Introduction to Physical Science/1.5

The SI System

"SI" or "System International" is the worldwide (excepting the US and Liberia) system of measurement. This system includes units of each dimension, but its defining feature is its basis on the number 10. Old english units (also known as the customary system) where based on units of 12 which, although the system stood for centuries, where not as effective as the current SI measurements. The SI system is sometimes also known as the "Metric" system. Below are the common units within the SI system.

Units

Length, Width, Height

mm - millimetre: equal to .001 metres

cm - centimetre: equal to .01 metres

m - metre: one metre

hm - hectometre: equal to 100 metres

km - kilometre: equal to 1000 metres

Area

cm^2 - square centimetres: equal to a square with length and width of 1cm

km^2 - square kilometres: equal to a square with length and width of 1km

Volume

cm^3 - cubic cetimetres: equal to a cube with length, width, and height of 1cm

mL - millilitre: .001 liters

cL - centilitre: .01 liters

dL - decilitre

L - litre: one liter: equal to one cubic decimetre

daL - decaliter: 10 liters

hL - hecto litres: 100 liters

Mass

mg - miligram .001 gram

cg - centigram .01 gram

g- gram: one gram

dag - decagram: 10 grams

hg - hecto gram: 100 grams

kg - kilo gram: 1000 grams

The Common Conversions

The common system has much different values and uses different terminology for different measurements. Below are the differences between the two systems discussed in depth. Only measurements representing the same physical quantities con be "converted".

Mass vs. Weight

Where the SI system uses Mass, the Common System uses Weight. The two words mean different things. Weight is the effect of the force of gravity on an object's mass. Although weight depends on mass, it is not the same thing as mass. Mass is the amount of matter (material) that exists within an object (we will discuss matter in depth in chapter 1.6). Mass cannot be "converted" to weight, but rather a calculation involving Newton's Second Law of Motion must be used. It is, however, common practice to use the conversions listed below based on the standard acceleration due to gravity here on the earth. This should be further explored when studying motion and forces.

Volume

Volume is very different between the common and SI systems. In the common system the standard units for volume were the flow ounce and the pint. The two have no basis in the SI system and are only converted by sheer mathematical terms. The conversion factors can be found below.

Conversions

Mass

1 kilogram = 2.2 pound

1 pound = 0.45 kilograms

Volume

1 Liter = 33.81 fluid ounces 1 fluid ounce = .029 liters

1 Liter = 2.11 pints

Vocabulary and Questions

• Length is the distance from a given point A to a given point B
• Weight is the measure of the effect that gravity has on an object
• Mass is the amount of matter in a given object
• Volume is the amount of space an object takes up
• Conversion is the method by which units in one system are measured against those in another

Covering The Reading

1. Based on your observations, what do the following prefixes mean? kilo, deca, deci, milli, centi, hecto
2. What does SI stand for?
3. What country did the metric system originate in?
4. How many pints are in a liter?
5. What number are SI system units based on?

Critical Thinking

1. Using the

Exploration

1. Collect containers from around your house check the units on their labels, construct a table that shows the conversions between the customary and metric units.