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.

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