Adhesion is the sticking together of different materials or substances. When you press a piece of tape onto paper, adhesion is what makes it stay put. The tape and paper are two different materials, and adhesion is the force holding them together.

Scientists distinguish adhesion from cohesion, which is when the same material sticks to itself (like water molecules clinging to each other in a drop). Adhesion happens between different things: a sticky note adhering to a wall, a gecko's feet adhering to glass, or wet paint adhering to a fence.

Understanding adhesion helps engineers create better glues, bandages, and coatings. It explains why some materials stick together easily while others slide right off. When you try to get honey off a spoon, you're fighting adhesion between the honey and the metal. When you lick an envelope to seal it, you're activating adhesion between the glue and the paper.

The strength of adhesion depends on the materials involved and their surfaces. Rougher surfaces usually create stronger adhesion because they have more area touching. That's why sandpaper helps paint adhere better to wood: it creates tiny grooves for the paint to grip.