Please help:) I'm completing a lab report on investigating cohesion. I have everything completed but I don't understand what my variables would be.

The experiment contains:

Place a clean dry penny on a flat surface.
Fill a small cup of water.
Use a dropper or a pipette to gently drop water onto the penny.
Record the number of drops made before the water spills off the penny.
Dry the penny and repeat steps 1–4. Do three trials.

may someone please explain to me what the independent, dependent, and controlled variables would be? Thank you :)