Scientific Measurement

Chapter 3

3-1 The Importance of Measurement

• Qualitative vs Quantitative Measurement

•What color vs What mass?• Scientific Notation

•Powers of Ten

3-2 Uncertainty in Measurements• Accuracy, Precision and

Error

• Communicate the quality of Experimental Data and Calculations

3-2 Uncertainty in Measurements

• Accuracy

•How close to the accepted value is the measurement?

3-2 Uncertainty in Measurements

• Precision

•How are the Data Grouped?

–Tight vs Loose

3-2 Uncertainty in Measurements

• Error = Accepted value – Experimental

value• % Error = Error x 100%

Accepted value

Practice Problem

• Suppose you compare a wooden meter stick to a certified standard meter stick and get the following data:

Practice Problem

• Length of wooden meter stick

= 1.009 m (oops)

• What should the “accepted value” be?

Practice Problem

• That’s right! 1.000 m• Error = accepted –

experimental = 1.000 – 1.009 = -0.009 m

Practice Problem

• % Error = Error x 100%

Accepted

= -0.009m x 100%

1.000m

= 0.9 %

Significant Figures in Measurements

• How well do you know your data? Is it -

•0.8m•0.75m•0.753m•0.7529m

Significant Figures

• All four measurements could have come from the same object measured with increasingly precise equipment.

•“Degree of Precision”

Significant Figures

• Significant Figures show all digits directly obtained in a measurement plus the first estimated digit.

Significant Figures

• The number of significant figures in measurements is governed by RULES See pages 56 & 57… beware the lowly zero, it will confuse you.

Significant Figures

• Exact numbers: infinite sig figs• counting numbers1 cookie, 2 cookies …• defined quantities

1 meter = 100 centimeters

Significant Figures in Calculations

• It’s a different game.

• You can’t know a calculated result any more precisely than your least precise term.

• “Weakest Link”

Significant Figures in Calculations

• Rules governing addition/subtraction are –DIFFERENT – from the rules governing multiplication/division.

–See pages 58-61

3-3: Units

• SI = International System of Units

– see Table 3.1 page 63

• Base units vs derived units.

Units

• SI is related to the metric system.

• We generally use the metric system and its prefixes.

–See Table 3.2 page 64

Units: Length

• Meter

• Derived units:•Area (squared)•Volume (cubed)

Units: Volume

• Space matter occupies• Unit cubes• V= lwh = s3

• 1 cm x 1cm x 1cm = 1cm3 = 1ml

• 1 liter = 1,000 ml

Units: Mass

• Amount of matter in object

• Unaffected by gravity

• 1 ml water = 1 gram

Units: Density

• Relates mass of an object to its volume

• Property of all matter• Density = mass = m

– volume v

Units: Temperature

• SI: Kelvin scale (absolute)•unit = K (kelvin)

• Metric: Celsius•unit = C (degree Celsius)

• Pet peeve: There is no such thing as a “Degree Kelvin”

Units: Temperature

• Convert from K to C C = K – 273

• Convert C to K

•K = C + 273