Shoutbox

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Originally posted by CookieRevised
Easier or harder is irrelevant. The thing would still be in the exact same state. The center of gravity has got nothing todo in all of this.

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So if we would double the weight at the left (and only effecting the center of the gravity) it wouldn't change anything?

I'm still not sure if you are serious or are just trying to troll us with your Zeno style logic...

You are right though...:

if  (cos A)*(mass of chain above BC) > (cos G)*(mass of chain above AC), it will fall to the left.
if (cos A)*(mass of chain above BC) < (cos G)*(mass of chain above AC), to the right.

lets assume the mass of the chain is equal to the distance...
cos A = CD / BC  -> CD = cos A * BC
cos G = CD / AC -> CD = cos G * AC
-->
cos A * BC = cos G * AC
so it will balance...

The way you came to your conclusion just seems wrong

quote:

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Originally posted by CookieRevised
Of course it is not 10Kg pulling on either side, but it IS evenly distributed. Hence there is no extra force pulling more on one side than it is on the other! That is basic (vector) math.

x     y
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  #20Kg

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No, because you are you are adding additional forces in different directions that aren't there in the original system. For example, the horizontal and vertical forces exerted by that chain create two new component forces acting down and towards the centre(which would acts against the slopes).

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Originally posted by CookieRevised
The _all_ math exactly the criteria...

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No they don't. The first 3 of your diagrams contain two slopes at the same angle as each other, Sam's criteria is that one be "flatter" (at a smaller angle to the horizontal) than a "steeper" slope (at a greater angle to the horizontal). Maybe *you* should look at it again.

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Originally posted by foaly

quote:

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Originally posted by CookieRevised
Easier or harder is irrelevant. The thing would still be in the exact same state. The center of gravity has got nothing todo in all of this.

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So if we would double the weight at the left (and only effecting the center of the gravity) it wouldn't change anything?

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Do not take my words out of context. Of course it would change if you would add a force only to one side. But you do not put an extra weight on JUST the left side, you also do the exact same thing on the right!!!!!!!

Or: how is connecting a chain to both sides going to pull on one side harder than on the other?? That is completely impossible, the chain will pull on both sides equally hard (which is what I've said 1243123 times before, but blah)

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Originally posted by foaly
I'm still not sure if you are serious or are just trying to troll us with your Zeno style logic...

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dead serious...

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Originally posted by CookieRevised

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Originally posted by foaly

quote:

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Originally posted by CookieRevised
Easier or harder is irrelevant. The thing would still be in the exact same state. The center of gravity has got nothing todo in all of this.

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So if we would double the weight at the left (and only effecting the center of the gravity) it wouldn't change anything?

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Do not take my words out of context. Of course it would change if you would add a force only to one side. But you do not put an extra weight on JUST the left side, you also do the exact same thing on the right!!!!!!!

Or: how is connecting a chain to both sides going to pull on one side harder than on the other?? That is completely impossible, the chain will pull on both sides equally hard (which is what I've said 1243123 times before, but blah)

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see the edit of my last post

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Originally posted by vaccination
No, because you are you are adding additional forces in different directions that aren't there in the original system.

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Forces which cancel eachother out!!!!!!!!

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Originally posted by vaccination
For example, the horizontal and vertical forces exerted by that chain create two new component forces acting down and towards the centre(which would acts against the slopes).

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You just proved my point....
"acting down and towards the centre"...

aka: they cancel eachother out as they are in opposite direction and there is only a downward net force going from the center of mass strait down. Any extra force going strait down on the center of mass does not have any influence on the movement of that mass, in any system, frictionless, vacuum, whatever. And since the center of mass has therefore NOT moved an inch in the horizontal plane, not a tiny tiny fraction, it is still exactly above the same point as it was before and therefore that extra chain has got NO influence at all on the movement of the top chain.

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Originally posted by vaccination

quote:

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Originally posted by CookieRevised
They _all_ math exactly the criteria...

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No they don't. The first 3 of your diagrams contain two slopes at the same angle as each other, Sam's criteria is that one be "flatter" (at a smaller angle to the horizontal) than a "steeper" slope (at a greater angle to the horizontal). Maybe *you* should look at it again.

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Sorry, but ever heared of limits and delta values?

State what you want, the picture shows exactly what the limits of the system are and is according every criteria SonicSam's teacher has given.

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Originally posted by CookieRevised

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Originally posted by vaccination

quote:

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Originally posted by CookieRevised
They _all_ math exactly the criteria...

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No they don't. The first 3 of your diagrams contain two slopes at the same angle as each other, Sam's criteria is that one be "flatter" (at a smaller angle to the horizontal) than a "steeper" slope (at a greater angle to the horizontal). Maybe *you* should look at it again.

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Sorry, but every heared of limits and delta values?

State what you want, the picture shows exactly what the limits of the system are and is according every criteria SonicSam has given.

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delta != the same

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Originally posted by CookieRevised
aka: they cancel eachother out as they are in opposite direction and there is only a downward net force going from the center of mass strait down. Any extra force going strait down on the center of mass does not have any influence on the movement of that mass, in any system, frictionless, vacuum, whatever. And since the center of mass has therefore NOT moved an inch in the horizontal plane, not a tiny tiny fraction, it is still exactly above the same point as it was before and therefore that extra chain has got NO influence at all on the movement of the top chain.

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Okay now I see what you're saying, but the forces wouldn't be the same either side, surely?

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Originally posted by CookieRevised
Both the ends of the chain must be at the same horizontal plane, see picture from SonicSam.

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Originally posted by Volv
If that was a parameter of SonicSam's question then yes, you are absolutely right

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Mathematically it is true that if both ends of the chain are on the same horizontal plane then there will be no net force, hence no movement.

Cookie is also correct when he says that a system in which the chain is joined makes no difference to the model whatsoever given that the ends of the sloped surface are on the same horizontal plane -- and as there is no net force to start with (whether the chain is joined or not) then there will be no movement.

If they were not on the same horizontal plane then yes, there may be a net force on an un-joined chain. However, if the chain is joined then unlike the previous example, there is not an even distribution of the hanging chain between the two sides (since the surface is not on the same horizontal plane, there will be more hanging from the shorter side), this uneven distribution acts to negate any net force which may have existed in an unconnected chain and as such there will still be no movement in a circular chain.

Are you saying that when the surfaces end at the same height the angle of the first slope will allways cancell out the size of the chain on the second slope?

So none of these would move?

Because that was whut i was thinking...

however i think the green chain doesn't prove anything, using that no chain would ever move... so in this case it doesn't change anything but it doesn't prove anything either

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Originally posted by billyy
Are you saying that when the surfaces end at the same height the angle of the first slope will allways cancell out the size of the chain on the second slope?

So none of these would move?

Because that was whut i was thinking...

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That's what the maths says

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Originally posted by billyy
however i think the green chain doesn't prove anything, using that no chain would ever move... so in this case it doesn't change anything but it doesn't prove anything either

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Yep, a round chain wouldn't move in any situation. However when the surfaces end at the same height then there's no net force on the green part below, therefore if there's a net force on the red (top) part, then it would cause it to move. Given that, and since we know the linked chain won't move on its own there must therefore be no net force on the top (red) part.
I think that's what Cookie is trying to say anyway.

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Originally posted by Volv

quote:

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Originally posted by billyy
however i think the green chain doesn't prove anything, using that no chain would ever move... so in this case it doesn't change anything but it doesn't prove anything either

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Yep, a round chain wouldn't move in any situation. However when the surfaces end at the same height then there's no net force on the green part below, therefore if there's a net force on the red (top) part, then it would cause it to move. Given that, and since we know the linked chain won't move on it's own there must therefore be no net force on the top (red) part.
I think that's what Cookie is trying to say, and it's true.

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exactly... and no maths or equations involved here...

PS: will you be my personal thought translator? I'll even pay you


PS: what Volv said is almost exactly the same as what I've said the first time though... but oh well...

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Originally posted by Volv
Yep, a round chain wouldn't move in any situation. However when the surfaces end at the same height then there's no net force on the green part below, therefore if there's a net force on the red (top) part, then it would cause it to move. Given that, and since we know the linked chain won't move on its own there must therefore be no net force on the top (red) part.
I think that's what Cookie is trying to say anyway, and it's true.

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quote:

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Originally posted by CookieRevised before people started to question each word
Think about it, what if you have something hanging from below connecting both ends of the chain. It would mean that there would be a 'force' pulling on each side equally from below no (so it doesn't matter if it is there or not)? So, if the top piece of the chain would move to some direction, it means the bottom part would move too (in the opposite direction). If that would happen, you would have a perpetual machine! Which isn't possible... hence, it would never move, no matter the angles and the lengths of the slopes, as long as both the 'bottom' parts are on a horizontal plane.

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