Introduction to the International System of Units (SI) and the Metric System Mr. Tang and Mr. Pulickeel SPH3U1 September 2008
In the beginning Back in the day (1000s of years ago) when people built things themselves, it wasn’t necessary to measure things because everyone did it themselves. I need a bolt as wide as thumb
What you talkin’ ‘bout Willis? However, projects became more complicated, it became necessary to have others work different parts, therefore they had to standardize measurement. Sir, I don’t know what your thumb looks like… moron …
Birth of Imperialism So they decide to take the most popular guy, measure his thumb and call it an inch. This guy was the King! An inch was the width of a thumb A foot was the size of the kings foot, which eventually became 12 inches. A yard was the distance from the tip of a man's nose to the end of his outstretched arm. Eventually, 3 feet became a yard
Other systems The British empire used this method to devise measurements for mass, volume and time. For instance a pound was equal to 7002 troy grains Other countries developed their own units of measure 7001? That’s stupid! A pound should be 7002 … Your sands are no match for our stones! What’s a troy grain? We use wheat seeds
Sacre Bleu! C’est tres confusant! In 1586, the Flemish mathematician Simon Stevin published a small pamphlet called De Thiende ("the tenth"). He thought counting by decimal fractions would be really nifty! His idea was slow to catch on… I also invented the land yacht! It’s a wagon with sails… WEEEEE!
Vive Le France! Eventually (in the 1800s), the French adopted the Metric System. In the 1970s many commonwealth (former British colonies) switched to the metric system.
SI Units of Measurement When working with numbers, it is necessary to distinguish between the quantity and its units Quantity describes something that has magnitude, size or amount (mass, length, etc...) Units is a quantity adopted as a standard of measurement (kg, m, etc...)
The Super SI Seven! UnitSymbolQuantity kilogramkgmass metremlength secondstime ampereAelectric current kelvinK thermodynamic temperature molemolamount of substance candelacdluminous intensity
GRAMS! It is currently defined by one thousandth of the mass of a specific Pt/Ir mass that is kept in a vault in France There are efforts underway to redefine it in terms of physical quantities that could be reproduced in any laboratory with suitable equipment. The gram was originally one millionth of the mass of a cubic metre of water The SI unit is kg
METRE! Then it was defined as 1 ⁄ 40 000 000 the earth’s circumference It is now is defined as the distance travelled by light in an absolute vacuum during 1 ⁄ 299,792,458 of a second The metre was defined as the length of a particular bar of platinum-iridium alloy It was then defined as the wavelength of light emitted by a specified atomic transition;
SECONDS! It was redefined in 1967 to be 9,192,631,770 periods of vibration of the radiation emitted at a specific wavelength by an atom of caesium-133 The second was originally 1 ⁄ 86,400 of the mean solar day There are plans to redefine it as something which can be reproduced in any equipped lab
Temperature! SI unit is the Kelvin (K), a scale whose units have the same "size", but which starts at absolute zero. Zero degrees Celsius equals 273.15 K NOTE: ° is no longer to be used with Kelvins The Celsius temperature was defined as a scale with 0°C being defined as its freezing point and 100°C being defined as its boiling point at a pressure of one standard atmosphere.
Moles! The currently accepted number of atoms in 12 grams of Carbon-12 is 6.02214179×10 23 atoms. This number is called Avogadro's Constant A mole is the amount of a substance which contains as many elementary entities as there are atoms in 12 grams of Carbon-12
Moles! For example, Iron (Fe) has a atomic mass of 55.84 u, so a mole of iron has a mass of 55.845 grams. This notation is very commonly used by chemists and physicists. The relationship of the atomic mass unit (u) Avogadro's number means that a mole can also be defined as: the quantity of a substance whose mass in grams is the same as its formula weight.
Amperes and Candelas! A Candela is a measure of the power emitted by a light source in a particular direction. A common candle emits light with a luminous intensity of roughly one candela. An Ampere is a measure of Electrical Currents. We will learn about this later on.
Imperial Systems Today, the entire world is metric, except for the US, Myanmar and Liberia
Zut Alors! The French tried to implement Metric Time in September 1794. They divided the day into 10 decimal hours. One decimal hour equaled 100 decimal minutes and each decimal minute equaled 100 decimal seconds It was suspended 6 months later…
Counting Metric The great thing about the metric system is that everything is counted by bases of 10! PrefixPowerSymbol exa10 18 E peta10 15 P tera10 12 T giga10 9 G mega10 6 M kilo10 3 k base unit10 0 milli10 -3 m micro10 -6 μ nano10 -9 n pico10 -12 p femto10 -15 f atto10 -18 a