- #1
nothingislost
- 8
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A mass hangs on a string and is struck by a horizontal impulsive force that introduces an angular velocity w, using a lagrangian multiplier what are the conditions that causes the string to go slack.
the constraint is simply that the string is of constant length and therefore the radius of motion is of constant distance, r=a. I write the lagrangian equations for r and theta and then solve for the constraint force/multiplier. for the string to go slack the constraint force in r goes to zero and therefore lambda goes to zero.
solving for theta dot or omega i get that the condition for a slack string is that w=sqrt (g/a)
This doesn't make sense however as this is the condition when theta is at 180 and by logical reasoning i know that the string starts to go slack when theta max is just over the horizontal or 90.
What am i doing wrong here and how do i account for the fact that this is a string and not a solid rod?
thanks :)
the constraint is simply that the string is of constant length and therefore the radius of motion is of constant distance, r=a. I write the lagrangian equations for r and theta and then solve for the constraint force/multiplier. for the string to go slack the constraint force in r goes to zero and therefore lambda goes to zero.
solving for theta dot or omega i get that the condition for a slack string is that w=sqrt (g/a)
This doesn't make sense however as this is the condition when theta is at 180 and by logical reasoning i know that the string starts to go slack when theta max is just over the horizontal or 90.
What am i doing wrong here and how do i account for the fact that this is a string and not a solid rod?
thanks :)
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