We will be upgrading the PhET server on Friday, April 19 at 5:30 PM Mountain Daylight Time. During this time, PhET (http://phet.colorado.edu) will experience periods of unavailability. We expect that the outage will last only 30 minutes and that we will be back online very quickly. However, if you experience issues, please e-mail the PhET Help Desk at firstname.lastname@example.org.
Thanks for your patience during our system upgrade.