Minecraft wiki entry for Sand, associated text: If a block of sand has snow on it and is made to fall, the snow is destroyed‌[Java Edition only] and does not drop snowballs.
Since falling sand is considered an entity, it can be launched in a TNT cannon, similar to an ignited piece of TNT.
Sand falls at the same rate when submerged in water, or lava, or air.
If a player is standing on a stack of sand or gravel, and the stack falls onto a non-solid block, the player can fall fast enough to take damage or even die.
Sand falls through torches without breaking, if there is air below the torch.
Sand and gravel take about 0.45 seconds to fall one meter.
The sand texture is rotated if a block of sand turns into a falling_block entity, similar to ignited TNT blocks. This is not the case with gravel.
Since falling_block is considered an entity, blocks of sand without supports may disappear for a split second and a falling_block entity is summoned. This is also the case when it's landing, but the entity (not the block) disappears instead before a block is placed.
Sand or gravel placed on top of a 2-block-high plant floats in the air until receiving a block update. This glitch was removed and later restored intentionally.