114
votes
Why do glass windows still exist? (Why haven't they been replaced by plastics?)
There are two main reasons why glass is still preferred over say PMMA.
The first is durability. As long as it isn't broken, the glass in a window can easily last for hundreds of years in good ...
- 15.1k
46
votes
Why do glass windows still exist? (Why haven't they been replaced by plastics?)
Here is a plastic (most likely PMMA) window, in a boat, after only 37 years.
In addition to the obvious scratches, the outer surface has developed a cloudiness : possibly from degradation due to ...
- 1,610
31
votes
Why do glass windows still exist? (Why haven't they been replaced by plastics?)
What are the requirements for window glass?
Resistance to moisture
Resistance to UV radiation
Resistance to cleaning agents
Very high transmission in the visible spectrum
(There are many more, from ...
- 1,618
30
votes
Accepted
Which is Worse: Car vs. Car or Car vs. Wall?
From the point of view of the driver of a car, impacting another car is about as bad as crashing against an ideal wall (a wall with zero deformation whatsoever).
If there were a plane reflection ...
- 416
30
votes
Accepted
Why would a train automatically derail if a signal is passed at danger?
Firstly, the incident happened as the train was leaving a siding passing a shunt signal. These provide less authorisation than a normal signal does, even when they are not at danger (the train can ...
- 416
25
votes
Accepted
Why would you launch a large ship by dropping it sideways?
A specific reason for doing this is simply when there isn't enough room to do a bow or stern first launch. This is often the case when a ship or boat is built in a yard on a river or canal either ...
- 15.1k
21
votes
Why would a train automatically derail if a signal is passed at danger?
While I'm sure it caused less damage than a train collision
Exactly. This is a last-resort response intended to avoid a full-on collision.
A derailed train causes some damage and is a mess to clean ...
- 11.3k
15
votes
Why do glass windows still exist? (Why haven't they been replaced by plastics?)
I actually did make windows out of plexiglas for an outbuilding. I could work them to the shape I wanted and they were lightweight. However, I discovered that they indeed scratch easily: just trying ...
- 257
13
votes
What is this locking pin for a hinge called?
That is a ring-grip quick-release pin, sometimes referred to as clevis pins. McMaster link
- 2,347
11
votes
My customer wants to use my products to do something unsafe. What is my ethical obligation?
Almost every manufactured product can be abused in an unsafe way by a creative enough user.
If the customer asked your opinion on doing something which is evidently unsafe, I would suggest (on the ...
- 12.4k
11
votes
Which is Worse: Car vs. Car or Car vs. Wall?
In the limit of the cars being identical and the wall being immutable, I would argue that the two situations are the same based on symmetry.
Consider the collision of the two cars with no wall. ...
- 6,386
11
votes
Why would a train automatically derail if a signal is passed at danger?
Why derail?
If the train went past a red signal, then all of the other safety systems already failed! The method of last resort is to make absolutely sure that the train will not travel down the track....
- 10.6k
10
votes
Why do glass windows still exist? (Why haven't they been replaced by plastics?)
After some research,
we are using glass windows as it was used traditionally. Actually plastic windows exists. Though it may take time for most of us to adapt to it.
While the reasons to consider ...
- 585
10
votes
Accepted
Is it safe to drop a bomb?
In general a modern commercial/military explosive device will not explode if dropped. The most common commercial/military explosives such as C4, TNT, ANFO are catagorised either as Secondary or ...
- 2,631
10
votes
Why are train brakes so complicated?
This answer addresses the following sentence:
So I'd expect to see the brakes applied by a spring that is capable of stopping the wheels of a fully loaded car, and a single-acting cylinder that works ...
- 24k
10
votes
Why are train brakes so complicated?
You need to consider what happens if a hose bursts, and your spring-applied brake locks the wheels on one or more cars - how do you get that train back to the depot? There could be a manual brake ...
- 451
8
votes
Accepted
Will lightning strike an aluminum rod in a pot on my balcony?
xkcd has a fantastic description of how lightning works. This video is also quite good (especially as of 0:56, but the rest is worth watching as well) since it shows lightning in super slow motion, so ...
- 13k
8
votes
What drives improvements in seismic safety?
This is a pretty huge topic, but I can summarize a couple major factors.
More population, more damage, more awareness
The effect of a disaster that kills thousands of people and causes property ...
- 3,211
8
votes
Accepted
How are blanking spades entered into gas pipelines?
The most straightforward way would be to mount them between flanges, after a section of pipe has been valved off and flushed.
This is correct. Blanking spades, also known as slip plates, slip blinds ...
- 533
8
votes
Why do car-seats have an expiration date?
It's a combination of 1, 3, 4, the product development cycle, and the nature of the product.
1 - Damage in materials is a cumulative process, the product of hundreds or thousands of little events (e....
- 2,135
7
votes
Why do glass windows still exist? (Why haven't they been replaced by plastics?)
Another issue is that the coefficient of thermal expansion of many plastics is higher than that of window glass. Frames for plastic windows would have to be able to accommodate more expansion / ...
- 71
7
votes
Why would a train automatically derail if a signal is passed at danger?
Why would a train automatically derail if a signal is passed at danger?
When the cost of derailment is lower than the cost of a train collision, and the possibility of train collision exists, then a ...
- 1,116
6
votes
What is the difference between being UL recognized and being UL listed?
Products can be given a UL Listing Mark or the can be classified as a UL Recognized component. The simplest way to think about the difference between these two is that a UL Listing Mark is meant for ...
- 360
6
votes
Accepted
Will PVC build up an electric charge and cause a spark?
I am skeptical as to whether this component needs to be grounded at all; it's not conductive, so my intuition is that it isn't able to cause a shock.
My question is basically (1) can a PVC pipe cause ...
- 3,587
6
votes
Which is Worse: Car vs. Car or Car vs. Wall?
I'm guessing you haven't seen the Mythbusters episode on this.
Then, see this writeup that explains why they are correct, since Mythbuster's explanation leaves something to be desired.
In short, it'...
- 160
5
votes
Which is Worse: Car vs. Car or Car vs. Wall?
The answer will depend on the wall, and on the other car.
Consider the comparison to an ideal, immovable wall. In the case of a hypothetical collision between a Humvee (2500 KG) and a VW Beetle (850 ...
- 282
5
votes
How does one define 'safe' in engineering?
A common refrain in these kind of discussions is "there is no such thing as safe, only safer." Nothing we make is perfectly safe in an absolute manner - we don't design buildings to withstand asteroid ...
- 4,511
5
votes
Accepted
How does one define 'safe' in engineering?
For something to be safe there must be no risk of injury, harm, disability or death to anyone when something is being assembled, used or in the future as a result of the something being used. Where ...
- 9,527
5
votes
My customer wants to use my products to do something unsafe. What is my ethical obligation?
I have tried, but have not found a way to respond to this question that is not opinion based. By their nature, a person's ethics are just that; a person's ethics. They are usually deeply held, ...
- 51
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