Systeme International d’Unites The units and measurement of science

SI Units Modern form (1960) of metric system Uses 7 base units from which all other units can be derived from. Length (meter – m) Mass (kilogram – kg) Time (seconds – s) Electric current (Ampere – A) Temperature (Kelvin – K) Quantity of matter (mole – mol) Luminous intensity (candela- cd)

SI Prefixes – getting smaller or larger Kilo hecto deka base deci centi milli km hm dam meter dm cm mm 1000 100 10 1 0.1 0.01 0.001 Whenever you move from one unit to another you only need to multiply or divide by 10.

SI Prefixes – getting smaller or larger 1 km = 1000 m 1 kL = 1000 L 1 hm = 100 m 1 hL = 100 L 1 dam = 10 m 1 daL = 10 L 1 dm = 0.1 m 1 dL = 0.1 L 1 cm = 0.01 m 1 cL = 0.01 L 1 mm = 0.001 m 1 mL = 0.001 L 1000 mL = 1000 cm3 = 1 L

Advantages of SI Units Universal – with the exception of a few countries (US is an exception). A common language for science. Based on 10. The numbers will never change, only the decimal place will change.

Why doesn’t U.S. use SI Units Metric Conversion Act of 1975 Omnibus Trade and Competitiveness Act of 1988 Expensive to switch over. Not using metric caused the Mars Climate Orbiter to burn up instead of orbit Mars. The military uses metric extensively.

Standard Units Based on imperial units. What we are used to. Foot, Inch, Mile, Pound. Link, Acre, Rod, Dram, Gill, Beer Barrel, Oil Barrel, Hogshead, Peck. Numbers and conversions between units are all different – nothing unifying.

Standard Units & Metric Units 1 meter = 3.28 feet 1 inch = 2.54 centimeters 1 fl. oz. = 29.6 milliliters (mL) 1 kilogram (kg) = 2.2 pounds (lbs) 1 pound (lbs) = 454 grams (g) 1 mile = 1.6 km

Bodily Measurements The width of your thumb = 1 inch The width of your pinky nail = 1 cm The volume of the tip of your pinky = 1 cm3 or 1 mL Your wingspan = your height Elbow to wrist = the size of your foot “Hang Loose” = the size of your foot

Measurement - Length Always measure as accurately as possible Measure to one place past the smallest scale of measure. The scale is 0.1 – you are allowed one place smaller – 0.01 The scale is 1 – you are allowed 0.1

Measurement - Length What would you write down for the measurement? Ruler A? Ruler B? Remember, the last number is an estimate 4.8 ? 4.85 ?

Measurement - Length 9.60 3.20 cm 2.34 cm

Measurement - Volume Water curves because of surface tension and gravity Forms a meniscus Always measure the bottom of the meniscus at a level sight line

Measurement - Volume Same rules apply in terms of what needs to be reported What volume should you report? 43.0 mL

Measurement - Volume 3.15 2.95 4.10 1.09 8.67 5.45

Data Terms Quantitative Measurements Examples Give results in a definite form, usually values 24L, 10 cm, 14 ºC

Data Terms Qualitative Measurements Examples Give results in a descriptive, non-numeric form. The beaker was warm. The density was greater than that of water.

Data Terms Accuracy Examples How close a measurement comes to the actual value of whatever is being measured Water freezes at 0º C, and boils at 100º C. How close is the measurement to the values.

Data Terms Precision Examples Reproducibility of the measurement 9 out of 10 lab groups report the temperature of boiling water to be 95º C. A basketball player shoots 20 free throws, 18 of which bounce off the right side of the rim.

Accuracy vs. Precision Target Practice Accurate Precise Accurate & Precise