Final answer:
Water moves up the paper towel by capillary action.
Step-by-step explanation:
To answer your question, water moves up the paper towel by capillary action. Capillary action occurs when a liquid flows within a porous material, such as a paper towel, due to the attraction of the liquid molecules to the surface of the material and to other liquid molecules. The adhesive forces between the water and the paper towel, combined with the cohesive forces within the water, are strong enough to move the water upward against gravity.