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.
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
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
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
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 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.
1 kilogram = 2.2 pound
1 pound = 0.45 kilograms
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
- Based on your observations, what do the following prefixes mean? kilo, deca, deci, milli, centi, hecto
- What does SI stand for?
- What country did the metric system originate in?
- How many pints are in a liter?
- What number are SI sytem units based on?
- Using the
- 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.