Increase Fast time speed for Single Particles screen

[matthew-blackman]

In student interviews, none of the users got to see an interference pattern on the Single Particles screen unless prompted. To help fix this, I'd like to increase the 'Fast' speed on this screen.

The purpose of the 'Fast' time speed on the Single Particles screen is to see a pattern of hits build up more quickly. With the current time speed value, it still takes over a minute to see a pattern emerging. I don't see any drawbacks to doing this, since 'Fast' mode is not meant to be used for making out the details of the wave behavior.

I'll self-assign this and then ask @samreid for a review.

[samreid]

https://www.w3.org/TR/UNDERSTANDING-WCAG20/seizure-does-not-violate.html

[matthew-blackman]

This has been updated and is working well in testing. The buildup of a pattern is fast, but the wave packets are still visible as they quickly move across the screen.

One remaining question is whether this is WCAG compliant based on the guidelines @samreid linked above. It is definitely happening more than 3 times/second, but @terracoda said that she isn't sure that this behavior constitutes the kind of 'bright flash' that the WCAG guidelines are referencing. She also mentioned that this is an 'opt-in' behavior, and the sim doesn't need to be put on fast speed (it would just take longer to see a pattern build up).

I'd like to get sign-off on this from the broader design team before closing this issue.

[matthew-blackman]

The design team discussed the WCAG concern around the updated Fast behavior on the Single Particles screen.

Although more than three particles per second may be emitted in Fast + Auto-fire mode, we do not think this behavior constitutes a problematic full-screen flashing effect under the WCAG Three Flashes or Below Threshold criterion:

• The visual behavior is a rapid traversal of individual wave packets across the screen rather than the screen itself flashing.
• Each wave packet occupies only a limited portion of the screen and appears to remain below the applicable area threshold.
• Fast mode is optional and is not the default. Users can select Normal or Slow mode instead.
• There are additional workarounds, such as using a teacher-created preset in which the interference pattern has already been built up.

As an additional precaution, we agreed to add a note to the Teacher Tips document so teachers are aware of the rapid visual behavior in Fast mode. We may also consider documenting this in the Essential Exceptions material, although we have not yet determined whether that is the appropriate location.

@kathy-phet, could you please provide final approval/sign-off on this approach? Once approved, I think this issue can be closed.