Could you weigh yourself with two scales?

[Leros]

I was reading the "I maxed out my scale" thread and I was wondering...

Say you did max out your scale. Would you get an accurate reading by getting two scales, putting one foot on each, and adding the results together?

 

[Alone]

http://www.ehow.com/how_5618945_weigh-foot-different-scale.html

 

[Leros]

Um, no.

Why not?

 

[Juked07]

Disagree with Alone

I think there's potential for error if you exert extra force in sort of a diagonal direction on each scale. Then the scales would have to exert extra normal force to hold you up. But most people don't stand like that.

 

[rcpratt]

I don't see why not.

 

[OCGuy]

The plane would take off...

 

[preslove]

I have to use 4 scales

 

[Leros]

It seems that a scale works by a spring resisting your weight. If you have two scales, the two scales together must be resisting your total weight. A unit of your weight being resisted by one scale, is already being resisted, so it will not be resisted by the other scale. So the total resistance is proportional to your total weight, so the sum of the two scales would be correct.

 

[Leros]

http://www.ehow.com/how_5618945_weigh-foot-different-scale.html

No fair, you changed your response when you realized you were wrong.

 

[Robsasman]

Isn't that how some truck weigh stations work. They weigh each set of axles separately.

 

[Alone]

No fair, you changed your response when you realized you were wrong.

As any reasonable person should.

Oh, wait, this is the Internet, I should have stuck to my guns!

 

[Leros]

Disagree with Alone

I think there's potential for error if you exert extra force in sort of a diagonal direction on each scale. Then the scales would have to exert extra normal force to hold you up. But most people don't stand like that.

Right. You still need the force to be as vertical as possible. You can't put the scales far apart and have your legs angled out.

 

[Leros]

As any reasonable person should.

Oh, wait, this is the Internet, I should have stuck to my guns!

No, this is the internet and I need to prove you wrong.

HEY EVERYBODY ALONE WAS WRONG!

 

[Alone]

Shhh!

 

[Leros]

The plane would take off...

So if you had a plane on two treadmills with built in scales....

 

[BlahBlahYouToo]

you would have to stand very still or take a snapshot of the reading on both scales.

 

[GodlessAstronomer]

Right. You still need the force to be as vertical as possible. You can't put the scales far apart and have your legs angled out.

No I think it would still work (if the free body diagram in my head is correct). As long as the scale can be relied upon to only measure vertical forces then the sum of the scales should be your weight. If the scale is mechanical in nature then the lateral forces probably add some friction to the system which would introduce inaccuracies.

 

[rcpratt]

Technically the normal force would be the same no matter what lateral forces you put on the scale...but I could see it messing with the scale depending on how it measured the force.

 

[ShawnD1]

Technically the normal force would be the same no matter what lateral forces you put on the scale...but I could see it messing with the scale depending on how it measured the force.

You can see how finicky a scale is just by standing in different spots. Stand on it normal, then stand with your feet touching together, then stand with your feet as far away from each other as possible then try standing on one foot on one side of the scale.

My scale sucks ass. Standing on 1 foot is enough to completely throw the thing off.

 

[spidey07]

Draw a free body diagram. Gravity is still there, it's still constant and the only force is the spring in the scale.

You could weight yourself with a dozen scales if you wanted, the force would be the same.

 

[Leros]

No I think it would still work (if the free body diagram in my head is correct). As long as the scale can be relied upon to only measure vertical forces then the sum of the scales should be your weight. If the scale is mechanical in nature then the lateral forces probably add some friction to the system which would introduce inaccuracies.

I think you're right in theory, but scales seem to need a fairly even distribution of weight. If I put more weight on one side, I get an incorrect reading. So having lateral force would screw up the reading.

 

[rcpratt]

My scale sucks ass. Standing on 1 foot is enough to completely throw the thing off.

According to highly scientific tests just performed in my bathroom, this is true. Although I also have terrible balance.

Foot position didn't seem to matter.

 

[Possessed Freak]

So if you had a plane on two treadmills with built in scales....

Would ground effect cause the scales to read a higher value than the weight of the plane!?

 

[Jeff7]

Isn't that how some truck weigh stations work. They weigh each set of axles separately.

Or how the freight scale where I work operates. It's got 4 load cells, one under each corner. Each one deflects a bit under the force exerted by the freight. Combine it all, and you've got the total weight of the object.

Would ground effect cause the scales to read a higher value than the weight of the plane!?

Is one cold with solution?

You might also have to watch for anomalous effects caused by any alternators in the vicinity. They warp spacetime more than ordinary matter does.

 

[slayer202]

You would have to balance yourself well. If you weight was shifting, one scale might lock in a reading, while the other takes a reading at a difference point in time, where your weight is distributed differently. so while the combined weight will always be the same, that's only true if both readings are from the exact same time