PDA

View Full Version : When does statics get hard?

cs
09-22-2008, 12:30 PM
So far it is pretty simple and can really be summed up with just a few statements.

To find the forces at a point you sum up the forces in the X direction and you sum up the forces in the Y direction. The resulting force is the triangle created by these X & Y's. If you need the momement it is just Force (perp to point) times the distance away from the point.

The rest is just how you get there and all you have to be able to do is to see triangles and relationships.

I'm sure it will get tougher, but so far that is about it. Most of the folks in class are having a hard time seeing this. My only problem is re-commiting Law of Sines and Cosines back to the memory banks (I purged those out a long time ago).

TimH
09-22-2008, 12:32 PM
It gets hard when you are taking calc3 and physics at the same time and working a full time job on top of it.

P.I. Stazzer-Newt
09-22-2008, 12:34 PM
It gets tougher when you go 3D.
It gets tougher when you have to consider the changes due to deflection.
It gets tougher when you need to consider the stress distribution within a multi-material component.
And if you need to consider stiction in pivots.

cs
09-22-2008, 12:35 PM
Ughh!! Calc 3.

Tylerdurden
09-22-2008, 12:38 PM
I found it gets harder the less you drink between classes.:D

No water bong hits for you.

cs
09-22-2008, 12:38 PM
The thing about all those options you mention is that (the way I see it) is you just have to break the problem down to one force at a time. Deflection might cause a little wrinkle, but the rest appears that you just break it down and solve one part of the problem at a time it should be okay.

This course is not near as complicated as Structures 1 and Structures 2 (concrete and steel design).

P.I. Stazzer-Newt
09-22-2008, 12:44 PM
If the course is well put together and well taught then it shouldn't get hard - the calculations may become tedious but you should know how to break it down into a series of do-able steps.

Katherine
09-22-2008, 12:48 PM
Statics get hard when it becomes dynamics. As soon as things start to move, they go to hell fast.:D

Canoez
09-22-2008, 12:52 PM
Statics get hard when it becomes dynamics. As soon as things start to move, they go to hell fast.:D

Agreed.

And when you have to apply the statics for things like Mechanics of Materials or measuring strain with strain gages. Mohr's Circle is lots of fun!

Keith Wilson
09-22-2008, 01:13 PM
Statics get hard when it becomes dynamics. As soon as things start to move, they go to hell fast.Exactly. Statics doesn't ever get very hard, although 3D is more complicated. Dynamics and deformable body mechanics is harder. Will you take differential equations, or will you stop with calculus? Diffeqs was when it got really nasty for me. Fortunately I've never once had to use the damn things.

cs
09-22-2008, 01:26 PM
This course is titled Statics & Stength of Materials (1&2). Not sure how much into dynamics this course will go. At this level this is where I stop. Not sure what is needed at the BS level.

If I had to go back and take Calculus 2 I would be lost. It has been 100 years since I took Calculus 1.

George Roberts
09-22-2008, 03:43 PM
Non-linear Continuum Mechanics II. Tensors. Inverse problems.

Simple problem - A beam is supported by 3 piers. A general load is placed on the beam. For the general load compute the reaction at each pier. There is no basis to assume that the tops of the piers are in line. But the beam is a single piece of material and is straight when unloaded.

---

The questions asked make the subject hard. You are being given simple questions.

The hard questions are phrased as design questions. They typically are phrased as: Optimize the solution to this problem relative to this cost matrix.

Katherine
09-22-2008, 06:34 PM
I've never once had to use the damn things.Same here.:rolleyes:

hokiefan
09-22-2008, 07:34 PM
Exactly. Statics doesn't ever get very hard, although 3D is more complicated. Dynamics and deformable body mechanics is harder. Will you take differential equations, or will you stop with calculus? Diffeqs was when it got really nasty for me. Fortunately I've never once had to use the damn things.

Same here, in the literal sense. I bet though that you've used them in a conceptual way to get an intuitive understanding of a problem. I have used very little of my technical engineering training, especially as I moved out of Mechanical Engineering into Process Controls, then into operations. But all that stuff shapes your intuition and understand of the world you work in.

And you're right, statics was not hard, just became complicated as things were added. Dynamics was fun at the beginning, that got hard real fast. Vibrations started hard and got worse. I could do the work, but I never really "got" thermo until I was working in the real world, then I wanted to go back and take all three quarters over to really learn it. Ah well, such is life.

Cheers,

Bobby

Keith Wilson
09-22-2008, 07:57 PM
I dunno - calculus certainty; it's elegant, and gives you a good intuitive grasp of things even if you don't work out the math in detail. Diffeqs didn't have any theoretical center; it was a series of tricks for solving certain limited types of equations - and besides, everything I knew about it leaked out of my ears and evaporated as soon as I passed the final.

hokiefan
09-22-2008, 08:10 PM
I dunno - calculus certainty; it's elegant, and gives you a good intuitive grasp of things even if you don't work out the math in detail. Diffeqs didn't have any theoretical center; it was a series of tricks for solving certain limited types of equations - and besides, everything I knew about it leaked out of my ears and evaporated as soon as I passed the final.

Like you, I found calculus easier to "visualize" and use. But I think of "difficult equations" as the basis for a lot of my intuition because they are at the core of describing anything that vibrates, including process controls if you don't get it right. At one point, I was taking a Vibrations, Control Theory, and some sort of Electrical Engineering elective and it dawned on me that they all used the same math. In Control Theory it was called Laplace Transforms, but it was the same imaginery number math to describe the vibration, whether it be mechanical, electrical, or a process. About that time I had the illusion that I actually understood imaginery numbers.:eek: Later realized that I didn't understand them, just knew how to use them. I mean, who can understand what is the square root of -1? Bigger minds than mine maybe.

Cheers,

Boby

carioca1232001
09-22-2008, 08:20 PM
I suspect that the approach to teaching mathematics is what can account for lack of interest in its practical applications.

'Calculus' can be thought of simply as differentiation and integration, as university entrance exams in the UK portray it.

But one has hardly enrolled himself in Part I B.Sc.(Honours) Eng, when the lecturer comes along and introduces simple diff. equations........and relates these to physical processes that are pertinent to all engineers in the Part I core curriculum.

Motivation gains an impetus, although the 'course work' is sordid and motivation wanes...;)

Finally, a graduate engineer finds himself driving a jalopy around bends on a dirt road (no asphalt !)....'where are my shock absorbers ? ', he exclaims :rolleyes: Diff equations come to mind :D

Keith Wilson
09-22-2008, 08:20 PM
The common mathematical descriptions of mechanical spring-mass-damper systems and their hydraulic and electrical analogues were very cool. Yeah, I wish I had worked harder on Laplace transforms. Maybe I would have really understood them - or maybe not. Well, next lifetime.

hokiefan
09-22-2008, 08:35 PM
The common mathematical descriptions of mechanical spring-mass-damper systems and their hydraulic and electrical analogues were very cool. Yeah, I wish I had worked harder on Laplace transforms. Maybe I would have really understood them - or maybe not. Well, next lifetime.

While I never worked with them, the spring-mass-damper system gave me the mental picture I needed to visualize the other types of vibrating systems. And I probably wouldn't have tied the math together as easily if I hadn't taken the three different "vibrations" classes together in the same quarter. Very tough, but rewarding quarter. It is kind of funny, I was pretty good at Laplace transforms, but probably only used them once in the real world. They are built into my control tuning intuition though.

But most ME's wouldn't have taken all three of those classes, just the vibrations one, since that particular Controls class was the 2nd or 3rd quarter. Since I played my first junior year, I had to take an extra year to get things back on track. That gave me room for a number of extra technical classes and somewhere in there I got interested in Controls, typically a ChemE or EE field. Having too much already invested in my ME degree, and grades that probably wouldn't have gotten me into either of those departments :eek:, I finished my ME degree and took as many applicable classes in the other departments as I could.

Cheers,

Bobby

Keith Wilson
09-22-2008, 08:44 PM
I took a course in systems analysis that had all three together, with Laplace transforms. It would have been a great course, except it was taught by one Dr. Ogata, who was probably quite a brilliant fellow, but whose command of English was not up to the task. That wouldn't have been insurmountable, but he had written the textbook too. Whoever edited it had made everything into correct grammatical sentences, but apparently didn't understand the subject well enough to ensure that the sentences all made sense. Either that or I was just too thick-headed to quite grasp it, or maybe some of both. I've never used any of it since. The sort of machines I design, if things start to vibrate, you can always weld on a couple more 1/2" thick stiffeners.

carioca1232001
09-22-2008, 08:52 PM
I took a course in systems analysis that had all three together, with Laplace transforms. It would have been a great course, except it was taught by one Dr. Ogata, who was probably quite a brilliant fellow, but whose command of English was not up to the task. That wouldn't have been insurmountable, but he had written the textbook too. Whoever edited it had made everything into correct grammatical sentences, but apparently didn't understand the subject well enough to ensure that the sentences all made sense. Either that or I was just too thick-headed to quite grasp it, or maybe some of both. I've never used any of it since. The sort of machines I design, if things start to vibrate, you can always weld on a couple more 1/2" thick stiffeners.

That is an awful book, I mean, the one authored by Ogata !

The approach, as I had stressed earlier, makes a heck of a difference.

It´s like having just baled off a landing craft on D-Day, in waist-deep water, with the defenders pouring lead in your direction.....and no way out of the situation ;)

hokiefan
09-22-2008, 09:07 PM
I took a course in systems analysis that had all three together, with Laplace transforms. It would have been a great course, except it was taught by one Dr. Ogata, who was probably quite a brilliant fellow, but whose command of English was not up to the task. That wouldn't have been insurmountable, but he had written the textbook too. Whoever edited it had made everything into correct grammatical sentences, but apparently didn't understand the subject well enough to ensure that the sentences all made sense. Either that or I was just too thick-headed to quite grasp it, or maybe some of both. I've never used any of it since. The sort of machines I design, if things start to vibrate, you can always weld on a couple more 1/2" thick stiffeners.

I had a professor something like that for Thermodynamics, 3rd quarter of a 3 quarter series. Could not explain anything, I mean absolutely nothing. We'd ask a question and got the original explanation in response. The saving grace was he gave easy test, I mean really easy tests. If you didn't figure out how to get an A or a B in his class, you really didn't deserve to graduate.

Was talking with another professor later that I truly respected, and told him I thought this guy was a real idiot. He laughed and told me the guy was a true Thermodynamics research genius. He brought in more research money than the next four professors combined and had done some truly cutting edge research over the years. He was, my professor friend acknowledged, a pretty bad instructor. Problems that took 3 pages of work he did as one step in his head. He truly didn't see what we didn't get. But the rules at the Virginia land-grant universities said every professor had to teach. So they had him teach one session a year of 3rd quarter Thermo, where he did little damage. They had coached him on setting up his tests so he didn't hurt anyone's grades either. Worked for him, because complaining students cut into his lab time. And back to his lab he happily went.

I'm sure I had others, but the only book I remember written by the professor was a good one. It was Mechanisms and Dynamics of Machinery, by HH Mabie & FW Ocvirk. I had Mabie as the professor and he almost apologized for using his own book, but he said he had tried very hard to write a book that made sense. He was a good teacher, with industrial experience, and he did write a good book.

Ah, you're bringing back some good memories now.

Cheers,

Bobby

cs
09-22-2008, 09:25 PM
Okay you guys have moved on into the rocket science and I'm just a simple carpenter. ;)

carioca1232001
09-22-2008, 09:31 PM
Sorry to disappoint you Chad.......but the real rocket scientists......are definitely down to earth types !

hokiefan
09-22-2008, 09:31 PM
Okay you guys have moved on into the rocket science and I'm just a simple carpenter. ;)

Nah, its just everyone takes a different path along the way. Its part of what makes life interesting. Everyone knows more about something than someone else!

Cheers,

Bobby

cs
09-22-2008, 09:33 PM
Well I can at least almost gurantee that I'm the best rocket launcher crew chief here on this forum. :D

hokiefan
09-22-2008, 09:38 PM
Well I can at least almost gurantee that I'm the best rocket launcher crew chief here on this forum. :D

Now if you were talking about model rockets, you know the Estes kind, I'd probably argue. But since you're probably talking about the big kind that make things at the other end of the flight path go "BOOM", I'll bow to your superior knowledge.:D

Cheers,

Bobby

cs
09-22-2008, 09:40 PM
What I should do on the test is give all my answers for direction in mills. Bet that would mess with the teacher's head.

Mrleft8
09-22-2008, 09:59 PM
OK.............. Are we taliking STATISTICS, or STATICS? Cuz I'm getting all kerfuzzled here....

pipefitter
09-22-2008, 10:12 PM
The sort of machines I design, if things start to vibrate, you can always weld on a couple more 1/2" thick stiffeners.

I built a full size tower for an engineer and I had my prototype drawn out on my table full size with some angles to depict oscillatory movement and placement and attitude of trussing. He watched the whole process and yet he was perplexed, drawing the theory of his own on the white board claiming I had overbuilt the structure while adding unnecessary weight and expense. He drew a boat and it's expected forces from wave impact, load height weight deflections at different speeds etc. The look on his face when I informed him that my calculations were those of the foundation of the piece with it's upper third folded forward. . .traveling down the highway in the boat on it's trailer. . .

Vince Brennan
09-22-2008, 11:16 PM
Lefty.... are these guys even talking ENGLISH anymore?

I fell like the Montana trucker who got lost in Canada and stopped to ask where he was...

"Saskatoon, Sascatchewan!" came the reply, whereupon the trucker turned to his co-driver and said, "Jeez, they don't even speak English here!"

(PS: Good luck Thursday!)

cs
10-08-2008, 12:08 PM
I got the results from the first test in Statics today. He had an extra credit problem on the test worth 15 points and my score on the test was 115.

BTW Doug it is Statics - The study of forces when all forces are in equilibrium, once they start moving it is dynamics.

TimH
10-08-2008, 12:09 PM
I may go back for my Masters yet....

Popeye
10-08-2008, 12:14 PM
i seem to have misplaced my pocket protector

cs
10-08-2008, 12:14 PM
What do you mean at my age? I'm just now getting ready to turn 24. :D;)

Keith Wilson
10-08-2008, 12:15 PM
Chad, you do that well in statics and you won't be able to claim you're "just a simple carpenter" anymore. Good job!
That is an awful book, I mean, the one authored by Ogata ! THANK YOU! I'm very glad to have that corroborated; for a while I thought it was just me.

Captain Blight
10-08-2008, 12:18 PM
Not even 24 and 16,418 posts already? That's a whole lot of homework not gettin' done!!

cs
10-08-2008, 01:17 PM
I actually found a problem (really 2 problems) that I might not have been so generous on if I was grading.

On this one problem the sum of the forces in the Y direction totaled 37.5, and I showed that. When I went and wrote the summary of my F(x) & F(y) I wrote 32.5 instead of 37.5 so my resultant force was 73 instead of 75. He gave me credit for that.

The next problem was in what direction from the X axis was the force acting. Being as I had wrote 32.5 instead of 37.5 my angle was off just a hair, but he gave me credit for it.

It helped that I showed all of my work and all of my steps. When I looked back at it was pretty obvous what I did and so he saw my thought process and saw that it was correct, just a transposition error.

cs
10-08-2008, 01:33 PM
Just so you can see the problem here is a scanned portion of the test. The problem was 11 & 12. If I had been grading I would have at least knocked of a point or two, but I wasn't grading so I recieved a perfect score. :D

http://farm4.static.flickr.com/3074/2925113112_6048b32535_b.jpg