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Anonymous Poster #1

center of gravity for L shaped objects

08/30/2013 2:04 AM
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fixitorelse
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#1

Re: center of gravity for L shaped objects

08/30/2013 2:31 AM

If the materials are know you can go to the various manuals that give the weight per foot and figure this out in a short few minutes. Giving me a drawing with nothing to go on is useless.
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Anonymous Poster #1
#2

Re: center of gravity for L shaped objects

08/30/2013 3:21 AM

is there any formula to calculate cg in L shaped objects
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Tornado
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#3
In reply to #2

Re: center of gravity for L shaped objects

08/30/2013 3:50 AM

x-bar = Σi=1n xi wi / Σi=1n wi

Similarly for y-bar.

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PWSlack
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#4
In reply to #2

Re: center of gravity for L shaped objects

08/30/2013 3:53 AM

Just a moment....

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Tornado
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#5
In reply to #4

Re: center of gravity for L shaped objects

08/30/2013 4:43 AM

Well, actually, 2n moments....

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ADIBA NASIR
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#6

Re: center of gravity for L shaped objects

08/30/2013 5:29 AM

Problem:

A uniform carpenter's square has the shape of an L, as shown in the figure. Locate the center of mass relative to the origin of the coordinate system.

  • Solution: We can think of the system as being made up of two subsystems, as shown in the figure. The CM of the left subsystem lies at xCM = 2 cm, yCM = 9 cm. The CM of the right subsystem lies at xCM = 8 cm, yCM = 2 cm. If the mass of a 1 cm by 1 cm square is 1 unit, then the mass of the left subsystem is 72 units and the mass of the right subsystem is 32 units. We find the CM of the system by treating each subsystem as a separate particle, with all its mass concentrated at its center of mass. Then we have for the whole system xCM = (72 units * 2 cm + 32 units * 8 cm)/(104 units) = 3.85 cm, yCM = (72 units* 9cm + 32 units * 2 cm)/(104 units) = 6.85 cm. The CM of the system lies outside of the system. For irregular-shaped objects it is quite common for the CM to lie outside the system. This special point outside the system responds to external forces as if the total mass of the system were concentrated there.
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ADIBA NASIR
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#7

Re: center of gravity for L shaped objects

08/30/2013 5:29 AM
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dineshjegdeesh
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#8
In reply to #7

Re: center of gravity for L shaped objects

08/30/2013 5:36 AM

thanx.............

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#9

Re: center of gravity for L shaped objects

08/30/2013 6:01 AM

Of course, we don't yet have dimensions and weights; but for a wild guess I'll place the CG at 100mm left of the left fillet weld near the middle of the horizontal beam.

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ADIBA NASIR
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#10

Re: center of gravity for L shaped objects

08/30/2013 6:07 AM

But when we have shape with us physically, dimensions are not a big issue and can be measured.

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PWSlack
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#11

Re: center of gravity for L shaped objects

08/30/2013 7:43 AM

There's no dimensions on that sketch. This computer introduces distortion on the vertical relative to the horizontal when presenting on a screen, so how to work it out is anyone's WAG [wild-arsed guess) at this time.

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Fredski
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#12

Re: center of gravity for L shaped objects

08/30/2013 7:44 AM

poorly worded homework question
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K_Fry
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#13

Re: center of gravity for L shaped objects

08/30/2013 2:34 PM

You've shown two dimensions of (what is no doubt) a three dimensional object. Obviously, that three-dimensional object might (and probably) has a various third dimensions, just as there are not single height or width dimensions that fully describe the object.

If you are very lucky, then this drawing represents a two dimensional object. Then the center of gravity (also called the center of mass) of the object becomes meaningless, because the object has no mass.

CAD programs are good a calculating the CG of three dimensional oddly-shaped objects. Without aid of CAD, then the traditional method of summing the moments of each piece of the weldment from an arbitrary point (or a specified point) must be used. This is fairly easily accomplished in a spreadsheet, but it can take a lot of time, nevertheless, particularly to locate the CG in three dimensions.

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ADIBA NASIR (3); Anonymous Poster (1); dineshjegdeesh (1); fixitorelse (1); Fredski (1); K_Fry (1); PWSlack (2); Tornado (3)

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