Questions tagged [applied-mechanics]

Questions about using applied mechanics to model engineering problems.

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14
votes
3answers
129k 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-...
13
votes
1answer
4k 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 ...
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 ...
11
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5answers
3k views

Practical setup to measure angular velocity

I have got a spinning top from a Canadian manufacturer, and I am deeply amazed by how neatly it spins. My interest in physics has led me to try to find out at what top speed I can spin the top and ...
11
votes
2answers
5k views

Why are tremors of an earthquake felt more on upper floors?

Why are tremors of an earthquake felt most on the upper floors of a building in comparison to lower floors? Does this have something to do with a third class lever?
10
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3answers
14k views

What is the difference between the Polar Moment of Inertia, $ I_P $ and the torsional constant, $ J_T $ of a cross section?

This question is so fundamentally basic that I am almost embarrassed to ask but it came up at work the other day and and nearly no one in the office could give me a good answer. I was calculating the ...
10
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2answers
4k views

Why do we neglect the radial stress in case of a thin pressure vessel?

A cylindrical or a spherical pressure vessel, having inner diameter $d$ & thickness of wall $t$, is called thin if $\large \frac{t}{d}<\frac{1}{20}$. $\bullet$ Thin cylindrical pressure ...
9
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1answer
2k views

"u" vs "n" orientation of channel profiles: why difference in strength?

For example, metal tape measures can be extended and stay straight when in a "u" orientation, but collapse the other way round. I presume the same phenomenon is why metal shelving has sheet metal on ...
8
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4answers
5k views

Why does "potential energy" have the word "potential" in it?

Imagine a block of mass $m$ placed on the ground. I slowly lift it up to height $h$. The work done by me on the block is $mgh$. This amount of energy is now stored in the block when it is at height $h$...
8
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1answer
2k views

Dynamics Simple Pulley System - Stuck on the Process

Have spent hours poring over this homework question but am having difficulty getting the right process going to solve the problem. I don't really know where to start, and I'd really be grateful if ...
7
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2answers
2k views

How do suction cups work?

These are suction-mounting hooks. I want to visualize and understand how do they stick on walls. After these hooks stick on wall. Like we compressed them. How? Since gases are compressible up to a ...
7
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5answers
2k views

Would a centrifugal flyweight governor system slow down the descent of an object that is free falling down to the Earth's surface? (Revised design) [closed]

I am wondering if rotating flyweights would slow down the descent of a object that is free falling down to the Earth's surface. Please reference the conceptual drawing below: This drawing is showing ...
7
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4answers
323 views

Is radians a dimensionless quantity?

Quite often while calculating angular velocity we come across the quantity radians per second. How do I treat radian dimensionally?
7
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5answers
7k views

How can I improve traction on a wheeled vehicle yet reduce friction?

This is inspired by a project I undertook for my Physics class last year; I'd like to apply it in the future. Background: For the project, I and a few classmates were required to build a small car ...
7
votes
2answers
124 views

Adding a lubricant to an already lubricious material, how is CoF affected?

I have a dry film moly-graphite lubricant (CoF=.075) and a lubricious CVD coating (CoF=.05). The CoF of each of these lubricious materials was determined using the same ASME standardized test. The ...
7
votes
3answers
1k views

Compound gear system ratio

This might be a stupid question, but I'm new to mechanics, so please bear with me. Suppose I have a compound gearing system defined in the image below (not to scale). The green gear is the driving ...
7
votes
1answer
3k views

Calculate effort to raise hinged lever with distributed load

My father-in-law would like to install a hinged stair system in his garage that allows him comfortable access to his attic space. He wants the stairs to swing up flush with the ceiling when not in ...
7
votes
1answer
3k views

Principle of Virtual Work vs Castigliano's (Second) Theorem

I had a look online and into some literature however I did not seem to find a good comparison for the two different methods. They are both used for determining displacements and slopes (rotation by ...
7
votes
2answers
2k views

Writing a filtered derivative term of the PID controller into the C++ code

Everywhere I look, be it a PID, lead, lag control or anything else, there are Simulink schematics with transfer functions. This is all nice for system response simulation, however currently I have to ...
6
votes
5answers
8k views

Why are spur gear ratios not always whole numbers in practice?

Defined the Gear Ratio ($i$) as the ratio between the number of teeth on the pinion (driving gear) ($N_{1}$) and the number of teeth on the gear (driven gear) ($N_{2}$). Why is this better, if ...
6
votes
1answer
459 views

Do outer fillets|chamfers also reduce stress as inner ones do?

I kind of have an intuition or at least imagination about how fillet|chamfer of inner edges|vertexes reduce stress (concentration). But does that apply to outer edges|vertexes aswell? Maybe to a ...
6
votes
3answers
1k views

Mounting and Coupling an Encoder

I was wondering how to mount a small rotary encoder to a platform in order to measure how far a small treaded robot has traveled. We're using this tread/wheel set: We've tried epoxying the encoder ...
6
votes
2answers
173 views

Force Balance Question

Hello, I've been asked to show that: $$d\Gamma=\tau 2\pi r^2 dr$$ Where $\Gamma$ is the torque applied to the shaft and $\tau$ is the shear stress of the sample fluid at radius $dr$. So, I know that $...
6
votes
2answers
20k views

How can I calculate the force required to bend a 10 mm thick plate in a rolling machine?

We have a rolling machine with 3 rollers; the bottom has two rollers with diameters of 168 mm and one top roller with a diameter of 219 mm. I want to calculate the required force to bend a 10 mm ...
6
votes
2answers
8k views

Finding the pull-through capacity of a nutted bolt and washer in ASA plastic

I have a uniform load applied to the underside of a plastic sheet which is to be resisted by the combination of a bolt, washer, and nut as depicted below (the other end of the bolt is secured and will ...
5
votes
2answers
11k views

Calculating torque needed to climb a graded hill

I've been designing an electric skateboard which is driven by only one of the rear wheels (for the moment). As I was picking out motors for the board, I soon realized I would need to find a balance ...
5
votes
1answer
357 views

Contradictory units for moments of inertia

I'm looking at a motor datasheet where the moment of inertia is specified in units of "oz in sec^2". I would think that inertia should have dimensions of mass * length^2. I did some further Googling ...
5
votes
4answers
1k views

Plastic modulus

Are there some general guidelines for approximating the plastic modulus of steel under tension so that a bilinear stress strain curve can be defined for Loading beyond the elastic region?
5
votes
2answers
153 views

Longitudinal impact of steel rod on a steel plate to verify the contact duration

So I'm doing an experiment to verify the contact duration when a steel rod (Material: Mild Steel) is allowed to free fall longitudinally on a steel plate. The arrangement is real simple: The rod is ...
5
votes
1answer
157 views

Poisson ratio boundary condition

Let's say I have a large isotropic body in uniaxial tension, onto which a small rectangular piece of film is applied. Think of a strain gage on a big body, but the 'strain gage' is one single ...
5
votes
1answer
582 views

How to transfer rotational energy into lateral energy only when rotating one way?

Is there a general way to convert rotational energy from a gear or something into lateral motion toward or away from the gear? I could use a piston type construction, but I only want the lateral ...
5
votes
1answer
415 views

Axial deformation of variable cross-section member

I've been given a problem which I've attempted to solve, and hope some fellow engineers could possibly see if my approach is correct. We are asked to calculate a column's axial deformation due to an ...
5
votes
1answer
212 views

Minimising permeation rate of hydraulic fluid through hydraulic hose

I am designing an experiment where the hydraulic hose is going to be subjected to relatively high internal pressure for prolonged period of time and it is absolutely imperative that the rate of ...
4
votes
2answers
8k 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 ...
4
votes
4answers
871 views

Is it possible to design a bus that doesn't rock?

Trivially you can prevent rocking with many vehicle by eliminating the suspension. But is it possible to allow a floaty suspension that glides over potholes, without also having to rock back and forth,...
4
votes
2answers
7k views

Increasing Yield Strength with Plastic Deformation

I'm trying to tackle a mechanics problem to be solved using a finite-element analysis, but I'm stuck on one particular bit of theory first. I've done analysis using a linear-eleastic model, and ...
4
votes
1answer
831 views

Why is the Stress vs strain diagram preferable to the Load vs displacement diagram?

I’m really unsure what is the difference between stress vs. strain and load vs displacement graphs and why stress-strain is better. I know that the units are different: stress is in MPa and the load ...
4
votes
3answers
10k views

Are the points of inflection and contraflexure the same?

In theory of bending of beams, often these terms are used. There are no clear definition present. Most of them contradicting. Which of the property(bending moment and shear force) is zero in which ...
4
votes
1answer
2k views

How to Calculate the Minimum Radius a Rod Can Can Be Bent Staying in the Elastic Range?

I am wondering if there is a formula (or how to derive one) for calculating the minimum radius a rod (with a given radius/diameter) can be bent around while staying in the elastic range. Obviously, ...
4
votes
1answer
2k views

A way to calculate the magnitude of the moment

In my engineering textbook, I didnt understand the example given to explain the magnitude of the moment. It asks to calculate the magnitude of the moment about the base point O of the 600-N force in ...
4
votes
1answer
434 views

Biaxial Bending Sign convention

I did a couple of quick calcs to better understand the phenomenon of biaxial bending. One thing that is currently tripping me up is the sign convention. For example, if we have a rectangular beam as ...
4
votes
3answers
128 views

Finding downward force of lever bar

I am working on a DIY project, I am trying to replicate a bar compressor which for some reason is only sold in Europe so I thought it would be fun to make my own without having to waste so much ...
4
votes
1answer
513 views

Optimising driving speed of stepper motor for maximum acceleration by trial and error

I'm writing code for a microcontroller that will ramp up the speed of a stepper motor as quickly as possible, for a jig that I'm building, that moves a workpiece from one position to another along a ...
4
votes
3answers
2k views

What kind of spring exerts a constant force but is also adjustable?

I'm trying to make a lifting mechanism that will support variable weights, similar to this product: http://www.humanscale.com/products/product.cfm?group=quickstand On the quickstand there is a screw ...
4
votes
1answer
85 views

Determine the aceleration of points B,C and D, angular aceleration of rod and the tension in rope DE when ropes AB suddenly breaks

The solutions are F(DE)=134.38N, a(D)=2.016m/s^2 , α=1.29rad/s^2, a(C)=7.828m/s^2 I agree that the FBD and the KD are these: Then to solve this problem I've done: $$\sum M_{c}= I \alpha_{BCD}$$ $<=...
4
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0answers
40 views

What is the purpose of the ink delivery disks found in most rollerball pens

See picture. In most rollerball pens there are those peculiar looking disks near the nib, the purpose of which I have not yet figured out, apart from being some kind of ink reservoir/flow control. ...
4
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0answers
75 views

Calculating the bending moment ($M$) of a beam as it relates to stress ($σ$) and strain ($ε$)?

I am trying to learn how to work out the bending moment for progressively complex systems to model a beam. I am assuming only one axis of motion (transverse = $y$). For the basic equations of motion, $...
4
votes
0answers
73 views

Equation for the spring constant of an orthotropic, rectangular wire spring

I hope I can get some help with this problem as I've been struggling with it for a long time. I have a helical tension spring with radius $R$ and a square wire cross section and made of orthotropic ...
3
votes
3answers
4k views

Moments of Fixed-Fixed Beam

I have a quick question related to the topic of mechanics of materials. If I were to have a beam that is fixed at both ends and has a central point force, do moments develop at the fixed supports? e....
3
votes
2answers
312 views

Spring - Piston with different extension and compression rate

I am in need of a device that extends freely without much resistance but compresses slowly. I can provide a door closer analogy.The door should open fast but close slowly.... Do you think this can be ...

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