A baffling physics question

by FatFreek 2005 25 Replies latest social current

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  FatFreek 2005

  For several weeks I've been treating myself to a hot chocolate milk (well, soymilk) before bedtime. Some 16 oz soymilk which I heat on high in our microwave oven. This is just enough time where the liquid begins to bubble along the top edge.
  

  I then take it out of the microwave and place it on my kitchen gram scale, stir it good enough to redistribute the heat, then reset the scale to zero grams.
  

  Next, I squeeze in the Hershey's Sytup, "Special Dark Mildly Sweet Chocolate" (fat free) into the warmed soymilk till the scale reads some 30 grams. (That's slightly more than 1 ounce for those of you more comfortable with ounces)
  

  And this is where it gets interesting. I stir that luke-warmed mix till the color is uniform and ready for the 2nd heating -- then read the scale. The 30 grams has now dropped to 29 grams.
  

  I put the mix back into microwave and punch the 30 seconds button, take it out and place it on the scale and stir again to even out the heat. Yikes! The scale now reads 27 grams.
  

  Back into the microwave and punch the 30 seconds button. This is the final heat so I take it out, place it on the scale and stir. The scale now reads either 27 grams or 26 grams.
  

  That's a 10 to 13 percent weight reduction -- and to this physics novice, a total mystery.
  

  Any thoughts -- while I relax and sip on my yummy treat?
  

  Len
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  Village Idiot

  I don't know if soymilk has water but it seems that something is evaporating with each microwaving.

  Maybe this guy knows.

  
  
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  FatFreek 2005

  Yes, soymilk is mostly water and what you say makes sense. While the only time that bubbles appear is before the first weight measurement, the two subsequent heatings raise the temperature considerably.
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  FatFreek 2005

  No doubt in my mind that he knows. If I only had his email address ....
• 

  waton

  try to replicate it with another scale. 0ne using actual weights & balance.
• 

  Scully

  How much of the liquid adheres to the spoon (via surface tension) whenever you stir it?

  To know that, you'd have to weigh the spoon after stirring your beverage to see if it has gained weight.
  
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  bohm

  It is possible a small amount of milk gets lost on the spoon + boiling but I am not sure that can account for the full effect. I think what you are experiencing is that the scale is slightly broken such that it change measurement after being pressed/depressed.

  Try this:

  After you have applied Syrup to the milk and stirred (scale reads 30 grams), remove cup and place an empty cup on the scale (the calibration cup). Fill the empty cup with cold water till it reads 30 grams again. Interexchange the two cups a couple of times and ensure the scale reads 30 grams every time.

  Place the calibration cup on the counter and repeat the experiment while ensuring the calibration cup reads 30 grams every time. If at the end of the experiment your microwaved cup reads 26 grams, and the calibration is 30, something is up!
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  FatFreek 2005

  To help put this in perspective, a penny (since 1982) weighs 2.5 grams -- so we're talking about the weight of one of those, plus some.
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  Listener

  place it on the scale and stir.

  
  

  From my experience with scales, if you stir food when it is sitting on the scale it will mess up the reading.
  
  
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  nelim

  16 oz would be what...? Half a kilogram? So in the end you lose less than 1% of your total drink right? That doesn't seem strange.