SI System of Units

Chapter 13

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13.1 Background

SI System of Units = “metric system”Used worldwide except in US, Liberia, Burma

Old UnitsBushel = 8 GallonsStone =14 poundsCubit = Length of the Pharaoh’s elbow to fingertipHand = 4 inchesFortnight = 2 weeks

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History of the Meter?

Delambra and Mechain1792 to 1799“quadrant of meridian”Pole to Equator of Earth -> 10 million partsScratches on Platinum BarResurvey…10,002,288.3 meters

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SI Units

MKSmeters, kilograms, seconds

CGScentimeters, grams, seconds

Miles?1 mile = 5280 ft1 nautical mile = 1852 m

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Exercise

Give the MKS and CGS units for the following:

1. Volume2. Acceleration3. Density4. Force5. Energy6. Speed7. Orbital Period8. Frequency 9. Angular Velocity

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Multiples and Prefixes

1012

109

106

103

10-3

10-6

10-9

10-12

tera (T)giga (G)mega (M)kilo (k)milli (m)micro ()nano (n)pico (p)

Prefix Rule

Use a prefix that will give you 1, 2, or 3 digits to the left of the decimal.

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ExerciseUse the “prefix rule” to rewrite each measurement

1. 485,684 m2. 0.075 g3. 3.21 × 105 Hz4. 3.21 × 108 Hz5. 3.21 × 10-10 A6. 7,300,000 V7. 0.000000635 m/s

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ExerciseRound the following numbers to three significant figures.

1. 485,684.0012. 0.07548343. 0.039999994. 3.56485. 7309996. 600,001

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ExerciseWrite each of the following in scientific notation.

1. (0.0134 m)/(558 sec)2. (248287in2)(1ft/12 in) 2

3. (452 m)(12000 N)4. (1,000,000 cycles)/(153 seconds)5. (2 radians)/(6.02 seconds)

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Problems 13.1 and 13.2

13.1 (a) 18.3 Newton(b) 45.6 n(c) 29.0 meter(d) 56.9 meter/sec(e) five m(f) 23 m/second(g) 493°K(h) 89.6m(i) 68.5 Kg(j) 98.4 m/s/s(k) 10 m’s(l) Mm/ms

13.1 (a) 18.3 N(b) 45.6 N(c) 29.0 m(d) 56.9 m/s(e) 5 m(f) 23 m/s(g) 493 K(h) 89.6 m(i) 68.5 kg(j) 98.4 m/s2

(k) 10 m·s(l) 1000 m/s

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Problems 13.1 and 13.2

13.2 (a) 9.8 x 105 m(b) 9.56 x 1010 J(c) 0.000056 s(d) 1,984,000 m3

(e) 35.6 x 10-4 g(f) 92.4 x 107 N

13.2 (a) 980 km(b) 95.6 GJ(c) 56 s(d) 1.984 Mm3

(e) 3.56 mg(f) 924 MN

Unit Jeopardy

SPS

Jet Propulsion Laboratory, Pasadena, CA

RELEASE 99-113

MARS CLIMATE ORBITER TEAM FINDS LIKELY CAUSE OF LOSS

“A failure to recognize and correct an error in a transfer of information between the Mars Climate Orbiter spacecraft team in Colorado and the mission navigation team in California led to the loss of the spacecraft, preliminary findings by NASA's Jet Propulsion Laboratory internal peer review indicate.”

“The peer review preliminary findings indicate that one team used English units (e.g., inches, feet and pounds) while the other used metric units for a key spacecraft operation. This information was critical to the maneuvers required to place the spacecraft in the proper Mars orbit.” Uh oh…