#1
I need an online source where I can find an explainantion of beam mechanics.

I'm utterly confused about bending moments. I know about simple torques, but I'm completely confused about stuff like the "bending moment at x".

Thanks.
Quote by neidnarb11890
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#3
If i understand you right...
The moment is the product of the mass and the perpendicular distance from the pivot to the line of action of the force produced by the mass...
Simply, mass x distance = moment
#4
Quote by benrochlin
If i understand you right...
The moment is the product of the mass and the perpendicular distance from the pivot to the line of action of the force produced by the mass...
Simply, mass x distance = moment



Not mass buddy, weight.

M=F*d

It gets a fair ways more complicated when dealing with a beam with multiple pivots, etc. What are you trying to do? I'm a 3rd year ME, I might be able to help.
#5
Do you have your engineering book. This, for me, was in Statics and Mechanics of Materials. If you read those letters that they group together into things called words, you can gain an understanding of these concepts.

But benrochlin pretty much has it. If you have a force on a beam of 10 lbs, say 3 ft from where you are taking the moment (lets say pt. A), then your moment about pt. A is 30 lb*ft. If it's an angled force, you take the perpendicular force to the beam through trig. So say 10 lbs at 45 degrees, your moment about A from previous example would be 10lb*cos(45)*3ft, which is 21.2 lb*ft.

If you need examples of problems worked out, search for a solutions manual for your book online. If you have a R.C. Hibbeler, you can get a cramster account and have all you need. There are worked out examples of pretty much all the problems.
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#7
It's not mass that is multiplied by the distance, it's the force applied perpendicularly to the beam. Sometimes you'll have distributed loads that need a central point. So say like 10 lb/ft over a 5 ft bar, then moment is 50 lb at 2.5 ft from your moment pt. It's 5 ft * 10lb/ft which is 50lb cause ft cancel. Then the mid point is where that 50 lb is applied.
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#8
Quote by hawk5211
Not mass buddy, weight.

M=F*d

It gets a fair ways more complicated when dealing with a beam with multiple pivots, etc. What are you trying to do? I'm a 3rd year ME, I might be able to help.


I'm reading a paper on improving the classical capstan equation, where the rope is modelled as a beam.

I just can't understand stuff like "a pure moment applied at point A on the beam". I thought a moment was just a turning effect of a force.

And the internal bending moment - is that the turning effect of a cross-sectional slice about the neutral axis due to stresses?



Thanks.

(I'm a maths student)
Quote by neidnarb11890
the chinese take-out place my family always ordered from gave you chopsticks, so as a kid it was fun to try & eat with chopsticks
now i just use a fork, 'cuz nothing is fun anymore & i just want to shovel food into my mouth to fill the void
#10
The biggest thing to gaining an understanding of these concepts is abusing yourself and sitting at your desk studying for way too long for too many nights. As far as resources, your text and anything you can get from your professor like practice test that are worked out. It's especially helpful to see how your prof works out stuff so you can see what he expects. Then for finding textbook solutions you can just type in the problem as you see it in the text and you can usually find guides and such through google.
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Roland Cube 30x


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#11
"And the internal bending moment - is that the turning effect of a cross-sectional slice about the neutral axis due to stresses?"

Yes. It can be applied anywhere through out the beam
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Gibson SG '61 Reissue 'Aretha'
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#12
Quote by rhcpjhlz
"And the internal bending moment - is that the turning effect of a cross-sectional slice about the neutral axis due to stresses?"

Yes. It can be applied anywhere through out the beam


This is the thing. When studying I often have the feeling that I do understand it, but I can't find it written down anywhere. Haha.
Quote by neidnarb11890
the chinese take-out place my family always ordered from gave you chopsticks, so as a kid it was fun to try & eat with chopsticks
now i just use a fork, 'cuz nothing is fun anymore & i just want to shovel food into my mouth to fill the void
#13
It made sense in my tired undergrad head... the way i always get the hang of it is by making a couple of assumptions, trying a couple of things, and seeing if everything still works. cw and acw moments balancing is a good way to check (if the system is in an equilibrium state)
Best thing will always be practice on progressively harder example questions if you can find any.
#14
Quote by rhcpjhlz
Do you have your engineering book. This, for me, was in Statics and Mechanics of Materials. If you read those letters that they group together into things called words, you can gain an understanding of these concepts.

But benrochlin pretty much has it. If you have a force on a beam of 10 lbs, say 3 ft from where you are taking the moment (lets say pt. A), then your moment about pt. A is 30 lb*ft. If it's an angled force, you take the perpendicular force to the beam through trig. So say 10 lbs at 45 degrees, your moment about A from previous example would be 10lb*cos(45)*3ft, which is 21.2 lb*ft.

If you need examples of problems worked out, search for a solutions manual for your book online. If you have a R.C. Hibbeler, you can get a cramster account and have all you need. There are worked out examples of pretty much all the problems.


Hmmm. Interesting.

I'm just randomly looking through this for fun.
#15
tourques are twists, bending moments are caused by forces on something that could be allowed to bend,

the farther X is from the force, the greater the bending moment, as bendings moments have hte unit Nm

Since it sounds like you are just starting statics, bending moments will likely just be calculated by force*distance. As anything with barriers preventing a bend at a specific position require derivate calculations to determine the bending moment at a specific position on the part being analyzed
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