocks aboard commercial air liners which were flown around the world - two eastward...
  7. P

    Is Uncertainty intrinsic property or a consequence of measurement ?

    Hello friends, Most people that I heard put uncertainty as an intrinsic property of the universe which is evident when we make a measurement. But to me it seems that intrinsic property and making a measurement are two entirely different things. If uncertainty were to be just(purely)...
  8. D

    Double slit with time measurement

    Propose this measurement: It is a well know interference measurement, but now asymmetrical. Suppose the red path is 1 m and the blue path 10 m. If you measure the time between detector 1 and 2 I expect you will find two times: 3.3 ns and 33 ns. Then you know which path the photon took...
  9. S

    Expectation value for a position measurement

    Homework Statement Given the wave function psi(x,0) = 3/5 sqrt(2/L) sin(xpi/L) + 4/5 sqrt(2/L) sin(5xpi/L) in an infinite potential well from 0 to L, what is the expectation value <x> and rms spread delta E = sqrt(<E^2>-<E>^2) Homework Equations <x> = integral from 0 to L of psi*xpsi dx...
  10. M

    Quantum Physics and Lack of Measurement

    So this semester our lecture explained and showed us the double slit experiment. And it he explained to us the uncertainty principal that the act of observation can change the result. However this is the part where I kind of a have a problem with.. Since quantum physics is based on the...
  11. S

    Measuring Ocean Waves for Wave Energy Projects

    Halo everyone. I am new to here! I am working with a project of ocean wave energy. I would like have a device that can measure the wave length, pitch those wave parameter when I testing my wave energy device. Anyone have a clue what kind of device can complete my task?
  12. S

    Hydrogen wave function in terms of m_z after m_y measurement

    Homework Statement Given the following wave function for hydrogen: psi(r, t=0) = (1/sqrt(10))*(2*psi_100 - psi_210 + sqrt(2)*psi_211 + sqrt(3)*psi_21(-1)) where the subscripts show n, l, m_z, respectively, and the psi_nlm_z are already normalized. - At t=0, we measure and find l = 1...
  13. T

    Why does the wave function have to collapse upon measurement?

    How does the Copenhagen interpretation motivate its claim that the wave function of a quantum system collapses when a property of the system is being measured? I mean, was there some problem they were trying to solve by introducing the notion of wave function collapse? What would happen if the...
  14. T

    I need some tips about a Gauss measurement

    What can a gaussmeter tell me about a metal? I am just experimenting with various metal disc samples by setting them on the Hall probe of a gaussmeter. I have the meter zeroed out, then I pace the metal on the probe. The metals all effect the field measurement in different ways, but I...
  15. atyy

    Simultaneous measurement of noncommuting observables

    It is often said that non-commuting observables cannot be simultaneously and precisely measured. The rough idea is that the procedures to measure each observable are different. Is the statement strictly correct? If so, what is the mathematical argument? Is it possible to use Ozawa's...
  16. F

    Total Harmonic Distortion, THN measurement

    I have a couple of questions about what total harmonic distortion is, and what the measurement means. The definition I've read most places is: \frac{D}{S} × 100% , where S is the amplitude of the fundamental frequency, and D is the amplitude of the sum of all of the harmonics. A common...
  17. DaTario

    Neon Lamp Polarity Measurement

    Hi All, I would like to know why the neon lamp is used to measure electrical polarity. What is the working mechanism involved. Best wishes, DaTario
  18. E

    Irradiance measurement procedure

    Here's what I'm thinking. The sun is too bright to measure directly with our equipment. If I calibrate without a filter, and capture the reference spectrum with and without the filter, then I can model how the filter changes the spectrum. This way I can capture the sun spectrum with the filter...
  19. G

    How to show that cloning by measurement is impossible?

    Hi, I know the common proof of the no-cloning theorem assuming the cloning apparatus acts unitarily on the system and leading this to a contradiction. But what about a non-unitarian apparatus that involves measurements? I'm pretty sure cloning is still impossible, but I don't know how to...
  20. M

    Sound Waves length measurement

    Homework Statement Two sources, A and B, emit a sound of a certain wavelength. The sound emitted from both sources is detected at a point away from the sources. The sound from souce A is a distance d from the observation point, whereas the sound from source B has to travel a distance of...
  21. G

    Bell experiment: Rotate measurement device 180°

    Hi, I was just writing another thread when I stumbled upon something strange: What if I now make a slight change and replace ##\bf{b}\rightarrow-\bf{b}##? The expectation values containing ##\bf{b}## change signs and I get $$\left|\frac{1}{\sqrt{2}}-0\right|=\frac{1}{\sqrt{2}}\leq...
  22. G

    Analyzing Bell's inequality for different measurement angles

    Hi, I'm trying get a better understanding of Bell's inequality in the form $$\left|E\left(\bf{a},\bf{b}\right) -E\left(\bf{a},\bf{c}\right)\right|\leq 1+E\left(\bf{b},\bf{c}\right)\enspace.$$ I'm considering the Bell state $$\left|\psi\right\rangle=...
  23. M

    Articles & Journals for Flow from Impinging Jets, Velocity Measurement

    Hello, I was wondering if anyone can recommend any good articles or journals with valid and good velocity data for flow from an impinging jet on a flat surface with an approximate Reynolds number of around 75,000 to 90,000? I have looked and seem to have lots of data for heat coefficients but...
  24. craigi

    Measurement of entangled particles causes dechorence at a distance?

    If we entangle particles and separate them by a large distance, can the action of measuring one cause decoherence at the other's location? If yes then does this violate relativisitic causality? Could we not use this process to transmit information instantaneously? If no then why not? Is there...
  25. D

    Propagation of error with sliding window of measurement

    Hello, I don't seem to know how to ask google this question so I thought I'd see if I could get an answer from here. Say I have 400 measurements of some variable. I take a sliding window of 50 events and take the standard deviation of each set of 50 events. That would be 350 measurements. Now...
  26. Q

    Question about time and measurement

    Hi PF people, I am brand new to PF and this is my first post so please excuse and help correct any mistakes I make. My question is about time, the perception of time and the units we measure it in. I figured I would start this question with a statement because if my general understanding of...
  27. A

    Lasing experiment and the measurement of intensity

    I have just completed an experiment on principles of lasing, constructing a laser and measuring the beams intensity distribution. This distribution of the beam was measured using a detector mounted on a traveling microscope. The detector had a pinhole cover such that only a small fraction of the...
  28. E

    Metric VS English engineering system of measurement

    Hey guys, I know you all wish you never had to do all the weird conversions required for our current system of measurement. I know I'd rather convert 17km to m than 17mi to feet or ever inches. I thought that since I know so many people who would rather just do the easy metric conversions...
  29. K

    Measurement of concentricity using CMM

    Hello, If I want to measure the concentricity of a cylinder with another, is it possible using a CMM? If yes, can you pl. explain me the procedure? I have read that concnetricity has to be measured based on the mid point of a diameter-line of a cylinder. This means, I have to measure the...
  30. M

    Relativity and Distance Measurement in Physics | PF Community Discussion

    Hello PF members! First of all, let me start off my post by admitting that I have created a duplicate account. My original account was banned for a good reason. Now, I am studying physics. More specifically, I'm studying relativity. I trust that you all will help me understand what...
  31. A

    Can we look upon entanglement as measurement?

    Hi, I have a question about how to interpret the state of an entangled photon H = horisontal, V = vertical polarization The global state is |Phi> = (|H>|V> + |V>|H>)/sqrt2. By density operator formalism: rho = |Phi><Phi| = (1/2) ( |H>|V><H|<V| + |H>|V><V|<H| + |V>|H><H|<V|...
  32. S

    Can we trust our measurements in cosmology?

    Morning everyone, We know of some illusions in our everyday experience, such as an echo making us believe someone is talking back at us, or mirages in the desert, or mirrors making us think there are two symmetric objects when one is only the reflection of another. I was wondering about...
  33. N

    Measurement of power associated witha vertical shaft

    How can I measure the power associated with a vertical rotating shaft (similar to the shaft of a vertical axis wind turbine). power=Torque*angular velocity Angular velocity can be found by using tacho meter or spectroscope.. but i am confused how to measure the torque...
  34. M

    Gyroscope Measurement and Angular Rates

    Do gyroscopes give the angular rates about its local axes or about a frame that is fixed and initially coincides with its local frame? I mean: would this sensor give the rate of change of the Euler's angles or the angular velocity ω (about the inertial frame)? One more question: I know that...
  35. Q

    Simultaneous measurement of entanglement

    Im not sure if there are any implications to be made, but it struck me as interesting as what would happen if measurements of the same parameter were simultaneously made on each of two entangled particles? Can anyone speak to this perchance?
  36. R

    What methods are used to measure cosmic distances?

    How do astronomers measure cosmic distance, say 7 billion light-years? http://www.space.com/17399-gamma-ray-photons-quantum-spacetime.html
  37. F

    Flow measurement in venturi meter

    First I am trying to find the theoretical flow rate but I am not able to get the answer because since diameter of the pipe is 0.03m throughout, when I sub into the formula: My A1/A2 will be 1, and 1-1 = 0. And I will get maths error whatever is divided by 0. Am I going in the wrong direction...
  38. J

    Building a measurement system based on C

    I always try to assume that pretty much anything I think of has been thought of before, so I am relatively sure that this is also not a new question. we base our current measurement systems on arbitrary lengths such as the meter or foot, etc. there are certain applications where we use...
  39. A

    Quantum Measurement: Collapse, Reduction, Decoherence, Weak & Strong Projection

    what is differences between collapse,reduction, decoherence , weak projection and strong projection in quantum measurement theories?
  40. S

    Measurement in special relativity

    hi I read this statement in site www.askamathematician.com and I couldn't understand it. is it possible to explain this? "if measurements A and B are taken enough apart, they will be “space-like separated” according to SR, meaning that neither event precedes the other. Some observers will...
  41. M

    Estimating measurement error using error from linear regression

    Sorry if I'm in the wrong subforum. This is a rather simple and straightforward question, I hope. I'm doing a measurement that requires me to do a linear regression on data points to get a value of the slope. The slope is the value of the actual property that I am measuring. Assuming...
  42. S

    Question about Entanglement and Measurement

    I want to ask a question regarding how spin state of an electron becomes entangled with the slit an electron travels through in the double slit experiment. So I understand that in the double slit experiment, we have two slits 1 and 2. We place a detector by slit 1 to measure whether or not...
  43. H

    Measurement of upward force exerted by a human on a vertical jump?

    Hi, I'm doing some research on developing a physics-based platform game and I want to see how the gameplay will feel if the environment and physics were made to scale as realistically as possible. Since one of the core features of a 2D platformer is jumping, I need some figures on how much...
  44. E

    Measurement uncertainty and error

    Suppose we have x plates of wood of thickness (0.0150 \pm 0.0002) \text{ m} and we wish to stack them into a pile of height (1.000 \pm 0.001) \text{ m}. The number of plates x required is then x = \dfrac {1.000 \pm 0.001}{0.0150 \pm 0.0002} \, . How many plates will certainly fit in the...
  45. M

    Why is My 240v Line Voltage Only Measuring 16v Between Line Phases?

    why am I only getting 16v between both line phases coming into my service from the meter on a 240v single phase panel for a home
  46. A

    Solving Length Measurement in Homework Problem

    Homework Statement I am having a hard time understanding the length measurement in the problem. We went over this example in class and the length, L, was something I didn't realize until now. Question: A 6-ft-long steam pipe is made of A-36 steel with σ=40 ksi (yield stress). It is...
  47. J

    Quantum Zeno effect for position measurement

    Hello, The quantum zeno effect is well understood and experimentally confirmed as regards polarization measurements (as discussed here). It's the quantum analogue of "the watched pot never boils" as it allows "continuous" measurement to inhibit certain state evolutions. Does the effect...
  48. coktail

    Uncertainty Principal: Limit of measurement, or the nature of things

    Hi! I found a few old threads lying around regarding this, such as this one, but I thought I'd start a new one asking the question in my own way. So here goes. Is the uncertainty described by the Uncertainty Principal a result of the fact that by measuring something we affect it, or a...
  49. M

    Relation between actual measurement and Mathematical observables

    I'm having a gap in understanding the relation between them, and resolving my confusion is really appreciated. For example, the Hamiltonian operator, why do we call its eigenvalues energies? how do we actually measure it in the laboratory, quantum mechanically? And maybe I need a better...
  50. G

    Time 'measurement' (or definition) for early universe

    We define time by the rate at which physical processes (i.e. clocks) tick. With atoms for example we can define time by their energy transition rates such as in atomic clocks. But, what before atoms existed? Current cosmology theories make statements such as that '0.5 seconds after the Big...
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