# Engineering Stack Exchange Community Digest

## Top new questions this week:

### Why does this thing that is not a screw have a screwdriver slot?

I am (partially) disassembling an old sewing machine to clean it up. While removing the bobbin winder, I found this thing that has a screwdriver slot, but it isn't a screw. This is the part: It came ...

mechanical-engineering mechanisms mechanical
 answered by Jonathan R Swift 1 vote

### Why do we always need to calculate the 'Moment of Inertia' about neutral axis for bending?

I was having a look at the bending stress derivation in few of the books. The derivation indicates how each of the element in the bending stress equation is derived into that equation. However, for ...

statics solid-mechanics bending

### What's this tool?

This isn't mine, but I own one of these and I have no idea what it is. With the spike attached it looks like a marking gauge of some sort.

tools

### How are ships stacked ontop of other ships?

As shown at this skeptics SE post, there are ships that carry other ships as cargo, etc... My question: how are the ships stacked onto the flat bed ship? Is there some kind of specialized crane that ...

civil-engineering transportation ships

### How are bode plots drawn for unstable systems with time delay?

All the example of bode plots I see in textbooks are of stable systems without delay. I wanted to know if bode plots can be drawn for unstable systems with time delay. Using the usual method to draw ...

control-engineering control-theory

### How to estimate effective area of contact between rough surfaces as function of surface roughness

The engineering problem that I am trying to solve is the following: I have two elements of a magnetic circuit that I must keep in contact through threaded fasteners. The primary objective is to ...

structural-engineering design bolting

### When is a convex weld finish required?

In weld symbols one can specify the finish of the weld. In flush weld, for example, one needs to level the weld into a flat surface. I can imagine when this is needed: if something is required to rest ...

welding welds
 asked by S. Rotos 1 vote

## Greatest hits from previous weeks:

### What does "a" mean at the end of a refrigerant's designation (R-134a)?

I was studying the designation of names to refrigerants. The following is the basic formula: R - (m - 1) ( n + 1) ( o ) where: m = number of carbon atoms in the refrigerant n = number of hydrogen ...

chemical-engineering refrigeration

### How does turning off electric appliances save energy

We all know if we use less electricity we save energy. But the energy we're getting is result of burning (not necessarily the literal meaning) the fuel. Even if we don't use that energy that fuel is ...

power energy power-engineering fuel-economy

### What angle - for a strut - provides the greatest vertical strength/support for a cantilever?

I want to affix a cantilever to wall. I will support the other end of the cantilever with a strut made of wood, that attaches to some point on the wall below the cantilever, as shown in this sketch (...

structures statics stresses wood

### What does "$\pm$ 0.5% F.S." mean?

I've seen it in several data sheets - it is a measure of error of some kind, of course. The problem is I dont know the exact meaning. I've seen it in the context of repeatability, accuracy and ...

nomenclature

### What is the meaning of vorticity and circulation?

In fluid kinematics I can't understand the meaning of these terms : vorticity and circulation. Can somebody give me a description of these terms so that a lay person can understand them easily?

fluid-mechanics

### How to determine whether plastic is ABS or Polypropylene?

I have a pump that I want to use to pump a solvent. It is hard black plastic so I'm pretty confident it is either ABS or polypropylene (it wasn't expensive enough to be some more exotic plastic). My ...

plastic

### What is the difference between grout and mortar?

As I know so far, mortar and grout are mixtures of cement paste and fine aggregates, but both of them play different roles in the construction site. Is it true that grout has more strength compared to ...

materials civil-engineering

## Can you answer this question?

### Why is a throttling valve isenthalpic whilst a nozzle is not?

From my understanding, Nozzle's and throttling valve are devices which both trade pressure for velocity, so they increase velocity at the expense of having to decrease the pressure. If we examine ...

fluid-mechanics thermodynamics pressure temperature