Tag Info

Hot answers tagged

93

Get someone to relax their neck as much as possible, stabilize their torso, then punch them in the head with a calibrated fist and measure the initial acceleration. Apply $\vec F=m \vec a$.


37

Thanks a lot for your votes for the "answer" below. Unfortunately I think now the solution does not work. It is great for two slices, but that is the end. There is another solution that should give 3 slices, which is still a bit short. And I am afraid I do not see how to use the two available steps to start building a recursion :-) Why ? It is clearly ...


37

Petroleum engineers would all provide you with the same answer "use Compton scattering", as this is how the mass density of rock formations gets measured deep in oil wells. A more complete answer is: Compton scattering can provide you with a measurement of the bulk density of your head. Combine this with a volumetric measurement (dipping your head in a ...


36

Step 1: Take a trip to deep space (space suit recommended; means of transportation left as an exercise for the reader). It is important to compute the Hill sphere of your body to make sure it is large enough at this stage. Really it's a Hill-roughly-person-shaped-spheroid-blob, but feel free to assume a spherical you to simplify the calculation. Step 2: ...


33

Here are some methods I came up with: Newton's Method: Measure the whole body's mass, let's call it $M$ Now detach the head, and put it a distance $d$ apart from the body Measure the gravitational attraction of the two parts of the body(let's call it F) We have a system of equations to solve: $$m_1+m_2=M \\ \frac{G m_1 m_2}{d^2}=F \\ \Rightarrow ...


32

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 ...


26

I would do it like this: The muscles of the neck have to be as relaxed as possible so that it approximates a flexible linkage, such that at some point along this linkage (which we can identify as the division between the head and the body, and thus the mass of the head includes a portion of the neck), if we separate the body into two free-body diagrams, ...


24

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 ...


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 ...


21

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 ...


19

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 ...


19

The uncertainty principle should be understood as follows: The position and momentum of a particle are not well-defined at the same time. Quantum mechanically, this is expressed through the fact that the position and momentum operators don't commute: $[x,p]=i\hbar$. The most intuitive explanation, for me, is to think about it in terms of wave-particle ...


17

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 ...


17

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

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 ...


16

1 Person A lays down on a carousel with its neck over the edge. Person B knocks A out. Person C spins the carousel. B clocks the time. Person D takes pictures of A's head as it goes around. 2 Measure the angle of the head by looking at the pictures. 3 Do the vector math.


15

You send the box and liquid towards a barrier equipped with a gauge to measure force. The setup looks like: When the box hits the barrier it stops, but the liquid inside it keeps moving. A short time later the liquid hits the side of the box and it too stops moving. So when you record the force at the barrier as a function of time you will get two peaks, ...


13

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 ...


11

Assume the body to be made of N sections $S_i$ of uniform linear density $\lambda_i$ and length $l_i$ and center of mass $r_i$ (from one end). Increase N as much as you want to get a more accurate reading. The sections need not be of the same length. Try to slice your body into approximately homogenous sections (homogenous with respect to mass-per unit ...


11

I took @AlanSE's advice and downloaded Audacity and did a number of measurements. There are some challenges - what is the snap in the snap? Does it start with the sound of your finger gliding over your thumb, and where does it end? I recorded my snap under definite sub-optimal conditions, using the built in microphone of an iMac inside a 14x10 office with ...


10

With a clock and a telescope you could repeat Rømer's determination of the speed of light.


10

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 , ...


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

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 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 ...


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 = ...


9

If you have a smart phone with a flash, you probably have a strobe feature at your disposal. You can put a drinking straw into it and record the sound it makes, and measure the frequency in sound-editing software. Imagine the fun explaining this to paramedics. Similarly, a laser-pointer, a mirror, and a photo-diode cleverly hooked up to your computer's ...


8

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 ...



Only top voted, non community-wiki answers of a minimum length are eligible