Measurement Chapter 4

Scientific study, like cooking, relies on definite measurements. The very word science implies exactness. To obtain meaningful experimental results and to develop a procedure that can be duplicated, measurements must be both precise and accurate.

Accuracy and Precision Accuracy – (voc. term) Two separate concepts. Vital to successful measuring. Ex. If you need 10 grams of salt, and the amount that you scale registered is 10 grams, then the measurement is considered accurate.

Precision – (voc. Term) Need more than one measurement Compare the results.

The Metric System A common language used all around the world for measurement. – Beverages are sold by the liter – Food labels indicate the mass in grams Your car has both miles and kilometers

Metric Units Unit of measure is needed – English system - unit measuring length = inches – Metric system - unit measuring length = meter (m) – Gram (g) to measure mass – Liter (L) to measure volume

Metric Prefixes Decimal system (voc term) The metric system is based on the decimal system = numbers are expressed in units of ten.

(Metric Prefixes con’t) Prefixes – used to indicate – Multiple or fraction of the base unit – Can be combined with any unit of measure

Can use kilometers to describe a large number of meters. Prefixes Kilo = meters = 1kilometer grams = 1 kilogram liters = 1 kiloliter

Measurements smaller than 1 meter Prefixes – -Milli -Centi -Deci Describe fractions of a meter

PrefixMeaningNumerical Value Unit ExampleRelationship to Unit Kilo (k)Thousand1000Kilometer (km)1 km = 1000 Deci (d) Centi © Mili (m) Tenth Hundredth Thousandth Decimeter (dm) Centimeter (cm) Millimeter (mm) 10 dm = 1 m 100cm = 1m 1000mm = 1m Metric Prefixes (chart on page 63)

Metric Unit SymbolMeasurement VisualizationsEnglish Equivalent Gram Kilogram g kg A little heavier than a paper clip Almost nine sticks of butter oz 2.2 lb Meter Kilometer Decimeter Centimeter millimeter m km dm cm mm From the floor to about the doorknob About two-thirds of a mile About the diameter of an average grapefruit Length of a staple Width of a dime 1.09 yards 0.62 miles 3.94 inches 0.39 inches inches Liter militer L mL Just over a quart of milk A little less than ¼ teaspoon quarts 0.03 fluid oz Comparing Systems (Comparison Chart)

Recording Metric Data Estimating Measure correctly Report findings precisely and accurately

(Estimating con’t) Scales on laboratory measuring devices vary Ex: Beaker – markings every 10 mL of volume Graduated cylinder - marked to the milliliter

As you use the scales on laboratory equipment, make it a habit to estimate to one decimal place past the unit of measure marked on the scale. Ex. suppose you’re using a 100-ml graduated cylinder marked to whole milliliters, and the bottom of the meniscus is between 24 and 25 mL. You would report this as 24.3 mL or mL, depending on how far above 24 mL the volume is. Anyone who reads the data table will know that the last digit is just an estimate, but it will tell them whether the volume was closer to 24 mL or 25 mL.

Recording Final Zeros the bottom of the meniscus is exactly on the 24-mL line write 24.0 mL, it is clear that the volume is exactly 24 mL. by recording the final zero, you report your data more precisely.

Measuring in Metric Measuring length Use a metric ruler or meter stick Millimeters – smallest divisions on these tools – 10 mm = 1 cm – Each mm line = 1/10 of a centimeter

Measuring Length con’t

Measuring Volume Each container marked with a different scale Resulting in varying degrees of accuracy

Measuring Mass Metric Conversions Use of an electronic balance Converting English to metric and vice versa.

The Celsius Temperature Scale Fahrenheit scale Invented in the early 1700s by a German physicist, Gabriel Fahrenheit. Thermometer more accurate by using mercury instead of alcohol.

Celsius Scale Named for Anders Celsius, Swedish astronomer, developed in Formerly called the centigrade scale, means divided into 100 parts.

●100° separate freezing and boiling points on the Celsius scale ● Fahrenheit scale, the difference is 180 ° ●Celsius degree represents almost twice the temperature changes as a Fahrenheit degree.