pixelzoom
commented
3 years ago @Nancy-Salpepi thanks for reporting.
The molecule rotates into alignment with the electric field at an angular velocity that is linearly proportional to the magnitude of the molecule's dipole. So the greater the magnitude of the molecule dipole, the faster the molecule will rotate into alignment with the electric field. In the case you've configured, the molecule dipole has a very small magnitude, so it therefore has a very small angular velocity, and will take a long time to rotate into place. This is not a bug, it's physically accurate.
The change in angle is computed in MPModel.js, in the updateMoleculeOrientation method:
// magnitude of angular velocity is proportional to molecular dipole magnitude
const deltaDipoleAngle = Math.abs( Utils.linear( 0, MPConstants.ELECTRONEGATIVITY_RANGE.getLength(), 0, MAX_RADIANS_PER_STEP, dipole.magnitude ) );where ELECTRONEGATIVITY_RANGE is [2,4] and MAX_RADIANS_PER_STEP is MAX_RADIANS_PER_STEP is 0.17 radians. So at it's fastest, the molecule will rotate ~36 degrees per animation frame.
Options:
(1) Do nothing. The current behavior is physically accurate, and is therefore a good learning experience. If it's rotating too slowly, make the molecule dipole larger and it will rotate faster.
(2) Change the computation of deltaDipoleAngle so that any non-zero molecule dipole has some minimum angular velocity. Use a value that results in a slow rotation, but doesn't take 10 minutes to rotate into alignment with the electric field. This will NOT be physically accurate, as molecules with different (small) molecule dipoles will have the same angular velocity.
My recommendation is option (1).
@arouinfar how would you like to proceed?
arouinfar
Test device iPad
Operating System iPados 14.7.1
Browser safari
Problem description https://github.com/phetsims/qa/issues/680
After creating a linear nonpolar molecule, when the molecule is positioned horizontally in the electric field, it can sometimes take over 10 minutes for the molecule to move to a vertical position (see highlighted times in screen shots). I noticed that by slightly moving the A or C atom, with the molecule still appearing to be linear, the speed of rotation can be changed. I was also able to reproduce this with my Mac 11 + chrome, but with some difficulty (video).
Steps to reproduce
Visuals iPad: You can see in the screenshot that is was 9:25 when I placed the molecule in a horizontal position
The time was 9:43 when it reached a vertical position.
In this video, you can see that I was able to adjust the molecule so that the speed is so slow it doesn't even look like it is moving. (The gif was too large so I made a movie of my movie!) https://drive.google.com/file/d/1oVsjkNXy3hS8WScrBqzEll5KPo1OQyej/view?usp=sharing
Troubleshooting information: !!!!! DO NOT EDIT !!!!! Name: Molecule Polarity URL: https://phet-dev.colorado.edu/html/molecule-polarity/1.2.0-dev.3/phet/molecule-polarity_all_phet.html Version: 1.2.0-dev.3 2021-07-26 23:04:53 UTC Features missing: applicationcache, applicationcache, touch Flags: pixelRatioScaling User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/92.0.4515.131 Safari/537.36 Language: en-US Window: 1167x687 Pixel Ratio: 2/1 WebGL: WebGL 1.0 (OpenGL ES 2.0 Chromium) GLSL: WebGL GLSL ES 1.0 (OpenGL ES GLSL ES 1.0 Chromium) Vendor: WebKit (WebKit WebGL) Vertex: attribs: 16 varying: 31 uniform: 1024 Texture: size: 16384 imageUnits: 16 (vertex: 16, combined: 80) Max viewport: 16384x16384 OES_texture_float: true Dependencies JSON: {}