Ah I see the problem. You've sent your sand particles to a display event, therefore they've left the event with the Particle Physics operator and so they're not affected by it.
You'll need to either move the Particle Physics operator into their display event, or keep them in the other event and not pass them through the Send Out test.
Any particle that you want to be included in the solver properly needs to be in an event with a Particle Physics operator.
Think of events like buckets, and particles like grains of sand....a grain of sand cannot sit in more than one bucket at the same time. This is different than something like TP groups, where particles can occupy multiple groups. Operators will only affect the particles that are in their event.
You'll need to either move the Particle Physics operator into their display event, or keep them in the other event and not pass them through the Send Out test.
Any particle that you want to be included in the solver properly needs to be in an event with a Particle Physics operator.
Think of events like buckets, and particles like grains of sand....a grain of sand cannot sit in more than one bucket at the same time. This is different than something like TP groups, where particles can occupy multiple groups. Operators will only affect the particles that are in their event.