On Physics

Syntaxes	Version
[block] physics	1.4.6

Called when a physics check is done on a block. By cancelling this event you can prevent some things from happening, e.g. sand falling, dirt turning into grass, torches dropping if their supporting block is destroyed, etc.Please note that using this event might cause quite some lag since it gets called extremely often.

Exemples:

on block physics:
    block is sand
    cancel event