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 = m (oops) What should the “accepted value” be?

Practice Problem That’s right! m Error = accepted – experimental = – = m

Practice Problem % Error =  Error  x 100% Accepted =  m  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 m

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 numbers 1 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 = s 3 1 cm x 1cm x 1cm = 1cm 3 = 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