Straight Dope know stuff. And what they don't know, they'll make a guess at, for instance that the "H" in Jesus H Christ stands for ""Haploid"...This is an old bio major joke, referring to the unique (not to say immaculate) circumstances of Christ's conception. Having no biological father, J.C. was shortchanged in the chromosome department to the tune of one half...".
The people who contribute to Notes and Queries know stuff too. In answer to "I'm fascinated by the German ability to capture in one word a complex feeling that would require at least a sentence in English, like schadenfreude or weltschmerz. Are there any other good ones? ", someone suggested "Anschlusstreffer-- a goal scored when two down, bringing you within one of an equaliser. An equivalent English word might be "prequaliser""...
And of course, New Scientist know stuff: "Have you ever stood on your bathroom scales and leaned forward. It's great for dieters because you seem to lose a few pounds. On the other hand, don't swing your arms upwards because that way you will seem to gain weight. As all your weight is still carried by the scales irrespective of your position, why does this happen?" ...I'm going to give their full answer because of Jon's diet and the other recent food/weight posts:
"There are two reasons why a difference in weight might occur.
First, weighing machines with a square platform have only one weight detector, usually some form of a spring. The weight from above must be communicated to this spring equally, no matter where the load is on the plate. This is achieved by a system of levers that support the plate at four symmetrically located points. The levers also reduce the force applied to the spring so that it does not need to be too large. If some of the levers are not quite the right length, then a load placed at one side of the scales might result in an incorrect force being applied to the spring.
Early weighing machines such as beam scales avoided these problems by using plates suspended below a single support, so no matter where the load was placed, the plate swung until the centre of gravity was vertically below the support. Until quite recently high-precision balances still used the beam scale principle.
The second possible reason for error is that the bathroom scales are sitting on a soft carpet. As you move from end to end the scales tip. The scales measure the force being applied perpendicularly to the plate, and this decreases as you tip the scales away from the horizontal.
The answer to the second part of the question, regarding swinging your arms, is that this is a dynamic effect. As you accelerate your arms upwards your body will exert a greater force on the scale, proportional to the acceleration of the arms and their mass, and equal and opposite (that is downwards) to the force necessary to produce the acceleration. As soon as the arms stop accelerating, the force disappears.