Viscosity

fluids · physics · friction

Thickness in motion. Viscosity measures how much a fluid resists moving when you try to push it or pour it. Honey has high viscosity because its molecules stick together strongly, so it flows slowly, while water has low viscosity and pours easily.

Different causes. In liquids like honey, viscosity comes from molecules pulling on each other with attractive forces. In gases like air, viscosity happens because gas molecules constantly bump into each other as they zoom around.

All fluids have it. Every liquid and gas in the universe has some viscosity, except for one weird exception called a superfluid. This means that even the smoothest-flowing fluids still have a tiny bit of resistance built in.

Speed matters most. The faster you try to make a fluid move, the more it resists, and the resistance is directly connected to how fast the different layers of fluid are sliding past each other.