Any proof?

[ltseung888]

Dear Parisd,

There are NO mistakes.  Please double and triple check.

[eatenbyagrue]

Dear Parisd,

There are NO mistakes.  Please double and triple check.

parisd actually got it right.  I double and triple checked.


First of all, you are wrong when you say that the tension in the string does work.  As we all know from high school, string tension can only perform work along the string.  With the pendulum, by definition, the tension in the string is always exactly perpendicular to the motion of the bob, so the string tension cannot perform any work at all.


parisd is also correct in pointing out the flaws in your calculations.  For some reason not clear to me, you conclude that the total work done is the horizontal displacement plus the vertical displacement.  Assuming zero friction (as you do), the amount of energy required to move a bob purely horizontally (that is, sideways to force of gravity) is very near zero.  So the only real work done is the vertical component of the bob's motion.


Per your calculations, this is about half of the force that is exerted, which makes no sense.  So there is a mistake in your equation, and the mistake is not in your favor.  I do think some kind of integration is in order, as the force required to move the bob along its plane increases exponentially with the angle of incline.  This is not a linear function, as your equations imply.


Finally, and this probably does not make too much difference in moving the bob 9 degrees, your application of the purely horizontal force is an inefficient way to raise the bob.  The most efficient way to apply force would be in a direction perpendicular to the string.  As you would not be wasting energy fighting against the string.  As an example, imagine the bob at 89 degrees.  A  purely horizontal push on the bob would be expending 89/90 of its energy just applying more tension to the string, and only 1/90th of its energy actually raising the bob.  In fact, given a nonzero mass, it is theoretically impossible to raise bob to exactly 90 degrees while applying only horizontal pressure.

[ltseung888]

Looks like there are many non-physicists who got themselves and others confused.

Rather than me giving the same explanation again, I shall wait for some other scientists or engineers to comment.

There are NO mistakes.  But it is good for everybody when someone raise questions.  All can learn.

[eatenbyagrue]

Looks like there are many non-physicists who got themselves and others confused.

Rather than me giving the same explanation again, I shall wait for some other scientists or engineers to comment.

There are NO mistakes.  But it is good for everybody when someone raise questions.  All can learn.

I disagree.  I think you have made a mistake.  But I am willing to stand corrected if shown a pendulum in perpetual motion, as you assert.  I love learning new things.


I do think your calculation of horizontal work is at the crux of your error.  You are counting the vertical work double.  You count it as part of the horizontal, and then also as part of the vertical.  There is only one bit of work done, and that is rasing the bob against gravity.  Everything else is just (almost, if not for slight friction) effortless motion that does not constitute work.


I've googled some of your older posts, and it appears you have been taking this position for many years now.  This makes me think what I am writing here is wasted effort, as you obviously have seen this criticism before and have not been convinced by it.  Good luck, though.

[parisd]

Lsteung888,

No need to double check, your overunity calculation mistake is obvious.

But prove me wrong by lifting the pendulum to an angle of 9.46 degree (or whatever you wish) using an horizontal force then please do show us overunity; just make a video of any pendulum that has been raised to X degree then just let it go, it will oscillate and due to calculated overunity of 1.5 on the other side should raise more than -X degrees, easy to prove if yes or no you are right. I bet it will stop at -X degrees or slightly less.

Good continuation but please dont confuse people with wrong statement on OU, we are here to find the real thing.