Voc. Terms Accuracy Decimal system Metric system Precision Chapter 4 Voc. Terms Accuracy Decimal system Metric system Precision

Measurement Chapter 4

Scientific study, like cooking, relies on definite measurements 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 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 – Need more than one measurement Compare the results.

A common language used all around the world for measurement. 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

Unit of measure is needed 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

The metric system is based on the decimal system. Metric Prefixes The metric system is based on the decimal system. 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 = 1000 -1000 meters = 1kilometer -1000 grams = 1 kilogram -1000 liters = 1 kiloliter

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

Metric Prefixes (chart on page 63) Meaning Numerical Value Unit Example Relationship to Unit Kilo (k) Thousand 1000 Kilometer (km) 1 km = 1000 Deci (d) Centi © Mili (m) Tenth Hundredth Thousandth 0.1 0.01 0.001 Decimeter (dm) Centimeter (cm) Millimeter (mm) 10 dm = 1 m 100cm = 1m 1000mm = 1m

Measurement Visualizations Comparing Systems (Comparison Chart) Metric Unit Symbol Measurement Visualizations English Equivalent Gram Kilogram g kg A little heavier than a paper clip Almost nine sticks of butter 0.035 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 0.039 inches Liter militer L mL Just over a quart of milk A little less than ¼ teaspoon 1.057 quarts 0.03 fluid oz

Recording Metric Data Measure correctly Report findings precisely and accurately Scales on laboratory measuring devices vary Ex: Beaker – markings every 10 mL of volume Graduated cylinder marked to the milliliter Estimating

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

The Celsius Temperature Scale 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. Divided into 100 parts

Formulas for Converting Temperatures