Loretta Mitchell, age 14, of Reno, Nev., for her question:

WHAT CAUSES VISCOSITY?

Viscosity is a property of fluids that causes them to resist flowing. It is caused by internal friction from the fluid's molecules moving against each other.

All fluids have some degree of viscosity. Fluids with high viscosity, such as molasses, flow more slowly than those with low viscosity, such as water.

The viscosity of motor oil determines how effectively it can lubricate the parts in an automobile engine.

Molecules in liquids interact more as the temperature decreases. C Hot liquids, for example, have lower viscosity than cold liquids. The more strongly a fluid's molecules interact, the more viscous the fluid. The larger the size of a molecule, the greater the interaction.