Open the simulator at https://phet.colorado.edu/en/simulation/energy-skate-park (Links to an external site.)
PhET Quick Tips: Java Troubleshooting for Mac :
https://www.youtube.com/watch?v=GpRqht0o4w4 (Links to an external site.)
PhET Quick Tips: Java Troubleshooting for Windows :
https://www.youtube.com/watch?v=bCpwWtA2Fe4