The resistance of an object to changes in its speed or direction is called inertia.

Here's why:

* Inertia is the tendency of an object to resist changes in its motion.

* Speed refers to how fast an object is moving.

* Direction refers to the path an object is traveling along.

So, inertia is the property that makes it harder to:

* Start an object moving (resistance to changes in speed from zero to something else).

* Stop an object that's already moving (resistance to changes in speed from something else to zero).

* Change the direction of a moving object (resistance to changes in direction).

Let me know if you'd like more details about inertia!