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A Journal of Applied Mechanics and Mathematics by DrD

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Why You Shouuld NOT Use the D'Alembert's Principle

Mechanics Corner   #50 A Journal of Applied Mechanics and Mathematics by DrD                                    Why You Should NOT Use the D'Alembert's Principle I think it is safe to say that every engineering student studies both Statics and Dynamics. We are told that Statics is easier than Dynamics, which is often true but not so in all cases. When we get to Dynamics, many teachers, particularly physics teachers, will urge the use of something called D'Alembert's Principle. The
DrD

DrD

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Where Would You Publish It?

Mechanics Corner Where Would You Publish It? Since long before my time, there has been a desire to have important results published where they become accessible to many others. Some of the great names, such as Newton, Euler, Bernoulli, and others, we know primarily because of what they published. Their work formed the fundamentals upon which modern engineering and science is built. Publication of research results has long been particularly important to faculty members; it is often take
DrD

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Where Will I Find A Job??

Where Will I Find A Job?? As I read over the questions that readers post here on ME Forum and elsewhere, I sense a common theme in many of them. There seems to be a wide, dare I say almost universal, concern about where those currently in college will find employment after graduation. To a degree this is entirely understandable; we all wonder what is in our future. Even so, the level of anxiety that I sense in many of your postings strikes me as extraordinarily high. Let us consider this a bit.
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DrD

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Where is this?

Does anyone recognize where this video is shot? Is it a group of students at a school (what school?), or is it an industrial site (what company)? I am anxious for someone to locate this for me, please. DrD   Saurabh Jain, our host, has identified this location for me, and that is much appreciated. When I watched the video, I was aghast at all those nearly bare feet in a machine shop! I can appreciate that in Indian culture, the simple sandals are socially quite acceptable, bu
DrD

DrD

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When You Ask for Help ....

Today, I have a question for readers. I'd like to get everyone who is willing to answer the same question, but also tell me whether you are a practicing graduate engineer or if you currently a student. I think these two groups will answer somewhat differently, so it is important that you identify which one you fall into. The question is really simple: When you ask for help, what do you really want? Are you asking for someone to step in and solve a problem for you? Or, are you asking for a f
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Mechanics Problem

Wheel Climbing A Step

Mechanics Corner     A Journal of Applied Mechanics and Mathematics by DrD, # 55     © December, 2020                                                        Wheel Climbing A Step Introduction     The problem that follows was brought to my attention by a student at a great European university. It was a part of a much bigger problem with which the student was engaged, but this is quite enough to hold our interest. The results are differential equations of motion which could
DrD

DrD in Mechanics Problem

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What/Where to Study -- Another Opinion Piece

What/Where to Study Introduction I do not have the definite statistics available, but it appears to me that the majority of the readership of ME Forums is made up of students, with a much smaller number of readers at other points in their careers. By far the greatest part of these students appear to be in India, with a number in Southeast Asia and the Middle East; there are of course a few folks scattered all over the globe. It has been very interesting to me to learn about all of you, to gain a
DrD

DrD

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What Would You Like to Know?

What Would You Like  to Know? If you could ask me any question you want, what would you like to know that you think I might know? I certainly do not know everything, but through the years I have accumulated a certan amount of knowledge that I'd like to pass on to you. Therefore, I ask, what would you like to know? Many readers are still in college, and no doubt they would like to know what is going to be on the next exam. I'm sorry, but I have no way to know that. What I might be able
DrD

DrD

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What Makes A Ship Move?

Mechanics Corner A Journal of Applied Mechanics and Mathematics by DrD, #47                                                               What Makes a Ship Move? One of the problems that often confronts engineers is the description of large, interconnected systems. Engineers tend to specialize, so that one is very knowledgeable on gears, another knows bearings, a third knows pumps, but none of them are comfortable with the whole system. In the automotive context, this is often exp
DrD

DrD

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War Stories

Mechanics Corner     A Journal of Applied Mechanics and Mathematics by DrD     © Machinery Dynamics Research, 2016 War Stories -- Dr. Jack Levedahl Today I want to tell a few war stories, war stories in the literal sense of the word, in that they all relate in one way or another to World War II. They all center on my friend Dr. Jack Levedahl, a most excellent mechanical engineer and adventurer. Jack was an elderly man when I first met him about 15 years ago, and he has since passe
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DrD

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Verbal Description of a Doonesbury Cartoon

The following is a verbal description of a Doonesbury cartoon of unknown date by Garry Trudeau. Doonesbury has long been one of America’s major cartoon strips, with a very dry wit and a decidedly left-of-center outlook. I found this today in going through some old files. SCENE: A college classroom, the teacher lecturing in a rather absent minded fashion, the students silently bent over, taking notes and keeping their heads down. TEACHER: Of course, in his deliberations on American capitali
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Value Engineering

A toothpaste factory had a problem.  They sometimes shipped empty boxes, boxes without the tube inside. This challenged their perceived quality with the buyers and distributors. Understanding how important the relationship with them was, the CEO of the company assembled his top people. They decided to hire an external engineering company to solve their empty boxes problem. The project followed the usual process: budget and project sponsor allocated, RFP, and third-parties selected.  Six months (
DrD

DrD

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Two Short Math Problems

Mechanics Corner A Journal of Applied Mechanics and Mathematics by DrD, #40 July, 2017   Two Short Math Problems Do you ever read the ads that appear on ME Forum? I try to avoid them as much as possible, but an organization called BRILLIANT has put up some interesting math problems of late that have caught my eye. Two of them are the subject of today's post. The first problem that I want to discuss is actually more recent than the other, but it gives us a good plac
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DrD

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Two Balls Rolling On An Incline

Mechanics Corner     A Journal of Applied Mechanics and Mathematics by DrD, # 37     29 April 2017 Two Balls Rolling On An Incline A Problem Where I Learned Something New Introduction     In previous articles, I have mentioned another web site called Physics Forums (PF) where people post problems for which they need help. In this note, I want to present to you one such problem and it solution, along with a new insight that came from another commenter at PF, one of the advi
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Twenty One Rules for Tech Writing

Twenty One Rules for Tech Writing Introduction One of the things that has surprised me about the readers of ME Forum is the number of folk who want to publish technical papers. When I was an undergraduate (a very, very long time ago), publishing papers was the farthest thing from my mind. I knew that publishing was a concern for some of the faculty, but it was certainly no concern of mine! To my even greater amazement, most of those desiring to write want to write in English, even though this is
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DrD

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Triple Rocker

Mechanics Corner A Journal of Applied Mechanics and Mathematics by DrD July 31, 2017 Triple Rocker Over at the Kinematics of Machines club, I recently ask if anyone could show me an example of a four-bar linkage that would be classed as a triple rocker. In the terminology of four-bar linkages, a link is classed as either a crank or a rocker: Crank - can rotate in a complete circle Rocker - cannot rotate in a complete circle] Thus my question was for an example
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DrD

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Torsional Stiffness of a Shaft -- Part I -- #22

Mechanics Corner  A Journal of Applied Mechanics and Mathematics by DrD, # 22 (c)  Machinery Dynamics Research, 2016 Torsional Stiffness of a Shaft -- Part I          Introduction          A shaft is a common machine element, used to transmit rotational motion and torque from one component to the next. It is clear that the length of the shaft must be sufficient to span the distance from the first component to the second, but what should the diameter be? The answer to this quest
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Torsional Stiffness of a Shaft - Part III -- #24

Mechanics Corner     A Journal of Applied Mechanics and Mathematics by DrD, # 24     © Machinery Dynamics Research, 2016 Torsional Stiffness of a Shaft -- Part III         Introduction     The discussion in previous parts of this series has focused on stiffness (or compliance) estimates for various shaft geometries. There has been nothing said yet about joining parts together, although most readers will readily agree that integral (single piece) shaft assemblies are very rare
DrD

DrD

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Torsional Stiffness of a Shaft - Part II -- #23

Mechanics Corner     A Journal of Applied Mechanics and Mathematics by DrD, # 23     © Machinery Dynamics Research, 2016 Torsional Stiffness of a Shaft -- Part II          Introduction          In the previous post of this series, a variety of shaft forms involving both solid and hollow sections were considered. A general approach was developed, applicable to various sorts of non-uniform shafts, but always subject to the provision that the variation in section was gradual; n
DrD

DrD

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The VEProject --- Shifted Levers --- A Critical Assessment

The VEProject --- Shifted Levers A Critical Assessment      Introduction     The subject of this article is the VEProject Shifted Lever video, as found at the following URL:   https://www.youtube.com/watch?v=8TniRMwL2Vg     The video shows a "Shifted Lever" mechanism, a device that appears to be perpetually off balance. It is presented as a perpetual motion mechanism, that is, a machine that will run forever without any energy input other than, perhaps, an initial push. This presentation comes
DrD

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Suddenly Lifted Bar - Revised

The previous post on this topic was certainly acceptable for engineering purposes, but there was one small oversight in the model. Many would actually prefer that oversight because it makes the algebra quite a  bit less complex. Even so, it is not quite correct, so this revised post is offered to correct the oversight. There are also a few additional comments that may be of interest, and a final question for the readers to consider. DrD LiftedBar_Revised.pdf
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Suddenly Lifted Bar

Mechanics Corner     A Journal of Applied Mechanics and Mathematics by DrD, # 51     © 4 July, 2020   Suddenly Lifted Bar Introduction     In the Forum section, under the Machine Dynamics and Design Considerations heading, Mr. Negar Rahbar has posted a topic, Bending Moment. It is a problem he found in an older textbook (one that I might have studied back in my college days, although in this case, I did not), a book titled Theory and Problems of Machine Design by Allen
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Engineeering Stories

SR-71

I've seen this plane close enough to touch it. It is the most frightening machine you can imagine. DrD   SR-71 Blackbird: The Cold War's ultimate spy plane     (Image credit: Lockheed Martin) By Stephen Dowling1st July 2013   Colonel Rich Graham spent 15 years as a Blackbird pilot and wing commander. He told BBC
DrD

DrD in Engineeering Stories

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Something Light -- A few jokes

1. Team building is very popular in industry these days, so here is a team building joke. A group of mathematicians are attending a weekend seminar on team building. During the night, a fire breaks out in the room of one of the mathematicians. He quickly tears pages out of his notes and lights them on fire, one by one. He then runs down the hall, shoving burning sheets of paper under the doors of all the other mathematicians. In the morning, after the building is burnt to the ground, the fire ma
DrD

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Rocket Homework Problem

Mechanics Corner     A Journal of Applied Mechanics and Mathematics by DrD, #38       Machinery Dynamics Research, 2017 Rocket Homework Problem Introduction     Most engineers find problems involving rockets to be exciting. There is something about a rocket that fires our imagination, whether we think of going to the moon or one of the planets, or simply of shooting down an incoming missile. The subject of this post involves a rocket on a mobile launcher. The rocket is i
DrD

DrD

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