The result of sampling the property of a system

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970 views

Uncertainty in Acceleration given the uncertainty in position

I had a motion detector record the position of a dynamics cart and automatically plot Position vs Time and Velocity vs Time plots in Logger Pro on the computer. If the instrument uncertainty in ...
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1answer
124 views

Experimental perspective in understanding the Heisenberg Uncertainty Principle

I need to confirm whether or not I understand Heisenberg Uncertainty Principle. So the crucial thing is that you need an "ensemble" of measurements: $$\delta x \delta p \ge \frac{\hbar}{2}.$$ If I ...
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1answer
2k views

Why is carbon dating limit only 40,000 years?

For an example, when they tried to get the carbon dating for presence of Aboriginal people in Australia they get to the number 40,000. But it could be much earlier. Why is that 40,000 years limit for ...
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0answers
36 views

where to find sample fluid stirring data?

I want to find some force data for fluid stirring. Originally I intended to record the data using my force sensor, but it doesn't have the resolution to read stirring force for Newtonian fluid. ...
3
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2answers
128 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 ...
2
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1answer
105 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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1answer
557 views

What's the difference between 'least count' and 'smallest division'?

I'm wondering the difference between the 'least count' and the 'smallest division' of an instrument. Can you explain that for me, plz?
7
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1answer
835 views

How to measure a solid-solid surface energy?

Many techniques exist to measure the surface energy between a liquid and a liquid or a liquid and a gas (see e.g. the wiki page). Methods to measure the surface energy between a solid and a fluid are ...
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1answer
247 views

Practical method to weigh human limbs with common household items?

What methods could be used to determine (or estimate within a reasonable margin of error) the mass of a living human's limbs, short of cutting them off? And more interestingly, how can this be done ...
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1answer
328 views

Quantum computing problem [closed]

Suppose that a qubit is in the state $|\varphi\rangle=a|0\rangle+\sqrt{1-a^2}|1\rangle$, where $a\in[-1,1]$. If we first perform a standard basis measurement on this qubit and then perform a ...
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1answer
173 views

Measuring acceleration of a bus using water between two sheets of glass

I was riding a bus one day and noticed that the double windows had some water between them. As the bus accelerated, the water collected to the sides, first forming a trapezoid and then a right ...
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1answer
92 views

Multimeter has a resistance

If a multimeter has a resistance (1M ohm, say) when measuring voltages how do I take that into account in my error?
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1answer
513 views

Does photon have size measurement because of its particle nature

Does photon have size measurement because of its particle nature like electron's 3.86*10^-13m etc..
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3answers
243 views

Setting up a local-coordinate system in space-time using only a single clock and light beams

I have a question to ask about the operationalist view of space-time. I am a mathematician who happens to be interested in physics, so if anyone thinks that my question is a silly or vague one, please ...
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1answer
354 views

Photometer: measured Irradiance L converted to photon rate

I am conducting an experiment in which the power meter reading of $410\,nm$ narrow bandpass stimulus is noted to be 30 $\frac{\mu W}{cm^2}$ at a distance of 1 inch away from the light source. I wish ...
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10answers
990 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 ...
3
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1answer
595 views

Finding radius of Earth through observation of Sun's motion

The question I'm about to pose is from a physics book I had recently bought. Since I am very interested in physics I am quite keen in understanding how this question can be solved. Before I present ...
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0answers
64 views

Experimental data for gas flow through pipelines

Maybe some of you could point a good source of experimental data of gas flow through pipelines? What I need is a very simple flow of some gases through some diameter simple linear pipeline. A graph of ...
2
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0answers
1k views

How to calculate uncertainties of a natural exponential function?

(I apologize if this should be posted in mathematics, however I chose to post it here as it's technically about physics) I conducted an experiment in which position of items were shifted on an ...
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1answer
97 views

Measuring the quantum state of light

A clarification please The following scheme to measure linear polarization states (a single polarizing beam splitter and two photo counters) orientation (as $arctan \sqrt{\frac{v}{h}}$) of coherent ...
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0answers
108 views

Measurement in Quantum mechanics

I have got a quantum conservative system whose Hamiltonian is $H$. I consider an selfandjoint operator $O$ whose eigenvalues and eigenvectors are: $$O|\psi _{n}\rangle = \lambda _{n}|\psi ...
3
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1answer
70 views

What methods exist for us to measure the position and momentum of atoms that make up molecules?

In this paper, Localization of an atom by homodyne measurement. A. M. Herkommer et al. Quantum Semiclass. Opt. 8 no. 1, p. 189 (1996) (paywalled). the authors are able to localize atoms using ...
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1answer
62 views

When are leap seconds added in various time zones?

I understand that technically when a leap second is added, it is added after midnight UTC, but I'm unclear how the addition is handled in other timezones. For precise reckoning of course (e.g. ...
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3answers
302 views

experimental technique for measuring temperature of an ant

I am taking a course on thermodynamics. I have a question from my text(halliday & resnick,physics-1). They asked me to measure temperature of an ant or an insect or a small body,like a small ...
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1answer
116 views

Basic question about probability and measurements

Say I have a Galton box, i.e. a ball dropping on a row of solid bodies. Now I want to calculate the probability distribution of the movement of the ball based on the properties of the body (case A). ...
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1answer
170 views

What will happen when measuring unmeasurable object?

There is a set called Vitali Set which is not Lebesgue measurable. Analogously, there also exists a Vitali set $Y$ in $\mathbb R^3$ which is a subset of $[0,1]^3$ and $|Y\cap q|=1$ for all $q\in ...
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3answers
5k views

Rough, easy DIY method of measuring magnetic field strength

How to easily, using standard DIY equipment measure the strength of magnetic field generated by a permanent magnet? Narrowing down the "loose language" of the above: strength of magnetic field: ...
5
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2answers
367 views

Averaging decibels

Wikipedia: The decibel (dB) is a logarithmic unit that indicates the ratio of a physical quantity (usually power or intensity) relative to a specified or implied reference level. If I ...
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2answers
153 views

Mean of a measurement on periodic data: what is the use of the inverse of correlation length?

Correlation and autocorrelation is something that in my Bachelor's programme in physics has been somewhat overlooked, so I'm in trouble understanding their use in this paper (The prisoner’s dilemma on ...
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1answer
64 views

Uncertainty writing

This will sound like a silly question, but I don't recall that my professors ever though me what this means. For example: X=1.2345(6) units This is uncertainty, that much I do know, but does it ...
3
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1answer
104 views

If the observable universe keeps expanding would we eventualy see light 24/7… clouds permiting? [duplicate]

If we can see more observable universe could there be a time when day and night looked the same?
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1answer
57 views

How to compare differences in waves?

I have a series of waves that I would like to compare to one another. The measurements are two-dimensional with time on the x-axis and an intensity measurement on the y-axis. I'd like some way of ...
7
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1answer
371 views

Weinberg angle measurement methods

I was reading up on the history of $W/Z$ bosons today and I got a little puzzled. I always assumed that people measured $M_Z$ and $M_W$ and then derived the Weinberg angle. But it appears that they ...
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1answer
905 views

Why does an infrared thermometer display very low temperature when being directed to the outer air?

I'm toying with an infrared thermometer - one which you point onto an object, press the button and it instantly measures the temperature by estimating the infrared radiation from the object. It shows ...
4
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4answers
325 views

Does entropy decrease through measurement?

For an electron in its rest frame, we have an entropy $$ S = \log 2, $$ which comes from the 2 possible spin directions along z-axis. If the measurement $S_z$ changes its state to $\left| + ...
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1answer
254 views

Controlling the outcome of a quantum measurement through translational entanglement

According to the paper: A. S. Parkins and H. J. Kimble, Phys. Rev. A 61, 52104 (2000). http://pra.aps.org/abstract/PRA/v61/i5/e052104 You can entangle position and momenta of two atoms by using ...
2
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4answers
384 views

Does measuring destroy entanglement

Before measuring a quantum particle(photon) it exists in a superposition state, once we observe(measure) it, it settles in one of the possible states(destroying superposition). For entangled ...
2
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0answers
211 views

How do I do error calculus right using gnuplot as an example?

Given is a set of measurements with their respective errors for example an energy spectrum. In gnuplot one is to fit a function $ f(x;\{p_i\})$ depending on a variable $x$ and on fit parameters $p_i$. ...
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1answer
1k views

How do astronomers measure the distance of the planets from its star?

I know they have accurate means of measuring the distance of the planets in the Solar System from the Sun. I'm skeptical how can they use the same tools or techniques for other systems so far away as ...
3
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2answers
434 views

Atomic clocks and how to synchronize them

During teaching measurement section in the class, Our teacher told us about atomic clocks. I have two questions: What is exactly an atomic clock? and how do we synchronize two atomic clocks far ...
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2answers
383 views

How to correctly solve density tolerance

I want to know if my solution to a textbook problem has any major problems with it. Here is the problem: Ethanol has a given density of 0.789 g/mL at 20 degrees Celsius and isopropanol has a given ...
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2answers
151 views

What is the fundamental reason for noise?

I have read that noise is a result of there being "no such thing as a perfect one-way valve". That energy transfer is never perfectly one-way; there will always (at some level) a finite flow of energy ...
5
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1answer
237 views

How do I measure the temperature of a tiny water droplet?

How do I accurately (+/- 0.1 degrees Celsius or better) measure the temperature of a small (5 to 50 microliter) water droplet without noticeably affecting its temperature? The mass of a thermistor or ...
1
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0answers
62 views

Efficiently distinguishing mixed quantum states?

Assume we know two different mixed states, p and q, and an efficient (quantum) algorithm for creating such two. Does it follow that there exists a computationally efficient method/measurement for ...
1
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1answer
169 views

How precisely can we date the recombination?

The early universe was hot and opaque. Once it cooled enough, protons and electrons were able to form hydrogen atoms. This made the universe transparent, and was known as recombination. We can see the ...
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2answers
208 views

Very basic question on spin

Can anyone give a simple explanation for what the fractions and integers mean in particle physics when describing spin? I've seen on another forum (the naked scientist) that it should not be thought ...
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2answers
516 views

Magnitude refers to number or number with units?

This question is about terminology for physical quantities. When we talk about magnitude (while talking about scalars and vectors) do we refer to just number or Number along with units? example: If ...
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1answer
327 views

Quantum Zeno effect and unstable particles

Is it possible to increase indefinitely the lifetime of unstable particles by applying the quantum Zeno effect? Is there a bound from theoretical principles about the maximum extension one can get in ...
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3answers
315 views

Significant Figures [closed]

Subtract 0.2 J from 7.26 J. Express your answer to the correct number of significant figures for the given data. I think its 7, but the answer is 7.1. HOW?
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1answer
144 views

Is there a way to measure atmosperic pressure without an instrument?

Just that . I am not too much concerned about the accuracy of measurements .