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
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