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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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Friction is always present even when friction is set to none #105

Closed orejolaphet closed 8 years ago

orejolaphet commented 9 years ago

Noted in Issue #82

If you zoom in the the energy graph 50+ times you will eventually see some friction in the system during oscillation even though friction is set to none. (Note the smaller the angle the more you must zoom in)

To reproduce: Open sim Select seen w/ energy graph Open energy graph Click zoom 50+ times Move mass to large angle and begin oscillation

At small angles screen shot 2015-06-22 at 11 57 05 am

At Large angles screen shot 2015-06-22 at 12 00 26 pm

orejolaphet commented 9 years ago

Weirdness. If you leave the page for a period of time the friction is no longer displayed.

andrey-zelenkov commented 9 years ago

Same behavior you can see for the original Java simulation. It's a feature of selected mathematical model.

orejolaphet commented 9 years ago

@ariel-phet what do you think about this behavior?

ariel-phet commented 9 years ago

Seems like something we will need to address internally

jonathanolson commented 8 years ago

Right now the "thermal energy" is calculated as "total energy - kinetic and potential energy", which causes any inaccuracies and cumulative errors to be added to the thermal energy.

http://www2.phy.ilstu.edu/~rfm/380s13/chapters/CH2.4_Pendulum.pdf notes a differential equation for the change in kinetic/potential energy, which could be approximated on its own at every step.

@ariel-phet, does this seem like a good approach?

jonathanolson commented 8 years ago

Reassigning for a response to the above comment.

ariel-phet commented 8 years ago

In our discussion I think we agreed on the above approach.

jonathanolson commented 8 years ago

Forgot this on my list of things that were fixed by the model updates.