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 gramsYour 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 = 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

Prefix 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

Metric Prefixes (chart on page 63)

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

Comparing Systems(Comparison Chart)

Recording Metric Data

Estimating Measure correctly Report findings

precisely and accurately

(Estimating con’t) Scales on laboratory measuring devices varyEx: 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 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 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 1742.

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.