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17
votes
3answers
6k views

What is the most efficient means of warming a building with a high ceiling?

Consider a large auditorium, a church, or some other very large, essentially one roomed building with a high ceiling. Suppose that the building has many entrances which enable cold air in/hot air out ...
17
votes
1answer
3k views

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 ...
17
votes
1answer
1k views

Fracture patterns in tempered glass

While browsing a local news site, I stumbled upon this picture of a broken bus door. The glass was fractured due to a rock impact. As far as i know there are no heating elements on the window section ...
16
votes
6answers
8k views

What limits the speed of a car?

From an engineering perspective, what limits the maximum speed you can reach with a regular car? I understand that some of the faster cars are for safety reasons limited to not run faster than say 250 ...
16
votes
8answers
22k views

How to stop water flow in a siphon?

I have assembled a small DIY drip-irrigation system for my terrace garden. Please have a look at the attached image. I switch on a small pump to start the drip-irrigation system and then switch it off....
16
votes
1answer
54k views

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 ...
16
votes
5answers
822 views

Meshing of complex geometrical domains

When using the finite element method, I have always used either already meshed domains or very simple ones. From what I've heard, meshing complex geometries is often outsourced to specialized ...
16
votes
1answer
3k views

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 ...
16
votes
1answer
646 views

Can we change steel properties by application of magnetic field while quenching?

Austenite is non magnetic while $\alpha$-ferrite and pearlite are magnetic. (Magnetic properties of pearlite vary as a function of carbon content) If a strong magnetic field is applied in a ...
16
votes
1answer
2k views

How to design a house to be cooled passively? [duplicate]

I live in Louisiana these days, in an area that is known for its numerous antebellum plantation homes (circa early 1800s). While touring one of these homes it was clear that almost everything about ...
15
votes
14answers
25k views

What kind of math do engineers really use? [closed]

I am from the mathematics StackExchange section, many of my students are engineering students at University. I was wondering what kind of calculus do you real engineers use? I have known two engineers....
15
votes
5answers
7k views

Does an electric vehicle going downhill recover energy?

I have to model the behavior of an electric car. For this, I use these equations and I can observe by "playing" with parameters that, when going downhill at constant speed, the car has a negative ...
15
votes
3answers
26k views

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 ...
15
votes
3answers
30k views

Can wifi signal reception be improved by opening a door?

A wifi user is in a different room than the router. The computer is having a hard time connecting and receiving the wifi signal. Can the wifi signal from the router to the computer be improved by ...
15
votes
10answers
270k views

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{...
15
votes
4answers
22k views

What material is used to hold molten iron in a furnace?

When iron is melted, I guess it has to be transported and contained. I think the container in which it is has to be able to withstand higher temperatures than what you want to melt. According to this ...
15
votes
3answers
2k views

Why is it more reliable to use the land/pit transition in a CD-ROM?

I was reading about how CD-ROMs work and I came to this: Although it might seem simplest to use a pit to record a 0 and a land to record a 1, it is more reliable to use a pit/land or land/pit ...
15
votes
5answers
4k views

When do I need to consult a professional engineer during a home renovation?

I am a homeowner who likes to save money by performing DIY work. When possible, I prefer to serve as my own general contractor to reduce the cost of a project. However, when I talk with professionals ...
15
votes
4answers
4k views

Why does the microwave plate start in a random direction?

...or what type of motor is used there? I found this type of motor - usually powered with low-voltage AC (~12V), but at times with 230V, in several appliances that require very slow rotation and ...
15
votes
3answers
3k views

How does measurement uncertainty combine with tolerances?

Given a tolerance within which your workpiece should be manufactured, say some length should be $10\pm1$mm. If you determine that your uncertainty in measuring this length is $0.2$mm (at 95%). How ...
15
votes
2answers
6k views

How do I size metal plates to get the correct dimensions after folding?

I am designing a metal plate that will be laser-cut (or machine-cut) and then folded. I want to know how to size the pre-folded plate in order to get the right dimensions after folding. My actual ...
15
votes
5answers
2k views

Why don't refrigerators have parts outdoors?

I've always wondered why refrigerators don't have some of their parts located outdoors like an air conditioner. In warm weather, it seems like it would make sense to have the condenser outside like ...
15
votes
2answers
482 views

What is the physical interpretation of the second term in the viscous stress tensor in the Navier-Stokes equations?

I have been searching for this answer for awhile. I've read numerous texts and even watched some lectures online, but often times this is never explained and just given. The viscous stress term in the ...
15
votes
2answers
6k views

While going downhill, does my car consume less fuel when in neutral or in gear?

I once meditated on the fact that a car, in downhill, would consume more fuel when in neutral to keep the engine on, rather than in gear. To keep the engine on when in gear, in fact, you mostly need ...
14
votes
4answers
3k views

If the emergency brake in a train is broken, do the passenger car brakes still work?

Scenario: Suppose the emergency brake button in the cab of a train is not working. Would the emergency brake cords / buttons in the passenger cars still work? This question is inspired by this ...
14
votes
3answers
644 views

Do solar cells age? Why, and how?

As I heard, the life expectancy of photovoltaic cells is normally some decades, as so. This is very long, regarding their high cost, it has significant (negative) effect on the total costs. Why do ...
14
votes
7answers
19k views

Is stainless steel plating possible?

Is there a method for plating steel with stainless steel? If so, is it chemical, electrical, or electrochemical? I did a quick search on the internet but was unable to find a service. I'm ...
14
votes
2answers
3k views

What is this small rotating part from a cell phone?

What is this tiny rotating piece of hardware that I found inside my Samsung GE1202? It has E9C written in blue on it.
14
votes
2answers
2k views

How should I position two shelf supports for the best distribution of load?

I'd like to mount a shelf on the wall. I have two shelf supports to do so, like this: Relative to the shelf, where do I place the (blue) supports to achieve the best distribution of load?
14
votes
4answers
1k views

How should the public raise questions about unsafe structures in the United States?

In a program on NPR that I was listening to, there was a bit about a bridge that from the description sounded to a layman as unsound and is still in use. The program described it as an old wooden ...
14
votes
2answers
6k views

If aircraft are pressurised, why do our ears pop during liftoff and landing?

Something hit me during my last flight: our ears feel that the pressure around us changes quickly during liftoff and landing, they hurt more and more until we make them pop. However, the cabin must ...
14
votes
3answers
5k views

Can I use a ultrasound sensor to measure water level?

If I use an ultrasonic sensor will it detect the water level? I was thinking about a product to read water level on water boxes (common in Brazil). I researched about instrumentation for this ...
14
votes
2answers
516 views

Why are lasers used for concentrated light applications instead of incoherent light sources?

Some laser applications consist simply of concentrating light into a small spot. Two example applications are laser welding and cutting. In these cases a CO2 laser is often used which needs a ...
14
votes
1answer
489 views

What limits a power plant's load gradient?

Each power plant has a load gradient characteristic, describing to what extent it can change the output of its generators in a given timeframe. Reading the literature, I know that, for example, a gas ...
14
votes
3answers
189 views

Looking for best material for a cryogenic ball mill cup and balls

I am working with a set of alloys that must first be ground up in a ball mill at cryogenic temperatures. It is important that no contamination makes it into the material and careful steps are taken to ...
13
votes
4answers
15k views

Why is oil used as the lubricant in power generators, while water is the most available, cheapest and accessible lubricant?

The lower viscosity of water reduces friction. Besides, the water can transfer heat way better than oils. So why not use water as a lubricant in wind or hydro turbines, especially on equipment which ...
13
votes
3answers
6k views

Why does moving air feel cold?

I'm taking a thermodynamics class and had the following question. I was going to ask my professor directly, but it seems like a stupid question with a simple answer, so I thought I'd try my luck here ...
13
votes
3answers
584 views

Are pontoon bridges being considered to extend bridge span?

Pontoon bridges differ from traditional bridges in that they are supported not by structures anchored to the floor of the body being spanned but by floating pontoons that are connected by a more rigid ...
13
votes
5answers
667 views

Are pneumatic tires obsolete?

Adaptive suspensions with adjustment rates on the order of milliseconds are going mainstream in consumer vehicles. Air suspensions have been common on commercial trucks and some SUVs for some time. ...
13
votes
1answer
3k views

From an engineering standpoint, what is the purpose of the indent in a coffee lid?

I've see the same lids every day but I never really thought about their construction. There is an indent in a "Solo Travel Lid" for coffee cups that is just above the hole that you drink the coffee ...
13
votes
2answers
2k views

What is this Y-shaped screwdriver bit, and what is its purpose?

I found this strange looking bit in a bit set of uncommon bits, including Security Torx, hexalobular, tri-wing, spanner head, 12-point flange, Torq-set and others. It's the only one that I could not ...
13
votes
3answers
12k views

What is a Spiral Curve, and How is it Different from a Normal Curve?

I've heard the term spiral curve used to describe a section of highway that is more aesthetically pleasing to the driver's eye. However, I believe I've driven on enough road to say that I can't ...
13
votes
3answers
3k views

What happens when you put the wrong type of fuel in an internal combustion engine?

What happens to the working of petrol engine when it is emptied and filled with diesel or to a diesel engine emptied and filled with petrol? Will the engine be able to operate and, if not, why not?
13
votes
2answers
162 views

Do “analog FPGAs” exist?

I am thinking on analog circuits, whose circuit design could be read (or, at least, significantly altered) from software. Do they already exist?
13
votes
3answers
461 views

I have inherited a product with inconsistent designs sharing the same part number. What do I do?

I am now in charge of a product line my company has been shipping for a decade. One of the previous product engineers was... shall we say, less than conscientious about sustainability and proper ...
13
votes
3answers
948 views

Do I need to worry about galvanic corrosion when inserting a steel bar through aluminium?

My design uses a round steel bar inserted through a hole in an aluminium component with a tight fit (no movement). The operating environment is dry, 20-40°C. Do I need to worry about galvanic ...
13
votes
2answers
6k views

How does a multimeter protect itself from high voltages?

I have used a cheap multimeter to measure voltages in simple DC circuits, but I have seen pictures of them plugged straight into the mains and used to measure various home-built generators. Why doesn'...
13
votes
5answers
2k views

Are there any materials known to be sound-insulating but thermally-conductive?

Are there any materials known to be sound-insulating as well as thermally-conductive? Cost is not an overriding concern, but preferably costing "reasonable amounts" and much less than national ...
13
votes
7answers
8k views

Why is air pressure in all directions?

Here is a typical definition of air pressure: Air pressure is caused by the weight of the air molecules above. Even tiny air molecules have some weight, and the huge numbers of air molecules that ...
13
votes
1answer
332 views

Estimating whether the flow through a valve or nozzle cavitates

My understanding is that cavitation occurs in the flow of a liquid when the static pressure drops below the vapor pressure, even intermittently. So even if the time-averaged static pressure (what you ...

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