NMech
  • Member for 2 years, 10 months
  • Last seen this week
Why are railroad tank cars bent in the middle?
Accepted answer
51 votes

As other have pointed out, the main utility is to allow easier cleaning of the tank cars from sediment (solid precipitates). Usually, there is a drain in the lowest point. The reason that it is in ...

View answer
Why are engine blocks so robust apart from containing high pressure?
Accepted answer
44 votes

If you consider only the static forces then indeed the thickness might seem over-engineered. However, engine blocks are not statically loaded. They operate in the range of a few hundred to a few ...

View answer
How does turning off electric appliances save energy
Accepted answer
35 votes

Electricity production optimization is a very complex subject. It is also affected by many parameters , which I will try to outline below. TL;DR: Demand is constantly monitored and supply is ...

View answer
Why exactly does a washer help distribute the stress around a bolt?
Accepted answer
33 votes

I will expand on DKNguyen answer, because to my knowledge also the two reasons are: reduce contact/bearing stresses (having a significant effect on thin finishes live galvanisation) change the joint ...

View answer
Why does light bend after travelling half of the lens?
Accepted answer
26 votes

It changes on both E and the exit point of the beam (see image below). source My understanding is that refraction occurs at any boundary that there is a change of the wave propagation velocity. The ...

View answer
Why does "potential energy" have the word "potential" in it?
26 votes

Because it has the potential to produce mechanical work.

View answer
How do vending machines prevent people from stealing goods?
Accepted answer
24 votes

The vending machines have different product delivery box implementations. One of the most common ones -I've encountered- is the following: Basically you have a box which has an opening, as shown in ...

View answer
How do suction cups work?
Accepted answer
24 votes

TL;DR: Its not the air that's enclosed inside that creates the force, but the lack of air - or more precisely pressure. First of all some nomenclature (this is for the closed type, there is also the ...

View answer
Why does a gear have extra holes?
Accepted answer
23 votes

Different gears have different drivers for having holes. One way you can categorize gears is by whether they are used primarily for transferring: motion: transferring angular position and angular ...

View answer
What unit of weight is that?
Accepted answer
21 votes

You are probably right (it being of Russian origin). The weight seems to be 5 funt. 1 funt is the Russian equivalent of a pound. It is written as Фунт, funt, and around 1900 it was the basic unit of ...

View answer
Why does a jumping rope have no bending stiffness and compression stiffness?
Accepted answer
17 votes

TL;DR: The bending and compression (buckling) stiffness is so small because the second moment of area of the fibres is small. Bending stiffness It does have a bending stiffness however it is really ...

View answer
How do ball bearings not crack from a load concentrated on an infinitesimally small point?
16 votes

TL;DR: ball bearings deform due to Hertzian pressure and therefore distribute the load However, the reason balls (rolling elements) don't easily crack is the ductility of the material (and to some ...

View answer
What is the physical reasoning behind metal becoming stronger and harder if heat treated?
14 votes

In short the heat treatments in steel change the phase of iron between the following phases: Austenite Cementite Martensite Bainite Ferrite Perlite. (Actually quenching does not allow low ...

View answer
Can gravity be a driving force for a spring-mass system?
12 votes

It really depends on the problem and what you want to capture. Usually, in classes, it may be beneficial for the students at an initial stage to disregard gravity alltogether in order to simplify the ...

View answer
Brittle = highly stiff but not very strong
11 votes

IMHO there is an "misuse" of the words brittle/strong/stiff that the OP is using. My interpretation of brittle has to do with sudden failure during testing with little to none plastic ...

View answer
What kind of metal are eye glasses frames made from?
Accepted answer
11 votes

There are many different materials that can be used for modern eyewear. Based on the following table (I put it together from online searches, its not from a single site, although the content is ...

View answer
Is cast iron better that Copper or Aluminum for cooking steaks?
11 votes

UPDATED TL;DR: Cast iron has the advantage, because it has a greater capacity to hold heat, and because of its lower conductivity it releases it more slowly, thus its temperature does not fluctuate as ...

View answer
Why does corrosion take place at certain stressed regions?
11 votes

One of the mechanism that affect corrosion is known in the literature as Stress Corrosion Cracking (SCC). The idea is that tensile stressed regions are prone to crack development. Crack development ...

View answer
Unknown circuit component with glass encapsulated contacts
Accepted answer
11 votes

It looks to me like a reed switch (I can't be really sure though because the image is not clear enough). A reed switch is an electrical switch operated (usually) by an applied magnetic field. A ...

View answer
What happens from B to C in this stress strain diagram of mild steel?
Accepted answer
10 votes

One point of note is that the yield region is not as cleanly defined as BCD is in the image (although most books have it that way). In reality the yield region looks like The following image is one ...

View answer
How does a (pulley based) continuous variable transmission (CVT) work?
Accepted answer
10 votes

Review of geared transmissions In general, the idea of a geared transmission is depended on the gear ratio. The gear ratio $i$ affects many aspects of a gear transmission, and the following equations ...

View answer
When a car with an open differential turns, why does the inner wheel slow down and the outer wheel speed up?
9 votes

TL;DR: The kinematic constraint imposes the redistribution of forces on the four wheels. This redistribution is permitted due to the car differential. IMHO it is easier understand this if you first ...

View answer
Is the main goal for wind turbines to take maximum energy for a given diameter?
9 votes

The function of the wind turbine is to extract as much as possible energy from the moving mass of air. The energy of a mass $m$ of air is $$KE = \frac{1}{2}m v^2$$ and the power is (because the mass ...

View answer
Aluminum weight saving
9 votes

TL;DR: Materials perform differently under different loading conditions. Some applications are more suited for steel others for aluminium I will try to give another more general perspective/approach, ...

View answer
Unit of "cN.m" used on torque wrench
Accepted answer
9 votes

100 cN.m are 1 N.m The c before the N.m is pronounced centi. It's a standard SI prefix. 1 c of a unit is $\frac{1}{100}$ of a unit. Therefore to convert toN.m you need to multiply cN.m with 0.01. $$...

View answer
Why does temperature not increase by putting more logs into the fire
9 votes

I agree with Chemodynamics, and I will try to add a different perspective (or maybe two). The fire process is a process where you add a fuel (i.e. energy in the system), and that fuel is gradually ...

View answer
Mechanical Advantage of 3 Pulley System
Accepted answer
9 votes

The tension on the rope is everywhere the same and its equal to F. So if you did a free body diagram on the following system by sectioning along the ropes: what you get from the equilibrium is $4F =...

View answer
What is the accepted way to write units when specifying multiple dimensions?
9 votes

I 'll start with the one that you should DEFINITELY NOT use: $mm^3$ or $mm3$. Probably the most widely used is the 1st. It's compact and economical and these are two of the most deciding factors in ...

View answer
Why are train brakes so complicated?
8 votes

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 ...

View answer
How much power does it take to supply a laser which delivers 100 watts?
8 votes

The total electrical to optical power efficiency of a laser system is sometimes termed wall-plug efficiency. It is the ratio of $$\eta = \frac{\text{optical output power}}{\text{consumed electrical ...

View answer
1
2 3 4 5
29