Chapter 7 Notes

1.    Dimensions vs Units:

·         A dimensions is a measurable extent. Height, length

·         A unit lets us to quantify a dimension.

·         Length is dimension, there are many units of length such as miles and feet.

2.    SI Prefixes:

·         Based on multiples of 10.

·         We avoid scientific notation or long strings of zeros.

·         Instead of: 198,000 We say: 198 Kilometers

3.    The 7 fundamental dimensions & base units:

·         Dimension: Length Symbol: L

·         Dimension: Mass Symbol: M

·         Dimension: Time Symbol: T

·         Dimension: Amount of Substance Symbol: N

·         Dimension: Light intensity Symbol: J

·         Dimension: Electric Current Symbol: I

·         Unit: Kilogram Symbol: kg

·         Unit: Meter Symbol: M

·         Unit: Second Symbol: s

·         Unit: Kelvin Symbol: K

·         Unit: Mole Symbol: mol

·         Unit: Candela Symbol: cd

·         Unit: Ampere Symbol: A

4.    Official SI rules:

·         If the unit abbreviation is a capital letter, it’s named after a person.

·         Symbols of units are not plural (cm, not cms.)

·         You do not put a period after the symbol unless at the end of a sentence.

·         Symbols are written like (m, k, L) not (m, k, l)

·         One space separates the number and symbol.

·         Spaces or commas may be used to group digits by threes.

·         Symbols with multiple units are joined with a space or interpunct.

·         Do not combine prefixes to form compound prefixes. Correct; picojoules (pJ) Incorrect; kiloMegaseconds (kMs)

5.    Difference in SI, AES and USCS. What are they? Which do you prefer? Why?:

·         SI: System International (meters, kilograms, seconds, kelvin, celcius)

·         AES: American Engineering System (feet, pounds, seconds, Fahrenheit, rankine)

·         USCS: United States Customary System (feet, slug, second, Fahrenheit, rankine)

·         I prefer to use AES and USCS only because I am used to the units and I have used them before.

6.    Unit Conversion Procedure:

·         This was a difficult topic to understand. However, the procedure is as follows.

·         Write the value and unit to be converted.

·         Write the conversion formula between the given unit and the desired unit.

·         Make a fraction, equal to 1, of the conversion formula in Step 2, such that the original unit in step 1 is located either in the denominator or in the numerator.

·         Multiply the term from step 1 by the fraction developed in step 3.

·         Cancel units, perform mathematical calculations, and express the answer in reasonable terms.

7.    Unit Conversion Procedure involving multiple steps:

Refer to table 7-4 to 7-8 in Thinking like an Engineer. Page 161