The Metric System (SI)

Common Metric Prefixes

Factor          Name Symbol

109 giga G

106 mega M

103 kilo k

10-1 deci d

10-2 centi c

10-3 milli m

10-6 micro µ

10-9 nano n

10-12 pico p

See http://online.cctt.org/physicslab/content/Phy1/lessonnotes/metricsystem/lessonSIsystem.asp

The Metric System (SI)SI fundamental units

Quantity Name Unit

length meter m

mass kilogram kg

time second s

electric current ampere A

temperature kelvin K

amount of substance   mole mol

luminous intensity candela cd

See http://online.cctt.org/physicslab/content/Phy1/lessonnotes/metricsystem/lessonSIsystem.asp

Significant Figures (or Digits)a.k.a. Sig Figs or Sig Digs

A figure or digit is significant if… it is a nonzero figure. (52 has 2 sig figs) it is a figure between nonzero figures. (502 has 3 sig figs) it is a zero to the right of a decimal point and following a nonzero figure. (52.00 has 4 sig figs) it is a zero to the right of a nonzero figure, but left of an understood decimal, ONLY if specifically indicated to be significant by a bar. (52000 has 3 sig figs)

A figure or digit is NOT significant if… it is a placeholder zero. to the right of a decimal point and to the left of a nonzero figure, i.e., PLACEHOLDER (0.00052 has 2 sig figs) to the right of nonzero figures with an understood decimal, i.e., PLACEHOLDER (5200 has 2 sig figs)

Rules for computations with significant figures…

• Analogy: A chain is only as strong as its weakest link.

Addition/Subtraction• Keep only the leftmost place of uncertain figures.

It becomes the rightmost in the answer. (52.1 + 3.61972 = 55.7)

Multiplication/Division• The number of significant figures in the answer

cannot exceed the number of significant figures in the least precise factor. (52 x 0.0387564 = 2.0)

Accuracy vs. Precision

Target Analogy

Precise, not accurate

Accurate, not precise

Both accurate & precise

Neither accurate, nor precise

Measuring Accuracy

Accuracy is the closeness of measurements to an accepted value

Absolute Error, Ea = |O-A|where O = observed valueand A = accepted value

Relative Error, Er = 100% (Ea / A)

Measuring Precision

Precision is the agreement among several measurements

Absolute Deviation, Da = |O-M|where O = observed valueand M = mean of measurements

Relative Deviation, Dr = 100% (Daavg / M)

Mass Densitya measure of how much matter

is packed in a given space

Density = mass / volume

On your own and before you get into your lab groups, come up with at least three questions about the accuracy and/or precision of density

determination that your group could investigate.

The table below gives the accepted value for the density of each material at

standard temperature and pressure. What is the specific gravity of each one?

Material Density Specific Gravity

brass 8.56 g/cm3

copper 8.96 kg/dm3

iron (steel) 7.88 kg/dm3

aluminum 2.70 g/cm3

nylon 1.16 g/cm3

acrylic 1.19 kg/dm3