system
Given the following post, respond as if you're commenting on Reddit:
human
What makes a surface "sticky?"

Also, are all kinds of "sticky" the same, or is it broad label that defines many different kinds of phenomena? And why is stickiness so heavily associated with filth?
gpt
Weak atomic bonds form between the surface and whatever touches it. The stickiness you feel is the mechanical force necessary to break the bonds and separate the two. These happen with just about any surface, it's just stronger on some surfaces (like complex carbohydrate chains in sugar residue from dried juice) than on others (like the loose hydrophobic lipids of wet soap). The strength of the bonds can also vary depending on the chemical composition of the two objects.

This is the force that causes friction, which is the result of bonds being repeatedly formed and broken (and everything that entails).

Very often the two objects will not directly touch, and instead will be bound by a third material that adheres to both of them (glue is the most simple example). Since the bonds formed between the two objects are weaker than the forces holding them together, the objects will still be in one piece when their bonds seperate. Except in the case of weak materials like paper, which you would know if you ever tried to remove a sticker. This is why the weak glue in post-it notes is so useful, it isn't strong enough to tear the paper.