August 18, 2014

SCIENTIFIC MEASUREMENT

Why is it important for scientists to use the same system/units of measurement?

GUIDING QUESTION #1

SYSTEMS OF MEASUREMENT

Why do we need a standardized system of measurement?

Scientific community is global.

An international “language” of measurement allows scientists to share, interpret, and compare experimental findings with other scientists, regardless of nationality or language barriers.

Problems with the “English” system of measurement

MAP OF COUNTRIES THAT USE ENGLISH SYSTEM OF

MEASUREMENT

The first standardized system of measurement: the “Metric” system

Developed in France in 1791 Named based on French word

for “measure” based on the decimal (powers

of 10)

International System of Units

Modernized version of the Metric System

Abbreviated by the letters SI. Established in 1960, at the 11th

General Conference on Weights and Measures.

Units, definitions, and symbols

METRIC SYSTEM & SI

COMPONENTS OF THE SI SYSTEM

The SI system of measurement has 3 parts:

1) base units

2) derived units

3) prefixesBase Unit: measure of the quantity that is defined to

be exactly 1

Prefix: modifier that allows us to express multiples or fractions of a base unit

What objects can you measure?

What properties can you measure?

GUIDING QUESTION #2

Distance (length, width, height)

TimeTemperatureMass Force (gravity)Amount of a substanceElectric currentLuminous intensity

MEASURABLE PROPERTIES

What objects can I can measure?

What property is being measured?

Come up with five examples of each measureable property coded in red on the previous slide.

EXAMPLES

What units are written with measurements of specific properties?

What tools are used for measurable properties?

GUIDING QUESTION #3

SI: BASE UNITS

Physical Quantity Unit Name Symbol

length meter m

mass gram g

time second s

electric current ampere A

temperature Kelvin K

amount of substance mole mol

luminous intensity candela cd

SI: DERIVED UNITS

Physical Quantity Unit Name Symbol

area square meter m2

volume cubic meter m3

speed meter persecond m/s

accelerationmeter per

second squared m/s2

weight, force newton N

pressure pascal Pa

energy, work joule J

SI AND ENGLISH UNIT COMPARISON

SI Units

Meter Gram Liter Kelvin Mol Cubic meter

English Units

Yard Ounce Quart Fahrenheit Troy ounce Bushel

Using your previous examples, answer the following questions for each one.

What units are written with measurements of specific properties?

What tools are used for measurable properties?

EXAMPLES

USING APPROPRIATE UNITS

In order to make our measurements as accurate and precise as possible, it is important to choose the most appropriate prefix to accompany the base unit.

For example, if I want to measure the distance & mass of a paper clip, I would use centimeters & grams. To find the distance & mass of an elephant, I would use meters & kilogram.

Prefix Symbol Numerical Multiplier ExponentialMultiplier

yotta Y 1,000,000,000,000,000,000,000,000 1024

zetta Z 1,000,000,000,000,000,000,000 1021

exa E 1,000,000,000,000,000,000 1018

peta P 1,000,000,000,000,000 1015

tera T 1,000,000,000,000 1012

giga G 1,000,000,000 109

mega M 1,000,000 106

kilo k 1,000 103

hecto h 100 102

deca da 10 101

no prefix means: 1 100

PREFIXES

PREFIXES

Prefix Symbol Numerical Multiplier ExponentialMultiplier

no prefix means: 1 100

deci d 0.1 10¯1

centi c 0.01 10¯2

milli m 0.001 10¯3

micro m 0.000001 10¯6

nano n 0.000000001 10¯9

pico p 0.000000000001 10¯12

femto f 0.000000000000001 10¯15

atto a 0.000000000000000001 10¯18

zepto z 0.000000000000000000001 10¯21

yocto y 0.000000000000000000000001 10¯24

SI PREFIXES

To help you remember the most practical SI prefixes, label this staircase and glue it in your notebook. You will need to memorize these!!

MEASUREMENT & PRECISION

The precision of a measurement depends on the instrument used to measure it.

For example, how long is this block?

MEASUREMENT & PRECISION

You should estimate one decimal point past where you can accurately measure, if the scale continues so that you can make an educated estimate.

Thus, the tool you use determines the number of significant figures used to report measurements.

Never estimate past the reading on a digital instrument.

HOW BIG IS THE BEETLE?

Copyright © 1997-2005 by Fred Senese

Measure between the head and the tail!

Between 1.5 and 1.6 in

Measured length: 1.54 in

The 1 and 5 are known with certainty

The last digit (4) is estimated between the two nearest fine division marks.

HOW BIG IS THE PENNY?

Copyright © 1997-2005 by Fred Senese

Measure the diameter.

Between 1.9 and 2.0 cmEstimate the last digit.

What diameter do you measure?

How does that compare to your classmates?

Is any measurement EXACT?

WHAT LENGTH IS INDICATED BY THE ARROW?