* Inertia is the tendency of an object to resist changes in its motion.
* Mass is a measure of an object's inertia. The more massive an object is, the harder it is to get it moving or to stop it once it's moving.
Speed doesn't directly affect inertia. While a faster object has more momentum (a measure of its motion), its inertia remains the same.
In simple terms:
* A heavy truck is much harder to push than a small car, even if they are both standing still.
* A heavy truck is also harder to stop once it's moving, even if a small car is moving at the same speed.
Let me know if you have any other physics questions!
