The result of sampling the property of a system

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22 views

Limits on the information obtained through optical measurements

Consider a Gedankenexperiment shown in the figure below. There are two lasers $S1$ and $S2$ with exactly the same specifications on paper. In practice, they are of course somewhat different but ...
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1answer
105 views

No length contraction!

Suppose a person standing on a platform were to observe and measure the length of a train passing by. Instead of the usual approach involving a clock and knowing the speed of the train, the person ...
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1answer
54 views

How can I measure a length of over 4 feet to an accuracy of 1/100th of an inch?

How can I measure a length of over 4 feet to an accuracy of 1/100th of an inch ? I want to make several metal standard bars of a particular lengths, some of which are over 4 feet and I want the ...
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2answers
90 views

Good way to compute the force of a hammer blow?

What is a good and easy way to compute and/or measure the force of a hammer blow, not using any fancy or specialized equipment? If the hammer is swung by hand through an arc, it is not obvious to me ...
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0answers
35 views

Easy to use particle tracking software [closed]

I'm a physics student and we have to do an experiment. We follow a microscopic sphere of diameter about 40$\mu m$ for 20 $sec$, in water. The sphere will travel a distance wich we have to measure in ...
3
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2answers
151 views

Decomposing light into frequency spectrum

Light hits a charge coupled element. The wavelength of the light somehow is translated into a color picture. Where can I learn about methods (algorithms) to decompose light hitting a CCD into ...
6
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5answers
720 views

Number of significant figures

I am looking for an intuitive answer that will explain me why there are only two significant figures in say the number 1500. Also definition from wikipedia: The significant figures of a number ...
3
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2answers
139 views

How to use an accelerometer to correctly quantify the magnitude of vibrations

Consider the following setup: An accelerometer is placed inside a helicopter, measuring $g$ values along three axes $(x,y,z)$ every $10~\text{ms}$ (100 times a second), during a helicopter flight. ...
3
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2answers
385 views

How to measure Entropy?

While $$\delta Q=T\ dS$$ allows for obtaining the entropy change of an isolated system in equilibrium by measuring the heat exchange with the environment, I was wondering whether there are ways to ...
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1answer
90 views

What is the difference between zero background radiation and field background radiation in Nuclear Physics measurements?

Can someone please explain the difference between these two terms (Zero Background Radiation and Field Background Radiation) used in radiometric prospecting measurements?
7
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1answer
273 views

Is it feasible to measure the energy of cosmic ray muons with a consumer Digital Single Lens Reflex camera?

I have read this article SIBBERNSEN, Kendra. Catching Cosmic Rays with a DSLR. Astronomy Education Review, 2010, 9: 010111. and it talks about estimating the muon cosmic ray flux by means of a DSLR ...
2
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4answers
53 views

Is there a maximum accuracy for positions in the universe?

I was thinking how, since an object in our universe can move from one position to another, it must have passed through all the positions between those two positions. (I am thinking it moved it a ...
9
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7answers
434 views

Can a ultracentrifuge be used to test general relativity?

With today's ultracentrifuge technology, they can spin so fast that the sample can be subjected to accelerations of up to 2 millions Gs. That is equivalent to two solar masses. Has someone tried to ...
0
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2answers
348 views

Is it possible to use induction ampermeter to measure power consumption of electric water heater and dryer?

I hope this practical question is not OT and not too trivial for this forum. I am renting an apartment in a duplex with a shared water heater and dryer. Turns out, both water heater and the dryer are ...
4
votes
2answers
46 views

How to measure temperature of a laser cooled sample at picoKelvin temperatures?

I'm reading about laser cooling.. my question is: how can the temperature of the sample be measured? (using laser cooling we can reach $10^{-12}K...)$
0
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0answers
33 views

What is source of Infrared Radiation from some solid object? [duplicate]

I use a Fluke infrared temperature measurement meter for various applications. I have not thought too much about the source of that infrared radiation until recently. Assume some solid with maybe a ...
0
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1answer
66 views

Question about the double slit experiment

If we measure a particle before it passes through the slit, would we see the particle or the interference pattern on the screen after the slits?
4
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3answers
362 views

Are negativity of the Wigner function and quantum behaviour equivalent?

I've read the following question: Negative probabilities in quantum physics and I'm not sure I understand all the details about my actual question. I think mine is more direct. It is known that the ...
0
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2answers
535 views

Measure mass difference of an object without a scale

For a project i need to separate items based on their mass in real time. I like to explore measuring weight of an object (round metal ball) by taking photographs (several) during free fall and ...
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1answer
48 views

Compatible Observables and Measurement

Suppose $A$ and $B$ are compatible observables (i.e. $[A,B] = 0$). We take the eigenkets of $A$ to be $|a_1 \rangle \ldots |a_N \rangle$. Further, we suppose that the first $k$ eignekets of $A$ are ...
3
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1answer
135 views

Is this the correct way to I combine multiple interdependant pressure readings?

I want to measure the density in different layers of a suspension. To do this I want to place pressure sensors at different heights. Let's assume that the sensors are not by orders of magnitude more ...
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3answers
56 views

How do we measure mass?

How do you measure mass? Weight is easy using a scale, but we can't measure mass that way, because then mass would be different on every planet. I know there was a Veritasium video (here) on defining ...
0
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0answers
23 views

Thermistor calibration - estimation of number of reference temperature points needed

A thermistor changes resistance with the temperature in a non-linear way and follows the exponential Arrhenius equation. Two reference points, ice slush water and boiling water, are used for ...
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0answers
22 views

Measurement of two qubits in a tensor product space

I understand that if we have two qubits, say $\Psi \in \mathcal{H}_1 \bigotimes \mathcal{H}_2$ where Alice has the first qubit, and she makes a measurement and ends up with the state $\phi \in ...
2
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1answer
127 views

Problem on Einstein - de Haas experiment

I am a Physics student (4th year) and I'm trying to study the Einstein - de Haas effect in laboratory. That is what I got: a suspended Iron cylinder with about 5 cm height and a radius of 0.8 cm is ...
2
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1answer
30 views

How to measure the fineness of a textile fibre by diameter and fibre length?

I measured the diameter (um) and the fibre length (cm) of different (loose) textile fibres and have an average. Now there must be a relation between these two factors that gives an idea of the ...
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0answers
56 views

measuring distances

We measure distances using half of the time of flight of light, 'a la Einstein'. What is the geometrical shape of the surface that is the locus of the points that are at a definite distance of an ...
1
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1answer
73 views

Do subatomic particles have dimensions?

We know atoms are mostly "made" out of empty space, so the nucleus and all the subatomic particle are very small in compared to the magnitude of the atoms. We also know that atoms are incredibly ...
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0answers
16 views

How does one measure the power factor?

How does one measure the power factor? $$\text{power factor}\equiv\frac{\text{power}}{|V||I|}=\frac{R}{\sqrt{R^2+(1/\omega^2C^2)}}$$ for an RC circuit driven with $V(t)=V_0\cos{(\omega t)}$.
11
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3answers
486 views

If time standard clocks and any memories about the time standard are destroyed, can we recover the time standard again?

Assume the time standard clocks and any memories about the time standard are destroyed. Can we recover the time standard again exactly? Recovering the time standard again means we can determine the ...
1
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5answers
125 views

The nature of measurement

Does the measurement of the particle change it's physical state? Or does it only seem to do that? Ex. if a particle was measured before the slits, would we see an interference pattern, or a particle ...
4
votes
2answers
644 views

Do the copper connectors we used in measuring the resistance of a wire contribute to the said measurement?

We measured the resistance of a wire by setting the multimeter to ohmmeter mode and connected the ends of the ohmmeter to the ends of the wire; and we also calculated the theoretical value using a ...
4
votes
2answers
125 views

Is there a naturally occuring sound pressure level reference?

There are lots of devices that purport to measure the absolute value of sound pressure levels. Here is an example, here's another, there's also this iPhone App. Putting such devices side-by-side in ...
21
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4answers
3k views

If the LHC-calculated mass of the Higgs is wrong, how long will it take to determine this with confidence? [closed]

After I watched "Particle Fever"--the movie about Large Hadron Collider (LHC) and the successful identification of the Higgs boson--I became a bit concerned with that team's handling of various ...
3
votes
4answers
141 views

How can I measure the speed of a figure skater's spin?

My daughter is a figure skater and needs to measure how fast she is spinning before she loses her position. This is a science project for 7th grade. I have looked for devices to possibly measure her ...
14
votes
2answers
5k views

Home experiments to measure the RPM of a pedestal fan without special equipment?

Is it possible to determine to an approximate degree, the revolutions per minute of a fan, for example a pedesal fan pictured below, without using some electronic/mechanical measuring device? One ...
6
votes
1answer
317 views

How do bathroom scales measure body fat percent?

My bathroom scale has 2 metal strips each for a foot and the producer claims that it can measure body fat percent. There is a warning in the manual, that if I have heart problems (I guess pacemaker), ...
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0answers
32 views

What technologies are available to measure distance? [closed]

I'm a programmer, I really lack of physics knowledge, I'm trying to make some basic design for a distance measuring simple system, for a social project I'd take as hobby. Basically I would have many ...
1
vote
3answers
112 views

Does every interaction of quantum objects introduce backaction?

The motivation of this question is the following experiment: Assume you have quantum mechanical oscillator, e.g. a particle in a potential $V(q_x)\propto q_x^2$. Now the position of the particle ...
0
votes
1answer
61 views

Distinguishing between prepared and unprepared states Stern-Gerlach experiment

$ \newcommand{\bra}[1]{\left\langle #1 \right|} \newcommand{\ket}[1]{\left| #1 \right\rangle} \newcommand{\braket}[2]{\left\langle #1 \middle| #2 \right\rangle}$I have a problem and am confused as to ...
2
votes
0answers
80 views

Molecular structure correction factor in Mass Flow Controller

This question concerns device called Mass Flow Controller (or Mass Flow Meter). For a video explaining the principle: see https://www.youtube.com/watch?v=G62ma2IFh9o These devices are factory ...
1
vote
0answers
51 views

Justifying the use of real numbers for measuring length

I am not sure if this is the most appropriate place to post this but here goes nothing: Assume we were trying to come up with system of numbers $S$ to model our intuition of length. We want $S$ to ...
0
votes
1answer
47 views

Light speed measured by observing Jupiter moons [duplicate]

The famous discovery that the light has speed measures the times of the immersion and emergence of Io, one of Jupiter's moons. However, I still can't comprehend this. Even when the Earth is further ...
19
votes
1answer
2k views

How did Rømer measure the speed of light by observing Jupiter's moons, centuries ago?

I am interested in the practical method and I like to discover if it is cheap enough to be done as an experiment in a high school.
0
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1answer
42 views

How much time between measurements do you have in order to make the same measurement on a particle?

As I understand it, you can make a measurement on a particle and if you quickly carry out a second measurement you will get the same outcome as the prior measurement. If this is the case, how much ...
4
votes
10answers
2k views

Is it possible for a physical object to have a irrational length?

Suppose I have a caliper that is infinitely precise. Also suppose that this caliper returns not a number, but rather whether the precise length is rational or irrational. If I were to use this ...
7
votes
5answers
941 views

Proving and demonstrating vacuum in container without breaking it

Let there be a hollow container made of glass or some other transparent material, roughly the size and shape of an apple. Let the walls be of sufficient thickness for the container to be safely ...
0
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2answers
66 views

How to calculate the error in measurments of derived quantities knowing the error in basic quantities?

I wonder how to calculate error of a derived quantity $z$ knowing the error of all quantities that $z$ depends on say $x$ and $y$. For example: Suppose I want to calculate the speed of a body ...
4
votes
2answers
72 views

Examples of (classical) measurements that are not independent?

What are some simple examples of measurements that are not statistically independent, i.e. with nonzero covariance? I'm looking for real examples that might reasonably come up in an undergraduate ...
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1answer
129 views

Thought Experiment: Force on magnets in a Stern Gerlach Experiment

Background: In the SG experiment, an inhomogenous magnetic field affects a force on particles passing between two magnets. "Measurement" takes place when a screen is placed on one end, blocking one ...