# All Questions

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617 views

### efficiency and flow separation

I am studying about wind turbine and turbine. I have some questions, but first, I explain some cases as follow: Low velocity air over an airfoil at a zero-incidence angle does not initiate flow ...
575 views

### What is the strongest known *metallic* material which can be used on Earth?

The discovery of nanotubes and graphene has pushed the limit of material strength high enough that building a space elevator could be managable. But most of the new materials are created from carbon ...
8k views

### How to make smoke for a small wind tunnel?

I am making a small (desktop) wind tunnel for educational purposes, I want to have 10 fairly thick smoke-streams about 3cm apart. I have experimented with incense but the stream is not thick enough ...
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 ...
4k views

### How do I calculate the forces on a desk and its legs?

I have a design for a desk, and I'd like to not just guess at how strong it'll be, but I can't find an explanation on how to figure out all the forces involved that doesn't assume I already know a lot ...
433 views

### How is gas flow through (extremely long) pipelines monitored and controlled?

(This is closely linked with measuring the Mach number inside a nozzle but it is not regarding the supersonic flow) Friction and heat transfer have effects on the Mach number of the compressible flow ...
9k views

### How do train tracks handle really cold weather?

First of all, I'm interested in train track only, not the rolling stock. How are tracks built to cope with really cold weather? An example might be some place in Canada or Siberia. Ice would ...
669 views

### How do I use FEM to derive the torsional constant of an arbitrary shape?

In this question I ask about how to perform a first-principle derivation of the torsional constant of a section. It appears that there is no such analytical derivation for torsional constant, so my ...
1k views

### How do you model a real-life truss in structural analysis software?

I am trying to recreate the following model of a wooden roof truss provided to me by a truss manufacturer: My question is twofold: What is the common/correct way to model the boundary conditions and ...
216 views

### Hanging a steel mesh without significant deformation

I have an welded steel mesh, like in the following image. . Material: steel Diameter of the wires: 4mm Mesh: 15x15cm I found the following information about the welds: the minimal relative ...
677 views

### Velocity of flue gases through a pipe

I was wondering if there is any equation that helps to calculate flue gas velocity through a pipe? Can I use the Poiseuille Equation to solve this problem by assuming the flue gas is acting as a ...
20k views

### Physical meaning of shear lag [closed]

What is the physical meaning behind the concept of shear lag in fibre reinforced composite structures or the concept in general for any structure?
805 views

### How to secure a rotating disc so that it has no wobble

For a 3D printing application, I need to have a spinning disc(that I will rotate via geared stepper motors) that will wobble as little as possible. By wobble, I mean that it will only rotate around it'...
6k views

### What is Saint Venant Principle?

I am having problem with the application of Saint Venant principle.I have heard that quite often we use that knowingly or unknowingly.I would be very greatful to anyone who would explain this very ...
1k views

### Is the reliability of automotive sensor technology impeding the success of self driving car?

The reality is that sci-fi KITT is almost here. Recently I read articles Delphi car driving itself across the country as well as Tesla cars will be self-driving this summer. As of 2013 four states (...
891 views

### How to design a cooling chimney for a computer server?

I'm building a server type computer consisting of integrated motherboard, CPU, RAM and hard disk. There will also be a standard power supply unit. This is to be a Steam Punked computer, so... I ...
250 views

### How does a Levitron work?

I just watched this video: https://www.facebook.com/HigherPerspective/videos/1162007547164896/ I don't understand what I see. If the spinner's magnetic, the bowl is made of iron and that the wood ...
780 views

### Would a double helix spring be more or less effective than two springs?

Say I have a spring in the shape of the backbone of DNA. If I unwind the two parts which would have more potential energy when pushed all the way down, the double helical or both of the individual ...
60 views

### How can I calculate the power and torque required for the motor on a wheeled robot/vehicle?

How can I calculate the power and torque required for the motor on a wheeled robot or vehicle if a particular acceleration or movement up an incline is required?
6k views

### Why doesn't a lightning strike destroy the lightning rod?

Lightning strikes have been known to cause massive amounts of damage. The stats on a lightning bolt are: current levels sometimes in excess of 400 kA, temperatures to 50,000 degrees F., and speeds ...
23k views

### Would it make sense to have a 12V lighting circuit in a house?

Modern LED bulbs must convert the standard household supply (for example $240\text{V AC}$ in the UK) into a DC supply at a lower voltage (usually $12\text{V DC}$ I think) for the LED array. This is ...
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 ...
5k 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 ...
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 ...
515 views

### What are the lightest springs?

I am wondering if there is a spring strong enough and light enough to inflate an airtight membrane so that it floats at Standard Temp & Pressure. As an example, a 10cm cylinder would displace ...
14k views

### How much clearance does a car need when turning a corner?

I am contemplating buying a new car. However, the approach to the underground garage in my apartment has a 90 degree frustrating turn. Given the dimensions of the approach and car, what is the max ...
852 views

### How to determine the lateral earth pressure in a double-walled cofferdam?

The design of a retaining wall commonly involves determining the lateral earth pressure using either Rankine theory or Coulomb theory. Both theories involve mobilising the shear resistance of a ...
1k views

### How to calculate Power of motor when used as a generator?

How can you calculate how much power can be generated by a motor when used as a generator (like a motor used in a wind turbine)? Does the power depend on how fast the magnet is rotated? If so, is ...
375 views

### Why is “regular” gasoline standard instead of something more knock-resistant?

The standard light petroleum distillate for vehicle engines, "regular gasoline," is (or is equivalent to) some mix of heptane (C7) and octane (C8). Higher proportions of C8 are more knock-resistant, ...
3k views

### What is the difference between Bluetooth Low Energy and Bluetooth BR/EDR in Park mode?

It is known that Bluetooth Low Energy transmits data only during short time intervals called Connection Events. Connection events occur regullary with predefined period. The rest of the time Bluetooth ...
4k views

### Reading stepper motor datasheets to get torque and speed

I don't understand how to use the information in a stepper motor datasheet to understand how much torque it can generate. I was going to do a simple board and try to lift a small weight as an example ...
1k views

### Motor for a hydraulic pump in a hydraulic system

I am a complete beginner to hydraulic systems, and I've wanted to learn more about this area. I'm designing a hydraulic system that involves using hydraulics to push/pull objects using pistons. I have ...
14k views

### What do you call the difference between the on and off temperatures in a simple thermostat?

A simple thermostat will turn on at one temperature and off at a higher temperature. This keeps the thermostat from cycling on and off too quickly. The difference between these values is sometimes ...
996 views

### Can I weaken a coil spring consisting of spring steel?

I have a steel coil spring that is used by compression. It is too strong, and I would like to reduce its strength by some fraction, ideally keeping its length. Reducing it to roughly half would be ...
6k views

### Why are concrete bridges more prevalent than steel bridges in the United States?

According to the United States 2014 National Bridge Inventory the number of concrete bridges far outstrips the number of steel bridges. Reinforced Concrete: 253,336 Prestressed Concrete: 148,333 ...
1k views

### Large deflection of a cantilever beam with distributed normal load

I have a strip of stainless steel encastree'd at one end to which is applied a constant pressure on one side, and I need to know what the deflection equation y = f(x) is at equilibrium. If the ...
1k views

### Are there standard vibration and shock specs for shipment of a product?

Suppose I want to ship my product via UPS, or whatever other professional carrier service. What vibration and shock forces should I design my product to withstand? And how can I effectively test my ...
9k views

### Force required to empty a syringe

How would you go about solving the following problem. I believe Bernoulli's equation needs to be employed, but I'm not sure how. Find the magnitude of the force that needs to be applied to a piston ...
760 views

### Remote start on a car with manual transmission

I'm making a remote starter for a car using a Raspberry Pi. The problem is that the car has a manual transmission. The driver needs to remember to place the gear shift in neutral when parking, ...
6k views

### What method can I use to make a pivot point in an aluminum linkage?

I recently had a project where I made an aluminum linkage (similar to a scissor lift) operated by linear actuators. Aluminum pieces were fabricated from 6061 "standard" aluminum stock, 6mm (0.25 inch) ...
474 views

### Are smaller heat-pumps more efficient?

I was a doing a placement at a company, and they were designing a new heat pump. I was told the more compact you can make a heat-pump, the better it is for efficiency, and they mentioned something ...
1k views

### Truss manufacturer drawings unclear

I am currently looking at a set of truss layouts produced by our truss manufacturing partner for a residential building project. I have reason to believe these layouts are generated using Alpine (...
384 views

### Differential equation of the vertical displacement of a cable

Given a cable (totally flexible) fixed at both ends, subjected to a vertical force $f(x)$ in his plane, with variable area $A(x)$, and variable elasticity $E(x)$ I want to find the differential ...
1k views

### What is the densest ceramic?

I know ceramics are generally considerably less dense than pure metals or alloys but sand is used in barbells for its probably cheapness, user-friendly and easy availability but its a decent density ...
233 views

### mass calculation from transfer function or bodeplot

I have a double mass rotary model. The two masses are connected by an axis which together acts as a spring damper system of the fourth order. The system is actuated by a motor and the angle of ...
2k views

### Involute Gear Calculation

I've written a program to generate gears and write them to dxf files. I thought all was well until I looked at the mesh of two gears. From everything I've read there should be no backlash when the ...
66 views

### What diameter of particles will result in a blocked borehole?

My mine is looking to install a 600 mm open borehole to drop particles up to 150 mm through. It's a 320m shaft to drop ballast down to save time compared to using the drift. When it gets blocked ...
1k views

### Why do bluetooth headsets get interference (choppy sound quality) outdoors?

This is more of a general physics question to help me understand how to choose sports headsets in the future, however it is too specific to a certain use case (bluetooth headset) to belong in the ...