# Trivia Testers : On Thin Ice

What is the meaning of those cryptic numbers used to identify engine oil?

1. the range of freezing temperatures
2. a range of viscosities
3. its range of operating temperatures in degrees C, divided by 10
4. the range of densities in grams per deciliter

On Thin Ice
A pilot of an airplane without floats would be glad to have a frozen lake to land on, if that engine (or engines) ever quit while out of reach of land. But if heat rises, then why does ice form first on the surface of lakes, ponds, rivers, and even oceans?

1. It is because evaporative cooling releases about 540 times the heat of a one Centigrade degree warmer parcel of water, per gram (despite radiative heating from the sun).
2. Due to the viscosity of water, mixing doesn’t occur to any significant degree, and the latent heat of cooling (the same excuse as in the previous choice) functions to reduce the surface temperature, first.
3. Water actually contracts as it cools, becoming more dense (not less dense, as you would expect from having seen everything from icebergs to the ice cubes in your drink). However, that is only up until the point where it cools to four degrees Centigrade (about 39 degrees Fahrenheit). After that, it expands, becoming less dense, and rises to the surface. When it freezes, its density drops even more significantly (further assuring its higher status).
4. If water were absolutely pure, it would form at the bottom first. However, the vertical profile of particulates causes the freezing point to be lowered. This is greatest at the bottom, and least at the surface. This is true for lakes, rivers, and even oceans.

Tides
The oceans have tides, but do any other bodies of water have tides as well?

1. Only oceans have tides. Even the largest of the world’s lakes is too small to display tidal behavior.
2. Larger lakes can have tides as well, although they are measured in inches or fractions of an inch.
3. Tides are everywhere. All bodies of water have them in an absolute, theoretical sense (although for a small lake, they would not be measurable). So does the earth’s crust, and so does the atmosphere.
4. Tides are everywhere indeed. But even small lakes can have them.