Weight and Mass, Revisited

As an example, suppose that you are buying groceries on a space station a distance of 1500 km above the Earth, and you see a special on cheese. You can get 2.2 lbs of cheese for $4.00 or you can get 1 kg of cheese for the same price. Which should you buy? The amount of cheese (eg the food energy it would provide if you ate it) is determined by its inertial mass. You know that on the surface of the Earth, 1 kilogram weighs precisely 2.2 lbs. However, on the space station, the gravitational acceleration is less than at the surface of the Earth. Thus, 1 kg of cheese weighs less on the space station than it does on Earth. Conversely, in order to weigh in at 2.2 lbs, you need more than 1 kg of cheese. At a height of 1500 km, the gravitational acceleration is down by a factor of two, so that 2.2 lbs of cheese has an inertial mass of 2 kg, and would weigh 4.4 lbs on Earth. So you should definitely by the 2.2 lbs of cheese for $4.00.

1999-09-29