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. L

    Uncertainty For Multiple Measurements

    Homework Statement We needed to measure the temperature of a bucket of water using a thermometer which can be read to 0.1°C. Each group would do a single measurement, the data from five groups (including our own) was to be averaged with the uncertainty stated. The data collected was: 19.5...
  2. C

    Determine type of semiconductor from IV measurements of Schottky

    I was wondering if it would be possible to determine if a Schottky diode was n-type of p-type (in the bulk) by only using I-V measurements?
  3. M

    Preparing a spin state and measurements

    Hey guys, I'm very new to quantum mechanics and have purchased 'Quantum Mechanics: The Theoretical Minimum. I'm still a bit confused by a fairly fundamental idea. In the book, it states that you first prepare a spin state (say the σz = +1) in the initial measurement. If you rotate the...
  4. G

    Does accuracy increase with repeated measurements and why

    For example, I weigh a pebble and get a value of 7.1g. Then I measure again and get 7.6g, then again and get 6.9g.. Then I repeat the measurement using the same scale 5000 times. (its just a thought experiment). Is the mean of all measurements closer to the true value and if so, why? thanks
  5. S

    Measuring the Movement of the Stars

    I was wondering, since the Earth is constantly moving around the sun, the sun is moving around the milky way, and the milky way is moving through space (and for all I know the milky way might also be rotating around our local group, cluster, super cluster, etc.), how do we know how fast...
  6. J

    How to calculate error propagation for several measurements?

    I'm having trouble with error propagation analysis. When you make a single measurement of several variables, say (x,y,z) and you calculate a function f(x,y,z), you just have to apply the common formula of error propagation: $$\sigma_f(x,y,z)=\sqrt{\left| \frac{\partial f}{\partial x} \right|...
  7. 9

    Two measurements from different sources - how to combine?

    I can get a measurement of my distance between points (x1,y1,z1 and x2,y2,z2) by analysing position data from a GPS/barometer system, which has a standard deviation of about 2m for x y z positions. I can also analyse data from a system that provides velocity with a standard deviation of about...
  8. A

    Total Angular Momentum Measurements

    Homework Statement Consider a particle with orbital momentum ##l=1## and spin ##s = 1/2## to be in the state described by $$\Psi = \frac{1}{\sqrt{5}}| 1,1\rangle|\downarrow\rangle+\frac{2}{\sqrt{5}}|1,0\rangle|\uparrow\rangle$$ If the total angular momentum is measured what would be the...
  9. C

    MHB Calculating Height of RC Glider from Ground and Air Measurements

    Hello,just seeing if someone can help me on here,i have a rc glider measuring 2200 mm on the ground,when in the air it measures about 35mm. Can the the height be calculated from these measurements.
  10. E

    Ship Mounted Coilgun Measurements

    In the story I am currently working on, a weapon commonly used on ships is a sort of coilgun. I want to create a ratings system for these coilguns and want to know the range of ampule-turns that would be used in large coilguns (barrel diameters range from six inches to two feet).
  11. E

    Rounding uncertainties and measurements

    Hello, I have some questions on uncertainties in measurement: Say you have a ruler with 1mm graduations, and you are trying to measure the length of a metal rod. One end of the metal rod is at the 120.0mm graduation, and the other is in between the 19 and 20mm graduation, and you approximate...
  12. CassiopeiaA

    RMS value & noise measurements

    I am confused about very fundamental question. Why does the rms value of number of electrons collected from a signal(like in photoconductor) gives you the noise in that signal.
  13. Demystifier

    What is the true meaning of weak measurements in quantum mechanics?

    Here I criticize the whole concept of weak measurements and weak values in quantum mechanics, first proposed by Aharonov, Albert and Vaidman: http://prola.aps.org/abstract/PRL/v60/i14/p1351_1 1. By a suitable choice of the post-selected state, the weak value can be made ARBITRARILY large. In...
  14. P

    Combining three measurements of same thing to find error

    Hi All, So here is an error analysis question for you all: I am measuring the temperature of an object at three positions simultaneously. They are type K thermocouples so their individual error is 0.75% of their reading. However, I can also take long term data which shows that...
  15. T

    Help with high frequency measurements

    Hello everyone! So I am currently working on a project involving classroom equipment from PASCO. (http://www.pasco.com/prodCatalog/WA/WA-9314_microwave-optics-basic-system/#overviewTab) What I'm working on is not exactly related to the the classroom project but closely related to the...
  16. C

    MHB How do you add and subtract measurements?

    How would you figure a problem like this- 9' - 6 11/16 +17' - 9 3/4 I'm trying to reteach my self this math, and I can't remember how this is done. Please help asap!
  17. V

    Laser light vs. synchrotron light in ARPES measurements

    In ARPES measurements, people say that the laser light cannot cover a wide area of momentum space whereas the synchrotron light can (M. Hashimoto et al., Nat. Phys. 10 (2014) 483). Why is that? (Figure 3a in the paper is a combination of laser and synchrotron data to plot spectra along the...
  18. J

    Isolated Analog Voltage Measurements

    Hello All, I'm working on a design for a board that will allow me to plug in a standard 10x scope probe and then reduce and isolate the signal to go into the input of an ADC in a microcontroller (0-5V range) with a max bandwidth of 100 kHz. I have been shopping around for a while looking at...
  19. M

    Measurements and wavefunction collapse.

    Hey everyone.I have a couple of question regarding wave function collapse. I can accept that one cannot make a measurement with absolute precision and have a usable wave function afterwards due to the uncertainty principle... Consider a particle moving along the x-axis with a wave function...
  20. FlexGunship

    Can dark matter skew Earth-based gravitational measurements?

    I'll be cautious in asking my my question because I'm out of familiar territory. But... Given the following: that dark matter interacts with baryonic matter (exclusively?) via gravity, that evidence for dark matter shows that it exists largely near baryonic matter, and we are (almost?)...
  21. H

    Problem about taking measurements in flat metric spaces

    Hello, I am having a problem about the nature of the measurements of the intervals ds's forming out of infinitesimal displacements dx's of the coordinates and the actual meaning of the measurements of the same dx's, in flat metric spaces. I am certain that this must be a trivial problem...
  22. J

    Our attempts at certainty (measurements) actually increase uncertainty

    Here is my theory: - The measurement of an observable by an observer is a thermodynamically irreversible process. All thermodynamically irreversible processes increase total system entropy. - Landauer's principle (which was experimentally shown in 2012) says that the minimum amount of energy...
  23. R

    What is Nc in the R Ratio formula? re CDF detector measurements

    Ive attached the R ratio formula to this post, please could someone who is familiar with it tell me what Nc is? Does it relate at all to centre of mass energy? Thanks in advance for any help. source...
  24. B

    Photoelectric Detector and Energy Measurements

    Homework Statement Which of the following best summarizes how a photoelectric detector provides an energy measurement: Answer choices: A) As light of multiple colors falls on the detector, the detector measures the energy of just one frequency of light by having a hole of only one...
  25. M

    Retro causation in weak measurements?

    Hello, I have been working for a while in weak measurements and I have noticed that some physicists such as Aharonov, Vaidmenn or Popescu have suggested that weak measurements reveal some sort of retro causation phenomena. One of the things that confuse me is that they state that when we weakly...
  26. atyy

    Sequential measurements of conjugate observables

    There is an argument that accurate sequential measurement of conjugate observables A and B on the same state is possible if the state is an eigenstate of one of the observables. When the state is an eigenstate of A, an accurate measurement of A will not disturb the state, so B can then be...
  27. O

    Experimental Measurements in Wind Tunnel

    Hello everyone, the forum looks great and I have been reading it for a long time, but I have only registered. I am writing this post because I have to analyse two flow fields in a wind tunnel. 1) The first flow is generated from a helicopter blade, with Re=2000000, Mach=0.92 and...
  28. carllacan

    Role of future measurements on Bayes Filter

    This is a hard to explain question. If what I wrote makes no sense to you please let me know so that I can fix it. Suppose a zone where the weather changes like a Markov chain between sunny, cloudy and rainy. You can't observe it directly, but you have a sensor that gives some information...
  29. B

    Stern Gerlach and Position Measurements

    Homework Statement Given the following stern-gerlach setup, find the probabilities for particles to arrive in detectors D1 and D2. SGx = Stern Gerlach in x direction, SGx = Stern Gerlach in z direction (sorry for terrible ascii drawing) |ψ> = a|+> + b|->, |ψ> is normalized. ..../D1...
  30. T

    Estimating upper bound from measurements with uncertainties

    Hello everyone, I have a large number of measurements with associated uncertainties, and I know that the real values are bounded above by some constant. How can I estimate the value of that constant, and the uncertainty on the estimate? Thanks
  31. A

    Recent measurements suggest the universe it is flat and infinite

    http://www.space.com...map-aas223.html Recent measurements suggest the universe it is flat and infinite The new results, presented by Schlegel and his colleagues here today (Jan. 8) at the 223rd meeting of the American Astronomical Society, also provide one of the best-ever determinations...
  32. G

    Measurements of a superposition: Conservation laws?

    Hi, Assume we have a source that emits several copies of the same quantum state which is a superposition of several eigenstates of the Hamilton operator with different energies. We can calculate the expectation value of the energy of this state and therefore also the energy the source...
  33. H

    Can heisenberg uncertainty principle be beaten by fast measurements?

    I don't know much about physics but just had this idea: As I understand it the HUP prevents good accuracy of a small object's momentum and position at the same time. Assume trying to measure the momentum and position of a single atom. In theory, can't we get a very good idea of both of...
  34. Y

    Practical measurements of rotation in the Kerr metric

    In another thread WannabeNewton mentioned: and gave this reference: Until WBN mentioned it, I had never given any thought to the difference between these methods of measuring rotation, so I would like to explore those ideas further here, particularly in relation to the Kerr metric. Consider...
  35. P

    Advanced Project - Wheatstone Bridge for TCR measurements

    Advanced Project -- Wheatstone Bridge for TCR measurements Ok, so I have to do this experiment on my own as part of my coursework this year and I picked something called the temperature coefficient of resistance. I think I basically have to determine the TCR or copper and I'm almost...
  36. D

    Find light bulb surface temp from temperature measurements

    Homework Statement I have 3 data points of steady state temperature at 3 locations some distance away from a bulb, I need to calculate the temperature of the surface of the bulb. It would be best to assume the bulb is a hemispherical radiation source, based on the experiment set-up...
  37. B

    Question regarding rotational measurements

    Hi, This isn't my field at all so please excuse my ignorance. Let's say I have a pipe positioned at 30 degrees to the horizontal and an inclinometer attached to the pipe in a vertical position. Now I rotate the pipe some amount about it's long axis. The inclinometer reads 15 (or...
  38. E

    Synchrotron X-ray Measurements

    I am curious about a question. in synchrotron station,people use x ray to do kinds of experiments. They use the x ray ,how do they know the characteristic(like wavelength,brightness) of the ray they use. Does they measure the x ray when they use it simultaneously? Does this have an bad effect on...
  39. 0

    How To Incorporate Sensor Uncertainties With Multiple Measurements?

    Lets say a sensor measures within accuracy of +/- 0.05N And you take multiple measurements and graph it out. (I.e., 5.12N, 5.15N, 5.05N...). What is the uncertainty of the final average? One way I read is: Sx = s/√N where s = std. dev. N = number of data points But...
  40. J

    Kalman Filter - Acceleration Measurements

    I am using a extended Kalman filter for the state estimation of a nonlinear system. The real system has accelerometers, so I need to include the acceleration of the system as part of my measurements with noise added (position and angular rates are other measurements). All of the Kalman...
  41. K

    Coupling constants, units and measurements

    I was thinking about units and started wondering about coupling constants. In unit-independent form, the fine-structure constant is defined as \alpha = \frac{k_e e^2}{\hbar c} I don't have a deep knowledge of particle physics but I know that there are weak and strong charges which enter the...
  42. Geofleur

    Reproducibility of measurements in quantum mechanics

    There is a statement in the Landau and Lifgarbagez volume on quantum mechanics that has had me puzzled for weeks now. They say (bottom of pg. 23): "If the electron was in the state psi_n [an eigenstate of f], then a measurement of the quantity f carred out on it leads with certainty to the...
  43. B

    Experimental measurements of relative magnetic permeability

    I am trying to measure the relative permeability of a few materials, but the numbers I'm getting don't quite make sense. Maybe someone here can figure out what might be going wrong. My setup is as follows. I'm making solenoids using 30 AWG magnet wire wrapped around ferrite, steel and wood...
  44. nomadreid

    Causation between states or only between measurements?

    In the use of the word "causation" can one say that one quantum state "causes" another if the two states are not measured? Or does the concept of causation only refer to a relationship between measurements?
  45. J

    Question About State Collapse and Energy Measurements in Infinite Well

    I am just starting out in self-study for quantum theory, so forgive me if my question seems elementary or completely misguided. In quantum mechanics, every wave function ψ can be decomposed into a linear combination of basis functions in the following manner: \Psi = \Sigma{c_{n}\Psi_{n}}...
  46. B

    How Does Quantum Entanglement Affect Electron Spin Measurements?

    This is a pretty basic question I believe. When you describe the state of a single particle, let's say its spin state, it can be in a superposition of different states (like up and down). When you do a measurement of its spin you'll either get up or down, since its spin state will collapse into...
  47. M

    Precise measurements in Quantum Mechanics

    It follows from the Expectation value postulate that an observable A, associated with the operator A^, can be precisely measured only if the wave function ψ of the system is an eigenfunction of A^ . Accordingly, the position and momentum of a particle can never be precisely measured because...
  48. M

    Error propagation question - when do we combine repeated measurements?

    Hi, say I measure something ten times and get x+d1x, x+dx2, ... where dx1, dx2.. are the measurement errors. Now, say I want to calculate something from these measurements according to: A = B(C(x)), Where A is what I want, and B and C are known functions. Which is statistically...
  49. Q

    Measurements in Quantum mechanics

    Ok so I'm currently revising my quantum theory course from this year and I've reached the section on the postulates for measurements in quantum mechanics. The one I'm having trouble with is "The only result of a precise measurement of some observable A is one of the eigenvalues of the...
  50. S

    Observables, Measurements and all that

    Hi Folks, I somehow cannot get the difference and have to admit that I am left confused. For a probability of measuring m with the operator M on state \Psi_i p(m|i) = <\Psi_i| M^{+}_m M_m |\Psi_i> = <\Psi_i| M_m |\Psi_i>. The average of an observable is defined as <O> = <\Psi_i| O...
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