# Tag Info

27

I don't know if it qualify as home experiment, but you can use the internet to get access to thousands of kilometres of optical fibres for free. It allows you to measure the speed of light in the fibres, which is c/n, where n is the refractive index of glass, i.e. 1.5. This corresponds to 2×10⁸ m·s⁻¹. Using ping, you measure a roundtrip time, that is it ...

21

Method The method is based on measuring variations in perceived revolution time of Io around Jupiter. Io is the innermost of the four Galilean moons of Jupiter and it takes around 42.5 hours to orbit Jupiter. The revolution time can be measured by calculating the time interval between the moments Io enters or leaves Jupiter's shadow. Depending on the ...

20

One common way of making these measurements is gravitational lensing. Basically, astronomers look at some distant object which is located directly behind the galaxy in question. Since the galaxy is so massive, it bends the light from the more distant object around it, so we see an image of the object displaced by some angle from where it actually is in the ...

20

There is a trick I have heard about before but never tried. The basic idea is to put a mars bar in a microwave oven for a short amount of time. First you remove the turntable, so the chocolate bar stays stationary. Then you turn the microwave on just long enough for the chocolate to start to melt. It should melt at the nodes of the standing field. You simply ...

16

Eureka! As Archimedes said, according to legend. In principle, "TheMachineCharmer's" answer is feasible, but I would recommend recording the change in the volume of water instead (if you need an accurate measurement), because (1) it could be difficult to measure the volume of the spilled water, and (2) it is also a little less accurate to do so. (Some water ...

16

Let me first list all of the possibilities I considered that I later rejected. This is far from exhaustive, and I'm looking forward to seeing other people's creativity. Bad Ideas Sit on a tire swing with the fan pointing to the side. Point the fan up, measure speed of rotation of the system on the tire swing. Get a laser or collimated flashlight. Point ...

14

It depends on your definition of "any memories". If you don't remember what a second is, there is no solution. If you remember the "old" definition (a day has 24 h on 60 minutes, each of it is 60 s), and live on Earth not to far from now, you can rebuild an approximate time standard. If you remember the modern definition, i.e. (the duration of ...

10

There are three relevant quantities involved here: the length of a meter, the duration of one second, and the speed of light. You only need to absolutely measure one of them, after which the other two can be defined in terms of the one that is measured. For technological reasons, we have chosen to make the measured reference quantity the length of one ...

10

The set of irrational numbers densely fills the number line. Even assuming that quantum mechanics doesn't disable the preimse of your question, the probability that you will randomly pick an irrational number out of a hat of all numbers is roughly $1 - \frac{1}{\infty} \approx 1$. So the question should be "is it possible to have an object with rational ...

10

Carbon-14 makes up about 1 part per trillion of the carbon atoms around us, and this proportion remains roughly constant due to continual production of carbon-14 from cosmic rays. The half life of carbon-14 is about 5,700 years, so if we measure the proportion of C-14 in a sample and discover it's half a part per trillion, i.e. half the original level, we ...

9

The Doppler shift in the light from the star tells you the period of the planet's orbit and also the velocity the star moves. You need to know the mass of the star, but this can be estimated to good accuracy from the star brightness and type. Once you know the mass of the star you can calculate the distance of the planet from it's period using: r^3 = ... 8 The best way of measuring the mass is in principle using gravitational lensing, as mentioned in the first posted answer to this question. However, applying this method has become feasible only relatively recently, partly because lensing is relatively rare and requires 'lucky' alignment of the source and the lens, and thus a large telescope survey to find ... 8 You could find a capacitor and read of its capacitance, alternately build one and measure it, and measure its dimensions. Now you can get a good estimate on the permitivity of vacuum, epsilon. There are possibly other intricate ways to measure this number. The speed of light is then given by a relation involving another number, the vacuum permeability, µ , ... 8 You might also want to try the rotating mirror method, of Léon Foucault. It is detailed here and here. The only difficult part is the rotating mirror, but it could probably be done with a drill. 8 It seems we have reached the point where simple models are no longer satisfying. Rather than posing ad hoc DEs maybe it's time to try an actual physical model. Short of doing a full hydrodynamic simulation (definitely overkill here) we can try what is called a lumped capacitance model where we divide the system up into a number of "lumps" and energy flows ... 7 I can't think of a way to do it with "common household tools" but if you have an oscilloscope, a laser diode, a couple of photo-sensors, a beam splitter, you can do it. All of these things are readily available from science supply/hobby stores online, but not usually in most homes. Set up the laser diode to hit the beam splitter and be split into two ... 7 According to what I understand you will show as weighing more on a carpet than on a hard floor. From what I understand it is due to the way the hard floor affects the feet of the scales. Here is a article that explores that question: http://www.newscientist.com/article/dn2462-people-weigh-less-on-a-hard-surface.html 7 For the state |x\rangle, if you repeat the same experiment with this initial state N times, you never get |1\rangle as the outcome. However, if you repeat the same experiment with |y\rangle as the initial state, the probability to get |1\rangle in each copy of the experiment is \epsilon^2. The results |1\rangle will appear infrequently, ... 7 The formula you've specified \Delta k = \sqrt{(\Delta k_1)^2 + (\Delta k_2)^2} $$is the formula to obtain error of quantity k, as being dependent on k_1 and k_2 according to the following expression$$ k = k_1 + k_2.$$Generally, to obtain experimental error of a dependent quantity (and the expression stated in your question), you start with ... 7 Alternatively I would look around the lab for an infrared thermometer. There exist in the market close focus ones that go down to 6mm in close focus option ( so as not to advertise, google space accurate infrared thermometers microscopes where I found the number in a one of the first hits). I would choose a large ant, or attract more by a spot of honey ... 6 To keep things simple, let's talk about two-qubit states. A single qubit could have an orthonormal basis \{|0\rangle, |1\rangle\}. But it could also have a different orthonormal basis \{|+\rangle,|-\rangle\}, where$$|+\rangle = \large(\normalsize|0\rangle \small+\normalsize |1\rangle\large)\normalsize / \sqrt{2}|-\rangle = ...

6

CODATA is a group that compares and combines all the most accurate experimental measurements of fundamental constants to give recommendations for best-guess values that should be used. They periodically update their values as new experiments are done. You are seeing that some wikipedia pages use old (not-updated) CODATA recommendations, while others have ...

6

The ultimate answer is the JCGM 100:2008 guide followed by most of the metrology institutes around the world. The specific chapter on combining uncertainties is Chapter 5. Specifically, for a two-variable function $f(t_1, t_2)$ of two random variables, Eq. (16) of Section 5.2.2. gives \Delta f^2= \left (\frac{\partial f}{\partial t_1} \right )^2 \Delta ...

6

These days planes measure their speed (and position) using GPS. In the old days (my father used to fly Tiger Moth's!) they would measure air speed for a rough guide, but correct their speed by spotting landmarks on the ground. In poor visibility it was not uncommon for pilots to get lost, sometimes resulting in tragedy when they flew into mountains or ...

6

It depends what you mean by "without an instrument". You need something to measure pressure with - your own senses won't be able to measure everyday pressure changes (though they could measure the change if for example you were thrown out of an airlock into space without a space suit). You can easily build a diy barometer. Just take a glass bottle turn it ...

5

If you believe wholeheartedly in Mach's principle, then there is no way to test empirically for rotation of the universe as a whole, since there is nothing else for it to be rotating relative to. However, general relativity is not very Machian, and it offers a variety of ways in which an observer inside a sealed laboratory can detect whether the lab is ...

5

Atoms have no sharp outer boundaries. All these things and clouds are probabilistic. The electrons always have a nonzero chance to be arbitrarily far from the nucleus, and so on. Moreover, the visual size of an atom will depend on the frequency of light one uses to "see" the atom, and so on. Assuming that you understand all these disclaimers and you only ...

5

The answer depends in part on what you mean by "measure". You can certainly calculate the acceleration using the laws of kinematics and dynamics, as Lawrence B. Crowell points out in his answer. Does that, in your mind, count as "measuring the acceleration"? Here's a much more direct recipe that I think would uncontroversially count as measuring the ...

5

The spin of a single electron has been measured since the very first moment when the people understood that every electron possesses a spin. A Stern-Gerlach experiment - a magnetic field - is enough to measure the spin: http://en.wikipedia.org/wiki/Stern-Gerlach_experiment

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