• Cohesion causes water to form drops;
• Durface tension causes them to be nearly spherical;
• Adhesion keeps the drops in place;
• Gravity enables the water drops to fall to ground;

• Mechanical adhesion - Materials fill the voids of the surfaces to hold them together by interlocking.
• Chemical adhesion - Materials form a compound at the join.
• The strongest joins, ionic bonding or covalent bonding.
• A weaker bond, through hydrogen bonding.
• Electrostatic adhesion - Conducting materials pass electrons to form electrical charge at the join.
• Diffusive adhesion - Materials merge at the joint by molecular diffusion
• polymer chains where one end of the molecule diffuses into the other material.
• sintering. When metal or ceramic powders are pressed together and heated, molecule diffuse from one particle to the next.

A physical property of a substance, caused by the intermolecular attraction between like-molecules.

What makes an interaction strong? Material types and contact surface area

Cohesion, along with adhesion, helps explain phenomena such as surface tension and capillary action.

1. The force resisting the relative motion of two surfaces in contact (solid, liquid and gas).

2. Not a fundamental force

• derived from electromagnetic forces between atoms and electrons;
• cannot be calculated from first principles;
• must be found empirically.