estimates, averages, and sig figs october 6, 2015 (2.2 in your books)
TRANSCRIPT
Jonas Salk• Invented polio vaccine• 58000 people used to get
polio in the US each yearo 1/3 of them ended up
partially paralyzedo Iron lung
• Funded by March of Dimes
• Refused to patent invention
• Polio now gone in all but 3 countries
Percent Error• Another way to evaluate accuracy is with percent
error (% err, % E, PE)• In a good experiment, percent error is < 5%
• Sometimes you’ll see “theoretical” or “actual” instead of “true” – this is still OK
• The top half of the equation is often an absolute value I symbol |
RangeRange: the spread of data
Math: biggest # - smallest #
In high school/college you might have a different definition, but use this one for now.
8th grade
Anomalous Data• Sometimes you make a data set and one number
looks really weird• This is anomalous data• Anomalous data is useful – it can tell you if your
equipment isn’t working right, or maybe you forgot to control for a variable
• If your averages and percent error are strange, look for anomalous data
Significant Figures• Significant figures = sig figs• How scientists tell each other
how precise a number is.• Sig figs are made up of all the
measured values (increments) + one that we estimateo Like how we measured volume in a
beaker, then estimated in between the smallest marks
• From now on, all answers must be in sig figs!
Sig the Fig
Zeroes in Sig Figs• A number that isn’t zero always counts• Zeroes in the middle always count• Zeroes at the start don’t count• Zeroes at the end don’t count unless there’s a
decimalNumber Significant
Parts# Sig Figs
45357 45357 5
405 405 3
200 200 1
200.00 200.00 5
200.5 200.5 4
0.0045 0.0045 2
10. 10. 2
More Sig Figs!
Number Significant Parts # Sig Figs
2502757 2502757 7
14.058000 14.058000 8
0.000450 0.000450 3
10000 10000 1
67 67 2
0100 0100 1
2.000 2.000 4
2.00200 2.00200 6
3850 3850 3
Adding/Subtracting Sig Figs
• Use the smallest number of decimal places (or tens, hundreds, thousands, etc)
• Round to that number!
More Stuff• If you are using a conversion factor like “1000 g/
1 kg” you have unlimited sig figs
• If you are using a counting number like “2 people,” you have unlimited sig figs
Homework• Worksheet! It’s double-sided and due Friday.
• All answers must be in sig figs.
• Worksheet covers 2.1 and 2.2.