1. Measurement and uncertainties
Ch. 2 Sect. 2
Measurement and uncertainties

2. Precision and Accuracy
Describes degree of exactness of a measurement
Which is more precise
Measurement A = 18.8 [+/-] 0.3 cm
Measurement B = 19.0 [+/-] 0.2 cm
Measurement C = 18.3 [+/-] 0.1 cm
Measurement C is more precise

3. Precision and Accuracy
Describes how well results of an experiment agree with standard value
If block from previous data was 19.0 cm, which measurement was most/least accurate?
Measurement B was most accurate
Measurement C was less accurate

4. Techniques of taking measurements
Make sure that your angle when taking a measurement is correct
Volume of a liquid 
Length on a meter-stick 
Parallax
Apparent shift in position of an object when veiwed at different angles

5. Significant Digits/Figures
Valid digits in a measurement

6. Measurement Object A Ruler 1- 6.80 cm Ruler 2 – 6.8 cm
The “0” is the estimate or uncertain digit
There are 3 sig figs in this measurement
Ruler 2 – 6.8 cm
The “8” is your uncertain digit
There are only 2 sig figs
Which is more precise?
Ruler 1

7. Which Zero’s are significant?
If you answered measurement “ m” you would still only have 3 sig figs
First two zeros only locate the decimal (place holders) and aren’t significant
The last zero is the estimated digit m
6 is the estimated digit while 0’s locate decimal
3 sig figs
km??
6 sig figs

8. Rules for Sig Figs 1) Non zero digits are always significant
2) All final zeros after the decimal point are significant
3) Zeros between two other sig digits are significant
4) Zeros that are used as place holders are not significant

9. Practice Problems 2804 m 2.84 km 0.0029 m 0.003068 m 4.6 x 105 mkg
x 107 km

10. Practice Problems 2804 m  4 2.84 km  3 0.0029 m  2 0.003068 m  4
4.6 x 105 m  2
4.06 x 10-5 m  3
75.00 m  4
kg  4
x 107 km  5

11. Add and Subtract with sig figs
Important to remember that the result can never be more precise than the least precise measurement
When (+) or (-), first perform the operation then round to the least precise value m
2.343 m
+3.21 m
=  m

12. Multiply or divide
After (x) or (/) calculation, note the factor with least number of sig figs and round product or quotient to that number of digits
3.22 cm x 2.1 cm
=  6.8 cm2