Chapter 1The Nature of Science

Standards of MeasurementAccurate measurement is needed in a

valid experiment.Standard—an exact quantity that

people agree to use for comparison.In order for a measurement to make

sense, it must include a number AND a unit.Examples: 150 ft, 35 cm, 64 mi

Measurement SystemsUS: English system (pounds, feet, inches,

Fahrenheit)Most other nations: metric systemScience Worldwide: an improved

version of the metric system called “International System of Units” or SI units. SI comes from the French Le Systeme

Internationale d’Unites It is easier to convert units and share with

others around the world.

The SI SystemSI Measurements and Base units

Base unit for length is the meter (m)Converted unit: centimeter, kilometer

Base unit for mass is the kilogram (kg)Converted unit: gram, milligram

Base unit for time is the second (s)Converted unit: microsecond

Base unit for electric current is the ampere (amp)

Base unit for temperature is the kelvin (K) Base unit for volume is the liter (L)

The SI SystemThe SI system is based on the number 10.Prefixes are used with the names of the units to indicate

multiples of 10.

Prefix multiplying factor kilo = 1000 (thousand) deci = 1/10 or 0.1 (tenth) centi = 1/100 or 0.01 (hundredth) milli = 1/1000 or 0.001 (thousandth) micro = 1/1,000,000 or .000 001 (millionth) nano = 1/1,000,000,000 or 0.000 000 001(billionth)Something Called SI

Derived UnitsDerived Unit: a unit that

combines different SI unitsCommon Derived Units:

Area: cm2 or m2

Volume: cm3 or m3

Density: g/mL or g/cm3

Transition

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How can an aircraft carrier float?

What is density?

It is a derived unit.

Density= mass divided by volume.

How do you determine mass? Use a balance.

Measure in grams or kilograms.

Mr. Edmonds Rock to an Oldie

How do you determine volume?

We will express volume in cm3 and mL.

For a rectangular prism, V= L x W x H

For a liquid, measure volume using a graduated cylinder

.Find density first 90 seconds approximately no sig figs

Base units Meters Liters and Grams focus on liters

Density=mass volume

Because 1 cm3 = 1 mL

Density=m (grams) = m (g)

V (cm3) v (mL)Example:

D=62.4 g/ (8.5 cm x 2.5 cm x 3.3cm)=

D=62.4 g/ 70.1 cm3 = .9 g/ cm3

Accurate Measurement ReadingsRead to the nearest mark, then estimate

the number one decimal place further.

49.6 can be read with the lines on the rulerEstimate the last digit

49.66 cm

47.1 can be read with the lines on the ruler Estimate the last digit

47.10 cm

6.1 can be read with the linesEstimate the last digit

4.4 can be readEstimate the last digit

Dimensional AnalysisSometimes things need to be

converted to different units.You can use a conversion factor

(a ratio) to change one unit to another.Ex. 1 in = 2.54 cm

This process is called dimensional analysis

Conversion Process5 Steps of Dimensional Analysis

1. Start with the given (number & unit)

2. X (times)

3. Write the conversion factor as a fraction with the given unit on the bottom and new unit on top

4. Cross out units that cancel5. Calculate & write the correct answer &

units

Example: How many centimeters is 6.74 in?1. Start with the given (number & unit)

2. X (times)

3. Write the conversion factor as a fraction with the given unit on the bottom and new unit on top 1 in = 2.54 cm

4. Cross out units that cancel5. Calculate & write the correct answer &

units 6.74 in 2.54 cm1 in

= 17.12 cmX

Metric Conversions: The Ladder Method.

KILO1000

kHECTO

100h

DEKA10da

DECI0.1d

CENTI0.01

cMILLI0.001

m

MetersLitersGrams

seconds

Ladder Method

How do you use the “ladder” method?

1 – Determine your starting point.

2 – Count the “jumps” to your ending point.

3 – Move the decimal the same number of jumps in the same direction.

4 km = ________m

12

3

How many jumps does it take?

Starting Point

Ending Point

4. 1

_

_.2_

_.3_

_.= 4000 m