Final answer:
A handkerchief absorbs sweat due to its fabric material, usually cotton, which has many microscopic spaces in between fibers. Sweat is absorbed into these spaces by capillary action, the same principle used by plants to draw up water.
Step-by-step explanation:
A handkerchief is able to absorb sweat due to its fabric material - typically cotton or another absorbent material. These materials have a large number of tiny, microscopic spaces in between the fibers. When sweat comes in contact with the handkerchief, it moves into these spaces by the process called capillary action.
Capillary action is the ability of a liquid to flow in narrow spaces without the assistance of external forces like gravity. It's the same principle that allows plants to draw up water from the ground. Because sweat is a liquid, it's absorbed by the fabric of the handkerchief through the same process. Therefore, when you are sweating, you can use a handkerchief to wipe and absorb the sweat.
Learn more about Capillary Action