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The Nature of Science & Measurement

A.  What is science?

1.  Science is the total collection of knowledge gained by man's observation of the physical universe.
2.  It tries to answer the questions "how" and "why."
3.  It is a logical way of problem solving.
B.  Two main types of science
1. Pure science - studying things for the sake of gaining knowledge; new discoveries.
2. Applied science - the use of pure science in practical ways (technology).
C.  Physical Science
1.  Physical science is an introductory study of chemistry and physics.
2.  Chemistry is the study of matter and changes its undergoes.
3.  Physics is the study of energy and motion.
D. Limitations of Science
1. Cannot make value judgments.
2. Cannot prove something doesn't exist (universal negative).
3. Scientific investigation is as limited as the instruments we use.
E. Scientific Statements
1. Facts - things that are observable and indisputable.
2. Data - any piece of information; usually gained through experimentation.
3. Laws - statements that describe patterns in nature with no known exceptions.
4. Theories - explanations usually based on evidence (may be wrong).
5. Models - man-made ideas to help us visualize scientific concepts.
F. The Scientific Method
1. A logical approach to problem solving.
2. Steps:
a. Identify the problem to be solved (usually in the form of a question).
b. Gather information (research).
c. Make a hypothesis (educated guess).
d. Experiment to test the hypothesis.
e. Analyze data from the experiment and draw conclusions.
f. Make predictions.
G. Scientific Experimentation
1. An experiment is a controlled test to find the answer to a question.
2. Only one condition in an experiment is changed at a time.
a. The conditions that affect the outcome are called variables.
b. Manipulated (independent) variable - the one changed by the experimenter.
c. Responding (dependent) variable - the condition that changes because of the manipulated variable.
3. Factors in experiments that do not change are called constants.
4. Experiments have two parts:
a. Control group - group under normal conditions (nothing unusual done to it).
b. Experimental group - the test group in which variables are changed.
5. Good observational skills are important (this includes being able to measure accurately).
6. The goal of an experiment is to predict what might happen in similar situations.
H.  SI - The International System of Units is the accepted system used worldwide by scientists
1.  Based on multiples of 10
2.  Common prefixes:
          a.  mega- (M-) 1 000 000x
b.  kilo- (k-) 1 000x
c.  hecto- (h-) 100x
d.  deka- (da-) 10x
e.  deci- (d-) 0.1x (1/10)
f.  centi- (c-) 0.01x (1/100)
g.  milli- (m-) 0.001x (1/1 000)
h.  micro- (u-) 0.000 001x (1/1 000 000)
I.  Common types of measurements
1.  Length - the distance from one point to another.
a.  Base unit is the meter (m)
b.  Tool is the metric ruler
2.  Volume - the amount of space an object takes up.
a.  Base unit is the liter (l or L)
b.  Tools:
1)  Metric ruler for regular solids
2)  Graduated cylinder for liquids
3.  Mass - the amount of matter in an object.
a.  Base unit is the gram (g) [SI base unit is the kilogram (kg)]
b.  Tool is the balance or scale
4.  Weight - a measure of gravitational force.
a.  Base unit is the newton (N) (1kg mass has a weight of 9.8 N)
b.  Tool is the scale
5.  Time - how long an event takes to happen.
a.  Unit is the second (s)
b.  Tool is the clock
6.  Temperature - the amount of kinetic energy an object has.
a.  SI unit is the Kelvin
b.  Commonly used unit is the degree Celsius (C)
c.  Tool is the thermometer
7.  Density - how compacted the mass is in a substance.
a.  Units are g/mL, g/cm^3, or kg/m^3
b.  Found by: D = mass / volume
c.  Objects float if their density is less than the density of the liquid they are in
J.  Accuracy, Precision, and Error
1.  Precision is how close several measurements are to each other.  It may also be the degree to which a measuring instrument is capable of measuring.
2.  Accuracy is how close a measurement is to the accepted value.
3.  How to find the amount of error (expressed as a percent):
Difference between the Average of Trials and the Accepted Value
--------------------------------------------------------------- X 100% = % Error
                         Accepted Value
K.  Significant Figures
1.  Used only for measured quantities.
2.  Any measurement should have a number of significant digits equal to the reading of the instrument plus one uncertain digit.
3.  How to count the significant figures in any number:
a.  All non-zero digits are significant (ex. 14.232 has 5 sig. dig.)
b.  Leading zeros are not significant (ex. 0.00045 has 2 sig. dig.)
c.  Confined zeros are significant (ex. 6007 has 4 sig. dig.)
d.  Trailing zeros are significant only if there is a decimal point in the number or if they have overbars
ex. 36,000 has 2 sig. dig.
ex. 36,000.0 has 6 sig. dig.
4.  Addition or subtraction - the answer's last place value should be the same as the first doubtful place value in the problem.
   ex.  25.657
         1.31
      + 13.2
      --------
        40.167 (calculator answer)
        40.2   (correct answer)

5.  Multiplication or division - the answer should have a number of significant digits equal to the part of the problem that has the fewest significant digits.
   ex.  6.038 x 2.57 = 15.51766 (calculator answer)
                     = 15.5     (correct answer)

6.  Rounding Off
a.  If the first digit to be dropped is less than 5, that digit and all digits that follow it are simply dropped
b.  If the first digit to be dropped is greater than 5, or a 5 followed by any non-zero digits, all are dropped and the last digit to be retained is increased in value by one.
c.  If the first digit to be dropped is 5 and it is not followed by by any non-zero digit, the odd-even rule applies.
    The odd-even rule says to drop the 5 and any zeros that follow it and then either
1)  round up to 6 if the digit before the 5 is odd, or
2)  leave the last digit at 5 if the digit before the 5 is even.
ex.  62.650 rounded to 3 significant figures becomes 62.6
ex.  62.350 rounded to 3 significant figures becomes 62.4
L.  Scientific Notation (students should already know this)

 
M.  Special Techniques
1.  Water displacement method
a.  Used to measure the volume of an irregularly shaped object
b.  Place a known amount of water in a container
c.  Submerge the object
d.  Measure how much the water rose
2.  Using a meterstick
a.  Place stick on its edge to measure
b.  Always start at 1cm and then subtract 1cm from final number
3. Using a graduated cylinder
a.  Keep at least 10cm (handsbreadth) from the edge of the tabletop
b.  Sight the meniscus (the curve)
N. Brief History of the Metric System
The metric system is a system for measuring things. Scientists around the world use the metric system for their measurements. The worldwide system is known as the International System of Units (SI). The metric system was invented by French scientists in the 1700's. It bases all measurements on units of the number ten. This makes it easy to convert between different units of measurement. The United States passed a law many years ago to officially adopt the metric system. The U.S. is the only major nation in the world today that does not use the metric system in everyday life.