Nature of Science. The International System of Units

we wanted to measure a 2 x 4 for building a house.

Numbers by themselves don’t make sense.

A board is 350 long . . . .

A board is meters long . . . .

Units by themselves don’t make sense.

To make sense, all measurements need both . . .

A Number

and

a Unit!

amount to determine the size of the new object.

Helps to make a rough measurement of an object.
Usefully when you are in a hurry and exact numbers are not required.

other.

Precision and Accuracy

Accuracy is comparing your measurement to the actual or accepted value.

than the English system

Scientists use the SI System worldwide because:

Why use the SI System?

In the U.S. we use the English or Standard System, most of the rest of the world uses the Metric or SI System.

The SI (International System of Units) system is the form of measurement typically used by scientists.

of matter in an object

Volume: measures the amount of space something takes up

Other Types of measurement include:

time
temperature
density
PH

that everyone agrees to use as a basis of comparison.

. . .

12 inches in a foot
3 feet in a yard
5,280 feet in a mile
16 ounces in a pound
4 quarts to a gallon

In the SI System you only have to remember one number.

The SI System is based on the number 10.

any
SI measurement.
The UNIT becomes whichever type of measurement you are making. (mass, volume, or length)

It is the same system regardless if you are measuring length, mass, or volume.

.

Volume then it is the liter (deciliter, hectoliter, etc.)

The first part of the term indicates the amount, the second part indicates the type of measurement.

centi

gram

Mass then it is the gram (centigram, milligram, etc.)

Length then it is the meter (kilometer, decameter, etc.)

SI System is very easy.
For Example in the English system if you wanted to know how many inches in 2 miles what would you do?

Take the number of miles (2).
Multiply it by the number of feet in a mile (5,280).
Multiply that by the number of inches in a foot (12).

ANSWER: 126,720 inches in 2 miles

if you wanted to know how many centimeters were in 3 meters, what would you do?

Kilo Hecto Deca UNIT Deci Centi Milli

3 meters =

300 centimeters

Find the unit you have (meters).
Find the unit you are changing to (centimeters).
Count the number of units in-between (2).
Move the decimal point that many spaces, in the same direction you counted (right).

Milli

2,321.0 millimeters to meters

521.0 grams to hectograms

8.5 kiloliters to centiliters

= 2.321 meters

= 5.21 hectograms

= 8,500,000 centiliters

NOTE: The digits aren’t changing, the position of the decimal is. In the English system the whole number changes.

Basic units of Measurement (meter, liter, gram)
How to convert metric units
Vocabulary words

of matter in an object

Volume: measures the amount of space something takes up

In SI the basic units are:

Length is the meter
Mass is the gram
Volume is the liter (liquid)
Temperature is Celsius

is width, height, depth, etc. All are length measurements.
The basic unit of length in the SI System is the meter.
The meter is about the length of the English yard (3 feet).
Area is a variation of a length measurement.
Area is length x width.
Expressed in units2 (m2, cm2, mm2 etc.)

Metric Measurement: Length

in an object.
Basic unit of mass is the gram. There are 454 grams in one pound.
Weight and mass are related, but NOT the same.
Weight is the pull of gravity on an object
The greater the mass, the larger the pull of gravity.

something takes up.
The basic unit used for volume is the liter. This unit is used for the volumes of liquids.
Volumes of solids are figured using this formula:

(L)ength x (W)idth x (H)eight

cm x cm x cm = cm3

Objects without a definite length, width or height (a rock for example), can use water displacement to determine volume. NOTE: 1 ml = 1 cm3

the atoms in an object.
Temperature is measured with a thermometer and measured in Celsius or Kelvin.
Celsius ranges from 0 (freezing) to 100 (boiling).
The Kelvin scale begins at absolute zero, or 0 K. At 0 Kelvin no more heat can be removed from an object.
To convert to Kelvin you add 273 degrees to the Celsius reading.
Freezing in Kelvin is 273 K, boiling is 373 K.

a kilogram of lead?

Which one takes up more space (volume)?

They are both one kilogram so they weight the same, but it takes more feathers than lead to equal one kilogram!

We say the lead is more dense than the feathers.

Density is how much matter is in something (mass), compared to the amount of space it takes up (volume).

The formula for density is:

Every substance has a density, and that density always remains the same.
Density can be used to figure out what an unknown substance is.
The density of water is 1 g / cm3

So the unit for density is g / cm3

Mass (grams)

divided by

Volume (cm3)