Calibration vs. Precision

1
Calibration vs. Precision

• If a balance is accurate, it should read 0 when
  nothing is on it.
• The process for making sure a balance or any
  equipment is accurate is called CALIBRATION.
• Clocks can measure to the minute, second or
  fraction of a second.
• This refers to an instruments PRECISION.

2
Need for Sig Figs

• Measurements must reflect the precision of the
  instrument used, so significant figures become
  important.
• When measuring, you record all known digits plus
  you estimate the final digit if possible.
• For example if your ruler measures to the nearest
  cm, you would estimate how far it is between the
  2 cm markings.

3
Rules for counting sig figs

• All nonzero numbers ARE significant
• Ex 234.5 4 sig figs
• All zeros between nonzero numbers ARE significant
• Ex 2304.5 5 sig figs

4
Rules for counting sig figs

• 3. Zeros that act as placeholders ARE NOT
  significant. Think of how youd rewrite these
  numbers as a fraction or in scientific notation
  the zeros would disappear.
• This includes any zeros left of nonzero digits
  or any number ending in zero that does NOT
  include a decimal.
• Ex 0.0234 3 sig figs
• 14320 4 sig figs

5
Rules for counting sig figs

• 4. All final zeros to the right of the decimal
  are significant.
• Ex 23.00 4 sig figs
• 5. Counting numbers and defined constants have an
  infinite number of sig figs.
• Ex 6 molecules, 60 seconds in a minute or 100

6
Try It

• Round each figure to 3 sig figs
• 219034
• 25.38
• 0.08763
• 119.99

7
Solutions

• Round each figure to 3 sig figs
• 219034 219,000
• 25.38 25.4
• 0.08763 0.0876
• 119.99 120.

8
Counting Sig Figs when adding/subtracting

• Your final answer must have the same number of
  sig figs to the right of the decimal as the
  starting value with the fewest digits to the
  right of the decimal.
• Ex 2.54 3.1 2.275 7.915 BUT your final
  answer needs to round to 7.9

9
Counting Sig Figs when multiplying/dividing

• Your final answer must have the same number of
  sig figs as the starting value with the fewest
  significant figures.
• Ex A box measures 2.5 on a side, so you find
  the volume to be 15.625 BUT you must round your
  answer to 16 cm3 since you only had 2 sig figs in
  your measurement.

10
Try It

• Complete the following problems, rounding answers
  to the correct number of sig figs
• (5.53 x 10-6 km) x (7.64 x 103 km)
• (9.33 x 104 mm) / (3.0 x 102 mm)
• (4.42 x 10-3kg) (2.0 x 102 kg)

11
Solutions

• Complete the following problems, rounding answers
  to the correct number of sig figs
• (5.53 x 10-6 km) x (7.64 x 103 km)
• 4.22 x 10-2 km
• (9.33 x 104 mm) / (3.0 x 102 mm)
• 3.1 x 102
• (4.42 x 10-3kg) (2.0 x 102 kg)
• -2.0 x 102

12
Try It

• The accepted length of a steel pipe is 5.5 m.
  Calculate the percent error and round to the
  correct number of sig figs for these
  measurements
• 5.7 m
• 5.1 m

13
Try It

• The accepted length of a steel pipe is 5.5 m.
  Calculate the percent error and round to the
  correct number of sig figs for these
  measurements
• 5.7 m .2/5.5 x 100 3.6
• 5.1 m -.4/5.5 x 100 -7.3