Questions tagged [mechanical-engineering]

Questions within the problem domain of mechanical engineering. Mechanical Engineering can be a broad field; consider choosing more specific tags if they apply.

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43
votes
9answers
8k views

Is it possible for a bicycle chainwheel to have a fractional number of teeth?

Background In the world of bicycle motocross, also known as BMX racing, gearing is a hotly-debated topic. Since the bikes are all single-speed, gear ratio is a fixed number defined as ...
35
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2answers
16k views

What is the purpose of these diversions in a natural gas line?

The campus where I work has a long covered walkway (~.5 mile) which has several labeled pipes running under the roof (chilled water, fuel oil, air...). All of the pipes run dead straight except for ...
28
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3answers
8k views

Why are railroad tank cars bent in the middle?

I recently noticed that the cylindrical shape of a railroad tank car is not completely straight but has a bend in the middle. The entire tank is a bit lower there. What's the reason for this bend? ...
28
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10answers
7k views

Is it possible to build an air compressor with no moving parts?

Is it physically possible to build an air compressor with no moving parts? I'm envisioning a thermodynamic cycle capable of compressing air with no moving parts and operated in a stationary way. There ...
25
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4answers
3k views

How are increasingly accurate machines made?

Making extremely accurate machines seems like a chicken and egg problem. How do you make one if you don't already have one? For example, how was the first indexing head made without an indexing head ...
24
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5answers
5k views

Why are engine blocks so robust apart from containing high pressure?

Lately, I've been pondering why some engine blocks are so bulky, I always thought intuitively it was because they had to last a long time whilst containing thousands of combustion cycles but the more, ...
24
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4answers
23k views

Why do hydraulic systems use special fluid - what's wrong with water?

As a hydraulics layman thinking about hydraulic systems, it seems that the important factor is to have a liquid that doesn't compress much or at all. Doesn't water meet this requirement, and what ...
24
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3answers
85k views

Calculating pitch, yaw, and roll from mag, acc, and gyro data

I have an Arduino board with a 9 degree of freedom sensor, from which I must determine the pitch, yaw, and roll of the board. Here is an example of one set of data from the 9-DOF sensor: ...
23
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8answers
10k views

Why are rear wheels not placed at the extreme rear of a bus?

In some cars, I have noticed the rear wheels are located at the extreme rear of the vehicle. However, I have noticed that the rear wheels of buses are always located about 1/4th of the way forward ...
23
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5answers
7k views

Why don't hydroelectric plants use cascades of turbines instead of single turbines?

In a gas turbine engine there're multiple sets of blades - one set after another and combustion products pass all the sets and each set of blades gets some of the power. This increases utilization of ...
23
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2answers
5k views

Why would you launch a large ship by dropping it sideways?

I'm referring to the process shown in this video: https://youtu.be/Quyr5R1Rbfw?t=20 Or this image from Wikipedia: In it, a large warship is launched into the water by essentially dropping it ...
22
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6answers
13k views

Why do car wheels have holes?

If you have a look at the car's wheels, you'll notice that they have holes which can be of different forms (mostly circular or rectangular). Why do they have such holes? Doesn't that reduce the ...
22
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4answers
7k views

What is a reason that handlebars fit to a motorcycle and steering wheel fit to a car?

What is the reason that handlebars are installed on motorcycles and steering wheels are installed on cars? Notice that the way to use both handlebars and steering wheels are quite similar, but a ...
20
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1answer
71k 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 ...
20
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1answer
458 views

Sizing a pressure safety valve for two-phase flow

I understand that valves in two-phase vapour / liquid were sometimes sized by considering the required vapour and liquid flow rates separately, and then adding the results together. But this is now ...
19
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3answers
5k views

Windmills in empty fields. Why no trees?

I have noticed that windmills are generally built in empty fields with no trees around, and I've been wondering why... A windmill is generally way taller than trees and I can imagine that trees don'...
17
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3answers
37k 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 ...
17
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10answers
343k 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{...
17
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2answers
32k views

How does width and thickness affect the stiffness of steel plate?

I have a 2 mm thick steel plate which is 300 mm long and 30 mm wide, supported at either end. It supports a weight-bearing wheel that can roll along the plate. It currently supports the maximum weight ...
17
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6answers
4k 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 ...
16
votes
6answers
11k 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
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2answers
640 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
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5answers
8k 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
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3answers
4k 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?
15
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5answers
7k views

Purpose of spheres and fins on submarine propeller

On a recently launched Russian diesel-electric submarine, the rear propeller has two distinct features. You can see spheres at the base of every propeller blade: Also, the trailing edge of the shaft ...
14
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3answers
7k views

How do bike wheels keep turning when the rider stops pedalling?

I am very confused with something regarding bikes... How is it that a bike wheel continues to spin (either from momentum or from going downhill) when the rider is not pedalling, without also spinning ...
14
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5answers
757 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. ...
14
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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
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3answers
4k 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?
14
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7answers
11k 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 ...
14
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3answers
122k views

Calculation of Clamping force from bolt torque

I'm trying to calculate the clamping force resulting from torquing a nut and bolt to a particular level. I have found this formula in various forms in a lot of places. $$T = KDP$$ $T$ = Torque (in-...
14
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4answers
2k views

In aluminum machining, what are the most common factors that might cause a machined component to have warping issues?

I am currently having an issue where features of my machined parts are warping. I am using Alloy 7050 Type I and Type III in this particular case. Using a feeler gauge and a certified, calibrated ...
13
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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
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3answers
8k 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
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3answers
3k 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
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3answers
9k views

How different are dc motor designs from dc generator designs?

Some dc motors can be used as generators as well by applying mechanical torque to the output shaft to induce a current. However, even if a dc motor can do this, I imagine they were not designed for ...
13
votes
1answer
361 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 ...
13
votes
2answers
234k views

How to calculate flow rate of water through a pipe?

If a water pipe is 15 mm diameter and the water pressure is 3 bar, assuming the pipe is open ended, is it possible to calculate the flow rate or water velocity in the pipe? Most of the calculations I ...
13
votes
3answers
6k views

How to prevent deposition of dust on ceiling fan blades

It is well known that dust gets deposited on a rotating ceiling fan because formation of a boundary layer over fan blades. The air layer next to blade surface is stagnant due to no-slip condition and ...
13
votes
4answers
1k views

Easy nonlinear model for large deformation of a beam

I have a beam subject to twisting and/or bending forces as well as linear compression force along its main axis. It is modelled as an isotropic beam, but if anisotropic is not too far off then that's ...
12
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6answers
6k views

Why does a gear have extra holes?

In a gear you normally have a center hole for the shaft to be put into. Why do some gears have holes surrounding that center hole? Is it for weight reasons? Does it add stability? Is it so you can add ...
12
votes
4answers
4k views

How thick is it reasonable for the walls of a steel gas pipeline to be?

The TurkStream project site claims the gas pipeline will use pipes made from 39 millimeters of high-quality carbon manganese steel with additional plastic coatings on both sides. Yes, they claim 39 ...
12
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5answers
17k views

How to calculate lever force when lever has uniformed distributed load?

We have a simple class 1 lever: $$\begin {array}{c} \text {5,000 kg} \\ \downarrow \, \downarrow \, \downarrow \, \downarrow \, \downarrow \, \downarrow \, \downarrow \, \downarrow \, \downarrow \, \...
12
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3answers
1k views

Thermoelectric Technology to Harvest Energy from Internal Combustions Engines

Background: In an automobile, only 1/3 of the potential energy in the fuel is converted into mechanical energy and significant portion of the energy is lost as heat. There have been previous ...
12
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3answers
6k views

Can a magnetic lock be negated or overcome by a stronger electromagnet?

Magnetic locks seem to be fairly common on the doors of modern buildings, but I question their reliability when compared to a traditional, mechanical lock. I realize that the strength that it would ...
12
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3answers
4k views

Which turbulence models are suitable for CFD analysis on a streamlined vehicle body?

Many commercial and open-source CFD codes implement several closure methods for the non-linear convective acceleration term of the Reynolds-averaged Navier-Stokes (RANS) equations. Common methods (...
12
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5answers
2k views

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 ...
12
votes
1answer
470 views

What causes the sound coming from electrical vehicles?

All the electrical vehicles I've ever ride make that humming sound (either cars or trains). What exactly causes that sound? Is it drag force in the gears? Is it a fan? Or is it because of the coils (...
12
votes
4answers
6k 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 ...
12
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3answers
2k views

Schematic Diagrams for Mechanical Systems

Is there some sort of equivalent standardized schematical (topological) diagram -such as Piping and Instrumentation Diagram, Electrical Schematics, Process Flow Diagrams, etc.- for the realm of ...

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