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1500 questions
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6 answers
How to make smoke for a small wind tunnel?
I am making a small (desktop) wind tunnel for educational purposes, I want to have 10 fairly thick smoke-streams about 3cm apart. I have experimented with incense but the stream is not thick enough and barely visible.
I was thinking of using a pipe…
jhabbott
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Is it structurally sound to cut an I beam to a T on one end?
I'd like to confirm whether the replaced beam in the attached picture is structurally sound given the end was cut to a T instead of an I. I had a qualified structural engineer approve the work but I'm curious about the engineering properties of the…
markroth8
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What are the engineering principles for a train to get electricity from the railway
How many general methods are there for transferring electricity from the railway to a train? I could see that some trains are connected by a pantograph and some have a third rail.
Are there any other methods? What is the general engineering…
havakok
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Pound-force (lbf) vs Pound-mass (lbm)
Given:
My thermodynamics text reads as follows:
In SI units, the force unit is the newton ($N$), and it is defined as the force required to accelerate a mass of $1\cdot kg$ at a rate of $1\cdot\frac{m}{s^2}$. In the English system, the force unit is…
Jules Manson
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2 answers
Why are earthfills fully covered in concrete where they join bridges?
Here's how a typical earthfill carrying a roadway joins a typical bridge
Parts of the earthfill slopes are greenish - that's grass - and parts are whitish - that's concrete.
The earthfill slope is fully covered in concrete where it joins the bridge…
sharptooth
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1 answer
Sizing a pressure safety valve for two-phase flow
I understand that valves in two-phase vapour / liquid were sometimes sized by considering the required vapour and liquid flow rates separately, and then adding the results together. But this is now considered an outdated practice.
I have also heard…
SecondVector
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6 answers
Why did steam locomotives not transfer power by cogwheels?
Modern cars use cogwheel to transfer power from the engine to the wheels.
Steam locomotives used some kind of bars (sorry, I'm not a native speaker) to transfer the power to the wheels.
Why did the engineers not use cogwheels?
Would steam…
J. Doe
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3 answers
Does a roadway bridge experience more load when vehicles are parked or when they are moving?
Bridges are designed for the loads that come from the vehicles that are expected to cross them. This includes the weight the vehicle and any dynamic loads that may be introduced from movement of the vehicle. Dynamic loads may be from "bouncing" or…
hazzey
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3 answers
Windmills in empty fields. Why no trees?
I have noticed that windmills are generally built in empty fields with no trees around, and I've been wondering why...
A windmill is generally way taller than trees and I can imagine that trees don't actually affect the flow (see picture).
But is…
Physther
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4 answers
What are the major differences between Engineering degrees and Engineering Technology degrees in terms of employability?
What difference in education occurs between two graduates, one with an Engineering Technology degree (be it Civil, Mechanical, Electrical...) and the other with the equivalent Engineering degree "proper?"
Assuming both degrees are 4 year degrees and…
cKrug
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3 answers
How does a traffic light sense the proximity of vehicles?
Some traffic lights don't operate periodically but instead detect when a car is close by and then turns green. I have heard that they use a magnetic sensor embedded in the road to sense cars as they come near. Is this correct? Do they use other…
FullmetalEngineer
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3 answers
What is the purpose of building foundations?
According to many sources, one of the purposes of building's foundations is "To distribute the weight of the structure over large area so as to avoid over-loading of the soil beneath." (Wikipedia)
On the Wikipedia page on foundations, there is the…
S. Rotos
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19
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7 answers
Effective ways to drive a single shaft with multiple motors?
To head off the "why not use a bigger motor" question, I'm a high school mentor for an FTC (First Tech Challenge) robotics team, with a bit of a soft mechanical / hardware background. They're somewhat limited in what they're allowed to use, motors…
trycatch
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1 answer
How many train passes can railway tracks endure?
I know that the rubber on car and truck tires wear, and the road concrete wears out. I wondered:
While steel is hard and elastic, it still causes friction (interaction
between molecules) and therefore abrasion.
Let's say we have on average 20-30…
Thorsten S.
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2 answers
Why are truss bridges the way they are?
Just by taking a train ride across my home city I can see truss bridges like the one in above picture everywhere. There are numerous variations, but the most common design seems to be this. But why are they built specifically this way?
I can…
S. Rotos
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