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Questions tagged [measurements]

For questions related to methods, analysis, accuracy, presentation, or interpretation of measurements. It is not intended for abstract quantum measurement questions such as how a wave function collapses during measurement or how the Heisenberg uncertainty principle constrains quantum measurements.

Measurement is the process of quantifying an attribute of an object, event, or system. Scientific measurements always consist of a definition of what is being measured, numerical values for the magnitude and uncertainty of the measured quantity, and the measurement unit.

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How do you make more precise instruments while only using less precise instruments?

I'm not sure where this question should go, but I think this site is as good as any. When humankind started out, all we had was sticks and stones. Today we have electron microscopes, gigapixel cameras and atomic clocks. These instruments are many…
Vilx-
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How do I experimentally measure the surface area of a rock?

I hope this is the right place to ask this question. Suppose I found a small irregular shaped rock, and I wish to find the surface area of the rock experimentally. Unlike for volume, where I can simply use Archimedes principle, I cannot think of a…
Pritt Balagopal
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How can you weigh your own head in an accurate way?

I read some methods but they're not accurate. They use the Archimedes principle and they assume uniform body density which of course is far from true. Others are silly like this one: Take a knife then remove your head. Place it on some scale Take…
user5402
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How do laser "tape measures" work?

There is a device available for about $\$40$, which fits in the palm of the hand, runs on two AA batteries, and can measure distances up to $50\,{\rm ft}$ to an accuracy of $\sim \frac{1}{8}''$ ($\sim 3\,{\rm mm}$). Light travels $300,000\,{\rm…
Anthony X
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Can photons be detected without being absorbed?

I am thinking about a detector that would beep if light passes through it. Is it possible?
Arik
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What if the universe is rotating as a whole?

Suppose in the milliseconds after the big bang the cosmic egg had aquired some large angular momentum. As it expanded, keeping the momentum constant (not external forces) the rate of rotation would have slowed down, but it would never reach…
John Alexiou
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Home experiments to derive the speed of light?

Are there any experiments I can do to derive the speed of light with only common household tools?
Justin L.
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What is the quantum mechanical definition of a measurement?

I hear the word "measurement" thrown around a lot in quantum mechanics, and I have yet to hear a scientific definition that makes sense. How do we define it?
mcchucklezz
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What is the most precise physical measurement ever performed?

Obviously some things, such as the speed of light in a vacuum, are defined to be a precise value. The kilogram was recently defined to have a specific value by fixing Plank's constant to $6.62607015\cdot 10^{−34}\frac{m^2 kg}{s}$. In particular, in…
Cort Ammon
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Why can interaction with a macroscopic apparatus, such as a Stern-Gerlach machine, sometimes not cause a measurement?

Consider a Stern-Gerlach machine that measures the $z$-component of the spin of an electron. Suppose our electron's initial state is an equal superposition of $$|\text{spin up}, \text{going right} \rangle, \quad |\text{spin down}, \text{going right}…
knzhou
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Why is a leading digit not counted as a significant figure if it is a 1?

Reading the book Schaum's Outline of Engineering Mechanics: Statics I came across something that makes no sense to me considering the subject of significant figures: I have searched and saw that practically the same thing is said in another book…
Vinicius ACP
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Why do we observe particles, not quantum fields?

My understanding is that, in the context of quantum field theory, particles arise as a computational tool. We perform an expansion in the path integral in some parameter, and the terms in these expansions correspond to Feynman diagrams which can be…
Charles Hudgins
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Easy to perform quantitative experiments at home

What are some easy to perform physics experiments that can be done at home (with not too much special equipment) and that allow to actually measure/plot data and draw conclusions from it? My son is pretty interested in everything physics and we've…
user1583209
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How is temperature defined, and measured?

In questions like this one, temperatures of millions of degrees (Celsius, Kelvin, it doesn't really matter at that point) are mentioned. But, what does it mean exactly? What is measured, and how? As I more or less expected, the Wikipedia article…
Martin Argerami
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Why are quantum effects of the apparatus ignored in quantum experiments?

When reading about various quantum experiments the apparatus often includes things like "semitransparent mirrors", "regular mirrors", "polarization filters" and others. Usually a photon or an electron is emitted, bounces around in the device, and is…
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