Tenzin's grandmother sieves wheat flour before making rotis, and flakes of bran stay behind in the…
Tenzin's grandmother sieves wheat flour before making rotis, and flakes of bran stay behind in the sieve. Tenzin says the sieve separates things by size — anything bigger than the holes stays back. His friend Yamini says it separates them by weight — heavy bits stay back and light bits fall through. Whose explanation is correct?
Who do you think is right? Pick one.
The answer: Tenzin is right, a sieve separates by size
Why
Yamini's idea sounds reasonable because in winnowing, weight really does matter — so it's natural to think every separation works that way. But look at what actually stays in the sieve: flakes of bran, which are among the lightest things in the flour. If weight decided it, they would have been the first to fall through. They stay back because they are bigger than the holes, while the fine flour particles are smaller and slip through. Each method uses one particular difference: winnowing uses weight (with the help of wind), sieving uses size. Test: in a separate bowl, mix a pinch of fine sand — much heavier than bran — with a few bran flakes and shake them through the sieve; the tiny sand grains pass straight through, while the big, light bran flakes stay behind. Tenzin is right: a sieve separates particles by their size compared with the holes, not by their weight.
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