Since browsers do no longer support applets, the PhysBeans simulations have to be migrated to other technologies. Some results of the efforts are shown here.
A simple way to make applets work again is using Java Web Start. This is possible with only minor adaptations to the existing code. Two examples are shown here:
To make this work, you may have to change the Java security configuration. In case of trouble start the Java Control Panel, open the Web Settings Tab and add the PhysBeans base URL http://www.peter-junglas.de/fh/physbeans/ to the Exception Site List.
In any case you will have to go through some intimidating warning tabs and confirm that you are willing to throw security over board. Don't be afraid, the PhysBeans applets do no harm. In any case you can restrict the execution to a sandbox, which is reasonably safe and works with PhysBeans.
A completely different approach: The applets can be rewritten using libGDX, which allows to create a JavaScript version and an Android app automatically. This is highly experimental - use at own risk.