Wed 8 Mar 2006
Heavy-Handed
Posted by Erin under Daily Life
[8] Comments
So, there I am at work, waiting for my burrito to heat in the microwave, and the electronic mail scale nearby captures my attention. I ask myself: “How much does my hand weigh?” I put my hand on the scale. the numbers fluctuate so rapidly that I suspect I am putting more pressure on it than just gravity.
I hold my wrist and plop my hand back on the scale. It registers anywhere between .5 lb to 1.5 lb. I let go of my wrist and it goes up past 3 lb. I ask myself: “Am I weighing my whole arm?” But I’d expect my arm to weigh more than three pounds.
Problem: how can I accurately weigh my hand without cutting it off? A question for the ages. for the sages. for the microphages. Maybe not that last group, they just eat bad things and don’t care about my hand one way or the other.
I asked google how much a hand weighs and it came up with many other interesting questions: how much does guilt weigh? how much does the sky weigh? how much does a prayer weigh? How much does a paint job weigh? No answer to the original question.
A fascinating problem. I tried a simulation on my office desk but couldn’t figure anything out. Maybe one of your science-y friends can help you?
Where is Dr. Bromer when you need him? (Oh, yes, probably delivering triplets in distress . . . or setting up his laptop camera)
I think this must be possible with a lot of water, a very sensitive scale, and some math, but I can’t work it out.
If one assumes that one is as dense as water, then it’s easy: just figure out the volume of your hand using a graduated cylinder full of water and calculate the weight of that much water.
Since humans generally float, the hand may be less dense than water. Then again, the hand may be a relatively denser area of the body compared to fattier areas. Again, we run against the same issue: in order to discern the actual density of the hand, it would have to be cut off.
“Weigh” is one of those words where if you look at it too long, it ceases to have meaning.
I think Gary’s approximation is the most correct. Human’s float only because their lungs (and stomachs) are full of air. Since the body is composed of between 65 and 80% water, it would be a decent approximation.
Erin needs to rummage through her kitchen for a large metric measuring container, and measure the water line both pre and post-submerging. Subtract the difference, convert milliliters to grams, then divide by 2200, and that will provide a rough weight in pounds…
Then, there is the way that we obstetricians estimate fetal weight. We imagine how many 5 pound bags of sugar the baby composes. 1 1/2 bags = 7 1/2 pounds etc. My hand looks like about 1/4 of a bag of sugar, so I am going with about 1 1/4 pounds (567 grams). I’ll have to dunk it tomorrow to check.
Hmmm. A few math mistakes late at night – perhaps too many triplets. It’s divide by 454 not 2200. And, I am revising my guess to 1/6 a bag of sugar, or 378 grams.
O! The math! Thanks Jason. I like the electronic scale, is the thing. It has flashing red numbers that are mesmerizingly attractive. I also don’t have a graduated cylinder.
Aside to Rebecca: weighweighweighweigh down yonder in the paw paw patch.
The way I see it, the problem is that you can’t separate the different forces. 1. The force of gravity on the whole arm versus just the hand, and 2. the force of any additional pressure I might put on the scale, apart from gravity.
I say, 1. numb my upper body to get rid of problem of additional force. Then slowly lower the hand onto the scale (should be at shoulder level), using a rope-and-pulley system attached to the ceiling and my wrist. That way you would only be putting the weight of the hand, from the wrist down, onto the scale. anyway that’s what I came up with while waiting for a train. Naysayers? Do your worst!
Sheesh!
Get a fish scale and some diving weights so you’re not buoyant. Immerse yourself so that only your hand is out of water, and you are suspended off the bottom by the fish scale on your finger. Have somebody read your weight. Now have them lower the fish scale until your hand is also immersed. Read your weight again. The weight difference between your hand exposed and your hand submerged (an ounce or two) is the difference in density between your hand and water. Now climb out of the pool, stick your hand in a full water container, and capture the displaced water. Weigh the displaced water (not the container), subtract the ounce or two of measured density difference, and voila, the weight of a heavy hand. I like the estimate of about a pound.
Good one, Dad. I like all the accessories involved.
Erin