The most common simple machine used for splitting things apart is a wedge.

Here's why:

* Wedge: A wedge is a simple machine that is essentially two inclined planes placed back to back. The force applied to the wide end of the wedge is concentrated on the narrow end, creating a greater force that can split things apart. Think of an axe splitting wood, or a chisel carving stone.

While other simple machines might be involved in splitting things apart, the wedge is the primary force behind the action.