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Imagine trying to stir a spoonful of honey, then doing the same with water. The honey resists your spoon more, hinting at its higher viscosity. Viscosity is essentially a liquid’s reluctance to flow, often perceived as 'thickness'. Factors like temperature and molecular size affect it, but the key influence comes from the strength of intermolecular forces.

Think of molecules in a viscous liquid as friends holding hands in a crowded room; they move together and can't quickly navigate through the space. In less viscous liquids, it’s more like acquaintances in an open park, freely walking past each other. Strong intermolecular forces, such as hydrogen bonds, act like strong handshakes keeping the molecules together, resulting in a higher viscosity.

Diving into the world of intermolecular attractions, hydrogen bonding stands out for its strength and specificity. It's a strong type of dipole-dipole attraction that occurs when a hydrogen atom, covalently bonded to a highly electronegative atom like oxygen or nitrogen, is attracted to another electronegative atom.

These bonds are relatively stronger compared to other dipole-dipole interactions and can play a significant role in the physical properties of a substance. For instance, water's relatively high boiling point for its molecular weight can be attributed to hydrogen bonding. Substances with hydrogen bonding often have higher viscosities; they're like a group with a strong sense of unity, tougher to separate than those with weaker linkages.

The physical properties of substances such as boiling point, melting point, and solubility are profound indicators of intermolecular forces at play. As the forces increase in strength, so does the energy required to alter these properties. For instance, a high boiling point suggests strong intermolecular forces keeping the molecules together, requiring more heat energy to break them apart and transition from liquid to gas.

The intriguing dance between molecules' attraction to each other and their desire to move freely gives each substance its unique characteristics. It's why oil and water don't mix well or why ice floats on water. These characteristics affect how substances behave alone and in mixtures, defining uses in cooking, industry, and nature.