Do you weigh more if you put your scales on a carpet than
you do if they?re on a tile floor? This is a long-standing
controversy among dieters. Now researchers say it?s true?
you really do seem to weigh more if you put your scales on a
carpeted surface.
David MacKay, a physicist at the University of Cambridge,
heard about this controversy by chance, while talking with a
friend. "I was just chatting to her and she said, 'You're a
physicist. Why do you weigh more on carpet than on a hard
surface?' I didn't have a clue, but it seemed like a good
question to throw at an undergrad," he says.
So MacKay and his student Jon Pendergast brought in some
standard bathroom scales and tried them out on different
surfaces. They found they weighed about 10% more when
the scales were on thick carpet than on a hard floor.
So what causes the ?carpet effect?? Pendergast took several
scales apart and measured the movement of their internal
mechanisms when they were placed on various surfaces. He
discovered that inside each set of scales are four levers or
fulcrums, each pointing inwards from one corner. These
transmit the weight of the person standing on the scales to a
spring-loaded metal plate at the back. The movement of the
plate is then transferred via a metal rod and turns the dial on
the scales.
On a hard surface, the base of the scales bows slightly,
making the fulcrums at each corner of the scales tilt in. This
shortens the distance between each fulcrum and the point at
which the load pushes onto the metal plate.
When you put the scales on a deep carpet, however, and the
scales sink down into it, so the carpet supports the base,
preventing it from bending. This increases the distance
between each fulcrum and the metal plate, so the same
weight causes the lever to move further. Even a small
increase in this distance can add several pounds to the
weight registered on the scales.
But which weight is your real weight?the one you read on
carpet or tile? That?s what dieters want to know. MacKay
asked manufacturers and found out they make their scales
so they read your correct weight when placed on a hard
surface, not a carpet, because most people put them on a
tile floor.
"I've always thought this was an urban myth," says a
spokeswoman for Weight Watchers. "But it sounds like it
makes a huge difference."
What other signs are you reading wrong? To find out,
get ?Signs of the Times? by Ray Grasse, who will be on
Dreamland July 6,click here.
For more information, click here.
