For our purposes, slime will be defined as any non-Newtonian fluid. If this term sounds hopelessly technical, please read on— it is actually quite simple to understand! To understand what this term means, it is impor- tant to examine the theories of Isaac Newton (1642–1727), one of the greatest scientists who ever lived. He made many revolutionary discoveries in the fields of mathematics, motion, and gravity. But he also did a lot of work with fluids.
Newtonian fluids and viscosity
Newton observed that the viscosity of fluids is affected only by temperature. Viscos- ity refers to a fluid’s resistance to flow. The more viscous a substance, the slower it flows. Ketchup is more difficult to pour than water, because ketchup is more viscous. And peanut butter is more viscous than ketchup. It is important not to confuse viscosity with den- sity. Oil is usually more viscous than water, yet oil is less dense and floats on top of water.
If a fluid is heated, it tends to become less viscous, and if cooled, it tends to become more viscous. The colder the temperature, the more viscous the fluid becomes, hence the saying “slower than molasses in January”. As the temperature drops, your car may be
more difficult to start because the
engine oil has become more viscous.