From: paraluman (psticedurkin@punahou.edu)
Date: Thu Aug 31 2000 - 01:09:30 PDT
Message-ID: <001a01c01322$cb2095a0$6c8ba118@hawaii.rr.com> From: "paraluman" <psticedurkin@punahou.edu> Subject: Re: Pinhole Digest #450 - sig figs Date: Wed, 30 Aug 2000 22:09:30 -1000
One way to explain zeros in sig figs is to always convert to or think in
scientific notation. 0.003 g of something is the same thing as 3 x 10^-3 g
of something. The ^10-3 part just tells you the magnitude of the number,
while the first part tells you all you need to know about sig figs. If you
have 0.0030 g of something then you get 3.0 x 10^-3 instead- 2 sig figs.
Try this exercise for the adding and subtracting rule, which really seems to
get them. Have the students fill a bucket of water about 3/4 full. Have
them measure the water using the crude markings on the side and record to
the correct amount of sig figs. Then have them use a 10 mL graduated
cylinder or other small mL cylinder to add exactly 2.0 mL of water to the
bucket. How much water is now in the bucket to the correct number of sig
figs? Visually, there is hardly any change in the water level, so they see
that even though I know the 2.0 mL measurement to one decimal place, when I
get the new volume, I loose that accuracy. The bucket's crude markings did
not allow me to measure the original amount to the tenths place so according
to the rule, my answer is limited by the less accurate instrument (graduated
cylinder, bucket, scale, etc). I use the saying "It's a drop in the bucket"
to help them remember the addition rule logic (although some of them have
never heard of this saying, it does help)!
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