Archive for August, 2009

Einstein the sailor

Monday, August 31st, 2009


Einstein owned and sailed a number of boats. This one was on Saranac Lake in upstate New York.

Air and Water

Thursday, August 6th, 2009

Air and water are the sailor’s fluids. (Alcohol doesn’t count.) Just two numbers determine the intrinsic properties of these fluids.

PROPERTY #1: The density is a measure of a mass of a given volume of the fluid. Water has a density of 1000kilograms per cubic meter. Water is about 800 times as dense as air.

Density is more precisely defined by;


PROPERTY #2: The kinematic viscity is a measure of fluid friction. Viscosity slows fluid motion. The larger the kinematic viscosity, the more quickly the motion stops. Air’s kinematic viscosity is about 15 times as large as that of water. Fill a hollow globe half way up with water and rotate it so the air and water inside are spinning. Stop the globe and the air’s friction will stop the air much faster than the water’s friction will stop the water. The magnitude of air’s friction is smaller, but its density is so small that it takes very little force to stop the spinning.

Lord Kelvin’s Sailboat

Sunday, August 2nd, 2009


In 1870 at the age of 46, Lord Kelvin (or William Thomson or Baron Kelvin of Largs) was delighted with his purchase of a 126 ton yacht, the Lalla Rookh. This boat was both a pleasure craft and a floating laboratory.