When you use a crowbar to lift a large rock, you're working against the force called gravity.

Here's why:

* Gravity: This is the force that pulls everything towards the center of the Earth. The rock is being pulled down by gravity, and you need to exert an upward force to overcome it.

* Crowbar: A crowbar acts as a lever, helping you to amplify the force you apply. You apply a smaller force over a longer distance to overcome a larger force (gravity) over a shorter distance.

Let me know if you'd like to explore other forces involved in using a crowbar!