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1500 questions
35
votes
8 answers
Is it possible to "pump" a powder?
Is it possible to "pump" a powder the same way liquids can be pumped?
If so, what are the challenges? If not, what are some alternatives?
peterh
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33
votes
3 answers
Why are two wires used in railway overhead equipment?
While watching the train videos, I came across these overhead wires. After searching on the internet, I found that both catenary and contact wires carry the same voltage and are connected by vertical wires called "droppers" at intermediate points…
mech_duck
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32
votes
4 answers
Why dig out and then fill in before building a large structure?
I work in the middle of London, in an area full of large office blocks. Across the road from my office they have started construction of a large building (10 stories plus). Over the last few weeks, diggers have dug a large (and vertical walled)…
AndrewD
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31
votes
4 answers
What is the lowest point below sealevel that we have built where a human can go?
According to google searches, the Jinping Underground Laboratories are the "deepest" building or buildings constructed, reaching 7900 feet (2400 metre) below the surface.... However, the surface in question is a mountain. While that does classify as…
Chris Gergler
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29
votes
4 answers
How can a piece of paper be shaped to guarantee it falls slower than a plain sheet of paper?
My son and I are playing "MAKE" (think "HORSE") and we challenged ourselves to build the slowest falling object using only a sheet of paper. We cannot build anything that falls slower than a plain sheet of paper. Any ideas?
Corey Alix
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29
votes
4 answers
Which is Worse: Car vs. Car or Car vs. Wall?
So I got myself questioning what could be worse for the driver... a collision of two identical cars at equal speed (frontal crash) or the same car with the same speed crashing through a wall? The first case I see it would double the impact, but also…
Alessandro Nardinelli
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29
votes
11 answers
Is it possible to build an air compressor with no moving parts?
Is it physically possible to build an air compressor with no moving parts? I'm envisioning a thermodynamic cycle capable of compressing air with no moving parts and operated in a stationary way. There is no limitation on the compression factor,…
user3368561
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29
votes
4 answers
Why do hydraulic systems use special fluid - what's wrong with water?
As a hydraulics layman thinking about hydraulic systems, it seems that the important factor is to have a liquid that doesn't compress much or at all. Doesn't water meet this requirement, and what other properties should the liquid have (if any) that…
jhabbott
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29
votes
10 answers
How to quantify martial arts strikes?
Subtitled: Ah, strong am I with the Force, but how do I measure it?
With all due apologies for paraphrasing Yoda, I am trying to measure a force. Fortunately, it's an easier force to measure than midi-chlorians.
When I tutor others in karate, one…
user16
28
votes
4 answers
How are increasingly accurate machines made?
Making extremely accurate machines seems like a chicken and egg problem. How do you make one if you don't already have one?
For example, how was the first indexing head made without an indexing head to make the indexing plate? How was the first…
Kevin Krumwiede
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27
votes
5 answers
Why are engine blocks so robust apart from containing high pressure?
Lately, I've been pondering why some engine blocks are so bulky, I always thought intuitively it was because they had to last a long time whilst containing thousands of combustion cycles but the more, I look into the reality of engine design that…
David Nolan
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27
votes
3 answers
Calculating pitch, yaw, and roll from mag, acc, and gyro data
I have an Arduino board with a 9 degree of freedom sensor, from which I must determine the pitch, yaw, and roll of the board.
Here is an example of one set of data from the 9-DOF sensor:
Accelerometer (m/s)
$\text{Acc}_{X}$ = -5,85
$\text{Acc}_{Y}$…
MaltDew
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27
votes
1 answer
Understanding required torque for a motor lifting a weight
This is a continuation of me trying to understand torque and stepper motors in my other question. I'm trying to understand the torque a motor would be required to generate to lift a small weight, and the formulas involved.
The first part of my…
confused
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27
votes
9 answers
Why use steam instead of just hot air?
As I understand, a steam machine needs a pressurised gas to work. This can be compressed air but it used to be steam. Energy was provided to the steam engine by heating up water. I don't understand why it used water as the pressurised gas could have…
Manu H
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26
votes
6 answers
What did all those valves do in a U-Boat?
I was visiting the Museum of Science and Industry in Chicago (highly recommended) and I took the tour of the complete U-Boat (U-505) that they have housed there. It's extremely well-preserved inside and quite fascinating. However, the guide was not…
Tim Smith
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