44 votes

How can I measure correctly with a ruler?

For this answer, I'll be using this terrible excuse of a ruler, where is the lines indicating each millimeter and the . is ...
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  • 13k
28 votes

Is it possible for a bicycle chainwheel to have a fractional number of teeth?

Gear ratio This is a Roller Chain drive system, and as such it's a timed system. The ratio between the two connected pieces depends entirely on the number of teeth on either end. Even if you ...
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  • 1,106
28 votes

How can I measure correctly with a ruler?

You should include the thickness of one total line. In an ideal world, one would measure the the centre of each line (marked 'also correct' below). In this case, you're including half of each line. It'...
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21 votes
Accepted

What unit of weight is that?

You are probably right (it being of Russian origin). The weight seems to be 5 funt. 1 funt is the Russian equivalent of a pound. It is written as Фунт, funt, and around 1900 it was the basic unit of ...
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  • 22.6k
18 votes
Accepted

Is it possible for a bicycle chainwheel to have a fractional number of teeth?

I suspect that the answer to this is that, ultimately the gear ratio comes from the ratio of diameters of the gears rather than the number of teeth, although in most circumstances practicality ...
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14 votes

How to quantify martial arts strikes?

You could just hit a pendulum and measure the angle to which it swings. I have found that three liter soda bottles filled with water and hanging from a rope are good for hitting. Knowing the weight of ...
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  • 141
14 votes

How is gas flow through (extremely long) pipelines monitored and controlled?

It's important to remember that these pipelines don't exist as a single isolated line and will have a number of branches that tie into the main pipeline and split off for gas to be sold to different ...
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13 votes
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Can I use a ultrasound sensor to measure water level?

Technology used in depth finder, in marine application is mostly like is the best to measure the water from the top. To measure water level from the bottom of tank one could use a piezo electric ...
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13 votes
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What are grads used for on a scientific calculator?

Grads were developed by the French as part of the metric system and have been referred to as the metric degree. In some countries in Europe surveyors use grads instead of degrees. The other use is by ...
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  • 9,447
12 votes

Practical setup to measure angular velocity

Probably the easiest practical method to measure the frequency of a spinning top with everyday equipment is to analyze the sound created by the motion and look for the characteristic frequency. This ...
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  • 221
10 votes

How to quantify martial arts strikes?

I think what you want is a piezoelectric pressure sensor. You might be able to steal one from an old bathroom scale, but the sensors in a scale may only be good up to ~100 lbs of force. These ...
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10 votes

How to quantify martial arts strikes?

I think that an impact force sensor is what you're looking for. I'm not sure how expensive the linked sensors are so you could also use an acceleration sensor and do a little math. The second option ...
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10 votes

Can redundancy be used instead of periodic calibration?

There are a few basic issues. The premise of this idea is that the errors of each measurement device will balance out, so with enough devices, the average value will stay roughly accurate. If not, at ...
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  • 4,501
9 votes

What was that?! Quantifying the impact of a martial arts strike

The basic problem is that you haven't defined what a "good" kick or punch is. Is the purpose make the opponent lose his balance? To inflict the maximum pain? To break bones? To hit a particular ...
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  • 11.2k
9 votes
Accepted

What is the "tl" unit of weight measurement?

It could be a tola. 1 tola = 3/8 troy ounce (exactly) = 11.66g (approx.), so 10g = 0.857 tolas. If the scale has an accuracy of 0.01g (it's not very clear from the ebay description!) that would be ...
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  • 12.5k
8 votes
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How to know whether the flow is supersonic in a nozzle?

From my brief involvement in shocks, I think the most likely solution would be to image the exhaust, probably optically, but maybe using interferometry or something depending on what the exhaust is. ...
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  • 1,025
8 votes
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What instrument does a surveyor use to accurately find North?

Gyrotheodolites are an older, but accurate way to find true north. They can be used on the Earth's surface, but these days they tend to be used for surveying underground, in tunneling and mining ...
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  • 9,447
8 votes

Is it possible for a bicycle chainwheel to have a fractional number of teeth?

A "44.2 tooth" gear still can only push 44 links of chain per revolution, which pushes a 16 tooth cog around 2.75 times. There's no getting around that. I think that is the question that has everyone'...
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7 votes
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How does a multimeter protect itself from high voltages?

WARNING: Note that some cheap meters are not suitable for use with 230 VAC AC mains. Some meters may have AC voltage ranges able to conceptually measure to well above AC mains voltage BUT have ...
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7 votes

How does a multimeter protect itself from high voltages?

Simple answer is good multimeters have good protection circuts. When the measuring source outside of the meters capabilities of the meter, the meter will give out of range message. There are four ...
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7 votes
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Practical setup to measure angular velocity

There are several ways. The most direct is to paint half of the top white and the other black, then point something with a light sensor at it. AC amplify the output a little, then determine the ...
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  • 11.2k
7 votes
Accepted

How much current is this phone drawing?

This answer is based on extra information provided by the OP in the form of a photo. The claimed currents were far too low due to a misunderstanding in how to read the meter's 10A range display. The ...
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7 votes

What are grads used for on a scientific calculator?

Gradians are commonly used in land surveying. I only know this because I made the mistake of asking the same question of a Civil Engineer.
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  • 2,135
7 votes

Seeing through walls and noninvasive structural integrity metrics

Depending on the region and structure of building the techniques might vary. Below are few suggestions Termite inspection is another popular method to determine the structure integrity of building. ...
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7 votes
Accepted

Units to use in this formula?

You can use any consistent set of units. That includes SI. But if you try to use a pressure in ATM, a sphere radius in feet, a wall thickness in mils, and want the stress in tons per square inch, you ...
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  • 12.5k
6 votes

How to quantify martial arts strikes?

Conductive foam will change it resistance when compressed, so it makes a good, cheap force sensor, as long as you have a system to make many measurements in quick succession and remember the one with ...
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6 votes

How does measurement uncertainty combine with tolerances?

There are two different aspects in your measurement. On the one hand, you are dealing with tolerances. On the other hand, you cover probabilities in measurement systems. Just for a rough calculation: ...
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  • 215
6 votes
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Measuring longer distances with high accuracy

To get that sort of accuracy over that scale is not trivial and probably won't be cheap. For smaller size up to a few meters a portable CMM would be an option (here's an example). These have accuracy ...
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  • 1,025

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