Falling Block

A falling block is the entity form of block that appears when a gravity-affected block loses its support.

Spawning
Falling blocks naturally spawn where gravity-affected blocks lose their base of support. These blocks include:

Although the same appearance as its corresponding block and affected by gravity, the primed TNT entity is not a falling block.

If cheats are enabled, falling block entities can be spawned using the command. By tweaking the  NBT tag, it is possible to summon a falling block entity that normally does not fall as a block, such as dirt or stone, although it will have the same behavior as a naturally spawned falling block.

Behavior
A falling block continues falling until it lands on another block with a solid top surface. If it lands with the bottom center of its hitbox on a replaceable block (grass, water, vines, air, etc.) then the falling block returns to its block state. Otherwise, it breaks and drops as an item.

Like most other entities, falling blocks are affected by explosions and bubble columns, can be launched by a moving slime block, can be pushed by pistons, can be slowed down by cobwebs, and can slide down the side of a honey block. However, they do not bounce on a stationary slime block and can neither be pushed nor slowed down by water or lava.

Falling blocks pass through most entities without colliding with them, although projectiles such as arrows bounce off them. They do not have health, cannot be attacked and do not take damage. They are also immune to all status effects.

A falling block that has been in the air for 25 seconds will destroy itself and drop as an item.

Commands such as can change the moving and facing directions of a falling block, although there are no in-game mechanics that can alter a falling block's facing direction. They can be removed with the command.

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