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phetsims / pendulum-lab

"Pendulum Lab" is an educational simulation in HTML5, by PhET Interactive Simulations.
GNU General Public License v3.0
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Easy to create infinite energy #90

Closed bryo5363 closed 8 years ago

bryo5363 commented 9 years ago

It is very easy to generate a large amount of energy. In doing this, the various energy values will fluctuate.

Steps to reproduce 1) open energy tab 2) move mass to make it oscillate 3) reduce the length of the pendulum at the minimum of the trajectory 4) keep repeating

recording 7

ariel-phet commented 9 years ago

The minimum length will change when we rescale a few things in the sim, hopefully will address this issue

jonathanolson commented 8 years ago

Not sure how changing the minimum length would prevent this, seems more like a design issue to me.

Energy now won't fluctuate with the new model.

If you want to keep energy constant while changing the length, the angle would need to change (if the pendulum is swinging up to 90 degrees on each side, increasing the length at 90 degrees would increase energy).

arouinfar commented 8 years ago

Now that @jonathanolson has fixed the model and adjusted the scale/zoom, I don't think there's anything else that needs be done to address this issue.

If you want to keep energy constant while changing the length, the angle would need to change (if the pendulum is swinging up to 90 degrees on each side, increasing the length at 90 degrees would increase energy).

It seems unphysical to try to hold energy constant while changing the length, so let's not go there.

Everything looks good to me in dev.6, and the energy no longer fluctuates, so I'll go ahead and close this issue.