Engineering/Physics Question

mbalbritton

mbalbritton

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Mar 22, 2005
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Lakeland, FL
Would one of these prove to be more stable than the other?

For sake of easy understanding, think of these as IV stands. Long pole mounted to base with casters. This would be side view.

Explain:
 

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Choice 2. Lower COG and heavier if made of the same material.

Difference is small though. Is this something you need to know for practical use or for class?
 
If lateral forces are placed upon the "pole" the one on the right would transmit those forces down the pole, to the inclined vertical whcih would cause the entire structure to roll. The one on the right it would trasmit down and straight out and over the edge creating a roll metric.

All in all lower center of gravity, more stable
 
They are geometrically the same from a resultant force standpoint. The one on the right should be a little stiffer due to the bends, and more stable because of the lower center of gravity. Thicker material leads to less difference in the stiffness, thinner material leads to less difference in COG.

Also, the added length of the pole on the example on the right would allow it to bend easier.
 
How much lower is the COG if the total height is still the same... As in the pole on the right is ovbiously a little longer than the one on the left?

Man, I dont miss school...
 
I just gotta say...is the chick swinging on it gonna be 105#, or 250#??

Depending on what goes up top...miniscule difference in COG won't matter. Incomplete information to make an informed decision... Had one prof...100 years ago...his answer to a question like that was always "how long is a string?".
 
I am no engineer, so my thoughts on this are uneducated. But my inclination would be the one on the right. My reason would be that with the extended pole going below the caster. It increases the amount of rotation needed to reach the break over point to where it would be tippy.

then I think about a Z-bar draglink. It doesn't matter how you get from the pitman arm to the knuckle the Moment arm is still the same.

With regards to SkyHiK5's answer what if you replaced casters with rubber feet?
 
jeepinmatt said:
They are geometrically the same from a resultant force standpoint. The one on the right should be a little stiffer due to the bends, and more stable because of the lower center of gravity. Thicker material leads to less difference in the stiffness, thinner material leads to less difference in COG.
Also, the added length of the pole on the example on the right would allow it to bend easier.
Click to expand...

x2
 
mbalbritton said:
I am no engineer, so my thoughts on this are uneducated. But my inclination would be the one on the right. My reason would be that with the extended pole going below the caster. It increases the amount of rotation needed to reach the break over point to where it would be tippy.

then I think about a Z-bar draglink. It doesn't matter how you get from the pitman arm to the knuckle the Moment arm is still the same.

With regards to SkyHiK5's answer what if you replaced casters with rubber feet?
Click to expand...

The only thing that would make the right one more stable than the left one is having a lower center of gravity. With any sort of weight placed up high on the pole, this change in COG between styles would be essentially negligible, unless the base had considerable mass.

As far as tipping over, if a horizontal force was applied to the pole somewhere high up, it doesnt matter at all how the pole is attached to the base(assuming the change in COG i mentioned in the last paragraph is small enough to be negligible). The tipping force would be the same.

But it is true, if you are talking very very minute differences, then the one on the right would be more stable.
 
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