Is momentum how difficult it is to stop an object?
Much appreciated
Thanks:)

Also known as INERTIA

ANY object with even a SMALL mass will maintain the existing direction AND velocity until acted upon by some force.

The degree to which the velocity and direction are changed with will be in proportion to the magnitude of the force and inversely proportional to the object's mass.

A force CAN NOT be applied to ANY object without applying an equal and opposite force to SOME other object.

Search Wikipedia or your other preferred reference for: Newton's laws of motion

Inertia is a principle and is not quantifiable. Momentum is quantifiable however, the two are not the same thing.