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Suppose I am going to the doctor's and I want to do either of the following

  1. Make myself lighter on the scale
  2. Make myself heavier on the scale

For 2), isn't it just relaxing and let your mass drop?

For 1) how could I do this? Should I maybe exert a force on a table close by? Will that force (from my hand) transfer to the scale?

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You should carry an extremely powerful electromagnet in a briefcase with a hidden switch, and place it on the floor next to the scale, with a hidden switch driven by a car-opener in your pocket, and turn on the magnet as soon as you get on the scale. But if your doctor is wearing a watch, forget about it. –  Ron Maimon Dec 18 '11 at 6:25
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2 Answers

up vote 8 down vote accepted

Lots of ways, none practical (except one).

  1. Inhale a lungful of helium prior to stepping on the scale (or conceal helium balloons in pockets or the like). This will have a tiny effect but at least your voice will be squeaky.
  2. As @FrenchKheldar said, push on a table or pull on a bar. Obviously cheating though.
  3. Install an absolutely gigantic magnet around the weighing area and use the field to partially levitate your diamagnetic body. This will probably have an undesirable effect on any scales made of metal, though.
  4. Weigh yourself on a scales located at the top of Mt Everest, on an airplane, or best of all, on the ISS.
  5. Similarly, weigh yourself deep in a mineshaft tunnelled into the Earth.

The practical way would be to increase your metabolic activity and decrease your caloric intake over a sustained period. That and take your keys out of your pocket.

Seriously - the scales measure the force applied, which under normal controlled conditions is determined by your mass. So changing your mass, i.e. weight, is the only surefire way to do this.

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(1) Seriously, you can pass out by doing this. And the paramedics will laugh at your squeaky voice. (4) The places on Earth with the lowest gravity are Zaire, Ceylon, and the Leeward Islands. Go to a doctor over there. –  rdhs Dec 18 '11 at 7:34
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As you mention for 1), the scale is measuring the force applied on it. When "letting your mass drop" your body experiences a downward acceleration. Consequently, the force applied on the scale will be decreased. This would last only as long as your downward velocity is increasing.

Eventually you have to stop though, and as you decelerate your downward motion (or, equivalently, accelerate upward), the scales must exert a greater force on you. Consequently, the value on the scales will be higher.

Try it on a scale, from a standup position, "let your mass drop" and stop when your knees are bent. You will see your weight decreases as you drop, then increases as you slow down to finally reach its normal value.

Similarly, pushing on a table or pulling on a bar above you will lighten the force on the scale, thus decreasing your weight.

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This is reversed. If you are accelerating downward, then the normal force applied by the scale is less than the force of gravity, so the scale will show a lesser weight than usual during this phase. –  Chris White Mar 18 '13 at 23:42
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