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1500 questions
12
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1 answer
What causes rechargeable batteries to age? What can be done to extend life of these batteries?
These days most of modern electronics use rechargeable batteries as a power source. Also, these days most modern rechargeable batteries are Lithium Ion or Lithium Polymer based. Like any other devices, over time these rechargeable batteries lose the…
Mahendra Gunawardena
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4 answers
Is interference between aircraft an issue for fly-by-wireless technology?
I was reading up on fly-by-wire development, and I saw a short section about fly-by-wireless technology. It seems like a great idea, with the potential to lower costs, weight and complexity. I can see a possible scenario where it could be an issue,…
HDE 226868
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5 answers
Why are most standard bolt threads single start?
When looking at thread descriptions, one of the basic properties is always the number of thread starts.
As far as I could tell, all of the major standard bolt threads are single-start. This includes:
Unified Standard (UNC, etc.)
National Pipe…
hazzey
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12
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4 answers
Would an object at the bottom of the sea still experience buoyancy?
So I understand that buoyancy happens because the fluid exerts larger amounts of pressure from beneath an object compared to above, like in this picture
So my question is, what if the object is forced to the bottom of the container, so that no…
M. Wother
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At what point does an I-beam becomes a H-beam?
According to BS5950, a beam section can be classified as plastic, semi-compact, compact or slender. For the same section area, a H-beam can take axial compression (without buckling) better than an I-beam, and as such, uses a different strut curve in…
Question Overflow
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Why was Freon used in spray cans before it was declared a threat to ozone?
I've heard that in the past, spray cans (aerosol cans) contained Freon. I found that the Montreal Protocol made the usage of Freon illegal due to its effect on the ozone layer, but I can't find the reason for why Freon was used in the first place. I…
Physther
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5 answers
Determining Drill Speed
How are spindle speeds calculated for a drill bit?
I've seen dozens of charts that highlight the rpm that should be used for specific drill bit types, bit diameter, and material. However, what if my chart doesn't have the particular type of material…
Justin Trzeciak
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6 answers
In Engineering fields, how often do you find yourself being asked to be a "salesperson", and what is your reaction?
I have recently been told that my "salesmanship" is lacking when it comes to getting my ideas implemented. I receive the feedback that my ideas are sound and the data to implement is compelling, and even that the ideas are presented in a way that…
Tim D
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1 answer
How do I batch plot drawings in monochrome without editing DWG?
I'm using AutoCAD 2015, and I run into this all the time. I'm given a group of DWG drawings, and I want to plot them into one monochrome PDF, but they do not have monochrome.ctb selected as the plot style. Is there any way in Batch Plot to publish…
Ben Miller
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Why do we use multiple reinforcing bars instead of one bar with a big diameter in reinforced concrete?
Why do we use multiple reinforcing bars instead of one with a big diameter in reinforced concrete?
Does increasing the number of reinforcing bars means that the reinforced concrete will have a higher tensile strength?
M. Kawa
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3 answers
How different is using styrofoam rather than empty cans when pouring concrete?
In the recent 6.4 earthquake that hit Taiwan, it was seen in a newswire photograph of rubble that metal cans were embedded in the concrete.
The quote from an official regarding this practice:
For such purposes in construction, it was not illegal…
user348
11
votes
4 answers
What is the difference between "Crushed Stone" and "Crushed Gravel" aggregate?
Crushing Question
While reading a material specification for crushed aggregate, the text mentions both "crushed stone" and "crushed gravel" are acceptable. These materials sound very similar, but they are mentioned individually. I assume that this…
hazzey
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4 answers
Why were engineers negligent in the 1981 Hyatt Regency walkway collapse?
I was recently reading up on the 1981 Hyatt Regency walkway collapse. It was a tragic loss of life and haunts many to this day.
The linked article does a better job of summarizing things, but here's a summarized version of what led up to the…
user16
11
votes
3 answers
Should I reject a concrete mix design for having too high of a compressive strength?
I usually design precast concrete members for the common concrete strength of f'c=4,000 psi at 28 days. Occasionally, a mix design will be submitted that has a very high strength. In one case, the mix that was submitted had a history of cylinder…
hazzey
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2 answers
Buckling: Do buckling mode shapes of n > 1 occur in reality?
In the buckling of columns we know that:
$$P = \dfrac{n^2\pi^2EI}{L^2}$$
The smallest value of P occurs when $n=1$ which gives a simple buckling shape (one wave):
$$P_{cr} = \dfrac{\pi^2EI}{L^2}$$
However for $n > 1$, as shown below the buckling…
pauloz1890
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