When you try to lose weight, what you are really trying to do is
lose fat. Weighing yourself is a first approximation of your
progress, but a better indicator is your body fat percentage
(%BF). Unfortunately, measuring %BF can be expensive and/or
difficult. It doesn't need to be so. All you need is a body of
water (e.g. a swimming pool), a gallon jug, and your bathroom
scale. One of the most accurate ways to measure body fat is
hydrostatic weighing. You are weighed underwater and on land,
and your body's density is determined. Then body fat is
estimated from the measured density. This is the same basic
technique that we will use, but we don't require an underwater
scale or special tank. First the how, then I'll give you the
physics. Get in the pool and exhale all the air you can, and
allow yourself to sink. You will sink unless you're particularly
obese. Take note of the sensation of sinking. Then do the same
thing but with your lungs full. Take note of the sensation of
floating. Now, we want to reach the poi