|Feb27-13, 03:19 AM||#18|
A General Question about Tension
So your only question is about where 'extra' forces seem to come from. Asking that question, as already mentioned, implies that there must be some conservation law for forces. But there isn't, so there is no point in asking where the forces 'come from'.
If you were actually constructing that setup, you would need to do some work in pulling the suspension string sideways from vertical. That work would be raising the level of the suspended mass from where it was originally hanging (that's where energy conservation would come in - does that help you in any way?). But problems like this, involving forces in equilibrium do not consider how the situation was arrived at.
I remember, at A level, a very long time ago, in 'Applied Maths', we solved some such problems using the principle of 'virtual work', in which you distort a framework, infinitessimally, and calculate the work done. You turn this into an equation, which solves the network for you. Don't ask me to repeat it - the last time I did it would have been 50 years ago.
|Feb28-13, 10:25 AM||#19|
You know, a lever can be used to lift a heavy weight with a light force. Where does the extra force come from?
See this: http://en.wikipedia.org/wiki/Mechanical_advantage
It is not force that is conserved, but force over distance. If you remove the string 1, the weight will drop. Due to string 2, it must move a larger distance to drop the same amount of height. If you think about it, this effect exactly accounts for the mechanical advantage.
|Feb28-13, 01:14 PM||#20|
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