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1500 questions
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1 answer

Why does the Channel Tunnel enter the ground around 10 km from the coast?

I know that digging tunnels is always much more costly than building ways or train above ground. Why doesn't the Channel Tunnel start around the coastline? Why does it have an around 10 km long portion under land on the British side?
peterh
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How much can Protactinium degrade the efficiency of the Thorium fuel cycle?

One of the counterpoints to the Thorium fuel cycle is that Protactinium, which is generated in this cycle degrades reactor efficiency and thus needs to be removed, at least from the liquid fluoride or molten salt reactors. However, as far as I can…
Fizz
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What makes suspension bridges unsuitable for railways?

I recall reading in an old issue of Model Railroader an article about railroad bridges. In it, the author mentioned that you shouldn't have a model suspension bridge for a railroad track on your layout because no such arrangement would be…
Dave Coffman
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Would it make sense to have a 12V lighting circuit in a house?

Modern LED bulbs must convert the standard household supply (for example $240\text{V AC}$ in the UK) into a DC supply at a lower voltage (usually $12\text{V DC}$ I think) for the LED array. This is done on a per-bulb basis. Does this waste much…
jhabbott
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What's wrong with transporting a refrigerator on its side?

I tried to deliver a refrigerator and the customer saw that the refrigerator was lying down in the truck instead of standing up. He refused to accept it, claiming that the compressor would be damaged by having it on its side. I tried to explain…
0tyranny0poverty
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Why would a train automatically derail if a signal is passed at danger?

In a recent incident in London Network Rail said an empty train had travelled past a red signal, which resulted in an automatic derailment. No one was injured. [link] The derailment has caused quite a bit of damage, and a lot of travel disruption…
Gremlin
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Is there a method to determine the runoff for arid areas in developing countries?

Note: this question was totally rephrased and expanded on, addressing the comments and questions posed to the first version. The de-facto standard source for runoff calculations in South Africa is the "SANRAL Runoff Manual"…
SlydeRule
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Why does it take so long to restart a nuclear power plant?

I have heard a couple of times that an operating nuclear power plant which was shut down (non-emergency; e.g. for a regular check) needs over 24 hours (up to 72 hours?) to get up running again. Why does it take that long?
Martin Thoma
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How does width and thickness affect the stiffness of steel plate?

I have a 2 mm thick steel plate which is 300 mm long and 30 mm wide, supported at either end. It supports a weight-bearing wheel that can roll along the plate. It currently supports the maximum weight that I expect it to support when the wheel is in…
jhabbott
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Why do cars turn by turning the front wheel?

Why do we design cars to turn by turning the front wheel? Wouldn't it better to keep all wheels straight and turn by rotating the wheels on one side of a car more then the wheels on the opposite side of the car, like tank tracks do? That way you can…
Mustafa
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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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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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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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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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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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