Tutorials/Falling blocks

FallingSand has two important NBT Tag fields that change the appearance, movement, and lifetime of the entity.

Most notable of the is BlockID. Using a BlockID for FallingSand in /summon grants the player the ability to, for example, create a falling bedrock block. ('/summon FallingSand ~ ~ ~ {BlockID:7}'). Note that even though as of 1.8 Minecraft has moved to item ID's of 'minecraft:stone' etc., the BlockID still uses the number format.

The other important tag is Time. Time stands for the time (in ticks) for how long the FallingSand has existed. If 0, the entity despawns, if 1 or greater, will continue ticking up, until it reaches a maximum lifetime. This means if the player wants to have a falling bedrock block that does not despawn immediately, then they should put that in the NBT tags ('/summon FallingSand ~ ~ ~ {Block:"minecraft:bedrock",Time:1}'). When the maximum lifetime is achieved, the FallingSand will despawn and drop the block as an item (unless it's a liquid, a block that doesn't have an item form with the same id, or the data tag  is set). The maximum lifetime cannot realistically be reached from  unless the FallingSand is riding another entity (in which case it isn't falling, but its time is still ticking) or is high above the world.