CHAPTER2

CHAPTER 2: SCIENTIFIC MEASUREMENT
Lecture

2.1 The Importance of Measurement

1. Qualitative measurements give results in a descriptive nonnumeric form.

2. Quantitative measurements give results in definite form, usually as numbers.

2.2 Accuracy and Precision

1. Scientists want to make "good" measurements.

2. Accuracy is how close a single measurement comes to the actual dimension of true value of whatever is measured.

3. Precision is how close several measurements are to the same value.

4. See concept practice 3. Page 30.

2.3 Scientific Notation

1. In scientific notation a number is written as the product of two numbers: a coefficient and a power of 10.

2. Multiplication: multiply coefficients, add exponents.

3. Division: divide coefficients, subtract exponents.

4. Addition and subtraction: make exponents the same.

2.4 Significant Figures in Measurements.

1. Significant figures in a measurement include all the digits that are known precisely plus one last digit that is estimated.

2. Rules of significant figures:

Every nonzero digit insignificant.
Zeros between nonzeros are significant.
Zeros in front of nonzeros digits are not significant.
Zeros at the end of a number AND to the right of the decimal point are significant.
Zeros at the end of a measurement and to the left of the decimal point are not significant if just place marker. 300 m, 7000 m, and 27210 m are not significant. (1, 1, and 4 digits). Use scientific notation to show that these zeros are really MEASURED.
Infinite significant figures - two instances. First = counting. Second = exactly defined quantities (conversions in a system of measurement). 1 hr = 60 min. 100 cm = 1m.

2.5 Significant Figures in Calculations

1. An answer cannot be more precise than the least precis measurement from which it was calculated.

2. Examples of x, /, +, -

2.6 The International System of Units, SI

1. Always use CORRECT UNITS. ALWAYS SHOW UNITS.

2. Need a reference standard. Internationals System of Units was established in France in 1790. Revised and adopted in 1960.

3. Seven SI base units - Table 2.1

4. Also know metric units in table 2.2, 2.3 , and prefixes in 2.4

2.7 Units of Length

1. Meter is basic SI unit of length.

2.8 Units of Volume

1. Volume is space occupied by any sample of matter - Liter=1000ml=1000cm3 (cube 10cm x 10cm x 10cm)=1dm3.

2.9 Units of Mass

1. Weight is a force. Depends on gravity. Can change with location (moon = 1/6 gravity)

2. Mass is amount of matter in object.

3. 1 kilogram (kg) is basic SI unit of mass. It is mass of 1 liter of water at 4^oC.

4. Gram is 1/1000 of kg. It is mass of 1 cm3 (ml) water at 4oC.
2.10 Measuring Density
1. Density is the ratio of the mass of an object to its volume.

Density=

Mass Volume

2. See Table 2.8, page 46 for examples.
2.11 Specific Gravity
1. Specific gravity is a comparison of the density of a substance to the densiy of a reference substance, usually at the same temperature - usually water at ^oC.

Specific Gravity =

Density of substance (g/cm³)
density of water (g/cm³)

2. The specific gravity of a liquid can be measured with a hydrometer.
2.12 Measuring Temperature
1. Temperature is the degree of hotness or coldness of an object.
2. Most objects (except water) expand when heated and contract when cooled.
3. This is principal behing thermometer.
4. Celsius scale: 0oC is freezing; 100oC is boiling of water.
5. Kelvin (SI); Freezing of water is 273 K and boiling is 373 K.
6. Zero on the Kelvin scale is -273oC.

K = oC + 273 or

oC = K-273

Change in 1o in one is change in 1o in the other.