The adhesive on sticky tape is a viscoelastic material, meaning that it behaves both like a solid and a liquid. When you apply pressure to it, it flows like a liquid, finding its way into any tiny gaps in the surface it is being stuck to. Then, when you leave it alone, it turns back into a solid, allowing it to lock into those gaps like a piece of a jigsaw puzzle to hold itself in place. However, before you even apply any pressure, another force has already got to work.
The molecules of the adhesive are dipoles, meaning they have one positively charged side and one negatively charged side. This makes the molecules act like tiny magnets, creating an electrostatic attraction when they come into contact with another surface. These weak sticking bonds are known as van der Waals forces, which are also used by geckos to stick to walls. When you peel off the tape, this bond is broken, but will continue to work again and again until the adhesive surface gets too clogged up with dust and dirt.
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