# SI Units Système International d‘Unités

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SI Units Système International d‘Unités OK, I really meant measuring things using the metric system. Used all over the world except the US 

SI Basics Le Systeme international d'Unites officially came into being in October 1960 and has been officially recognized and adopted by nearly all countries. It is based upon 7 principal units: Type – Unit – Abbreviation Length - metre - m Mass - kilogram - kg Time - second - s Electric current - ampere - A Temperature - kelvin - K Amount of substance - mole - mol Luminous intensity - candela - cd

But Where did it all come from?
They felt that it had to be based in real things scientists and others could relate to – things like Water, the Earth, candles, and things getting hotter. Believe it or not – SI tries to keep it simple. And all based in Powers of Ten. (video) ( )

It’s all about Water – H2O & the Size of the Earth
It all started with figuring out the distance between the equator and the North Pole, then dividing that by 10,000,000! That became a meter. OK – it was supposed to be a meter, later they obtained better measurements of the Earth’s size, and instead of changing the Meter, just made the it a standard size. A meter is also a convenient size for human measurement.

Length to Volume & Mass Once you had a Metre, you could subdivide that into 10 units – decimeters. You could cube that to make a cubic decimeter, also called a Liter. Fill a Liter with water and it’s mass is 1 Kilogram.

Meter or Metre OK – the official unit is the Metre – and that goes back to the French. We usually call it a Meter – the English version

The Basics - again metre [m] kilogram [kg] second [s] ampere [A]
The metre is the basic unit of length. It is the distance light travels, in a vacuum, in 1/ th of a second. kilogram [kg] The kilogram is the basic unit of mass. It is the mass of an international prototype in the form of a platinum-iridium cylinder kept at Sevres in France. It is now the only basic unit still defined in terms of a material object, and also the only one with a prefix[kilo] already in place. second [s] The second is the basic unit of time. It is the length of time taken for periods of vibration of the caesium-133 atom to occur. ampere [A] The ampere is the basic unit of electric current. It is that current which produces a specified force between two parallel wires which are 1 metre apart in a vacuum.It is named after the French physicist Andre Ampere ( ). kelvin [K] The kelvin is the basic unit of temperature. It is 1/273.16th of the thermodynamic temperature of the triple point of water. It is named after the Scottish mathematician and physicist William Thomson 1st Lord Kelvin ( ). mole [mol] The mole is the basic unit of substance. It is the amount of substance that contains as many elementary units as there are atoms in kg of carbon-12. candela [cd] The candela is the basic unit of luminous intensity. It is the intensity of a source of light of a specified frequency, which gives a specified amount of power in a given direction.

Prefixes yotta [Y] = 10^24 zetta [Z] = 10^21 exa [E] = 10^18 peta [P] = 10^15 tera [T] = 10^12 giga [G] = 10^9 (a billion) mega [M] = 10^6 (a million) kilo [k] = 10^3 (a thousand) hecto [h] 100 = 10^2 (a hundred) deca [da]10 = 10^1 (ten) 1 = 10^0 deci [d] 0.1 = 10^-1 (a tenth) centi [c] 0.01 = 10^-2 (a hundredth) milli [m] = 10^-3 (a thousandth) micro [µ] = 10^-6 (a millionth) nano [n] = 10^-9 (a billionth) pico [p] = 10^-12 femto [f] = 10^-15 atto [a] = 10^-18 zepto [z] = 10^-21 yocto [y] = 10^-24

Useful Prefixes giga [G] 1 000 000 000 = 10^9 (a billion)
mega [M] = 10^6 (a million) kilo [k] = 10^3 (a thousand) hecto [h] 100 = 10^2 (a hundred) deca [da] 10 = 10^1 (ten) 1 = 10^0 deci [d] 0.1 = 10^-1 (a tenth) centi [c] = 10^-2 (a hundredth) milli [m] = 10^-3 (a thousandth) micro [µ] = 10^-6 (a millionth) nano [n] = 10^-9 (a billionth)

Lets get Real - Length What units do we really use for length? And how big are they? Kilometers Meters Centimeters Millimeters Micrometers – Microns Ångström - angstrom

Getting Real - Mass Mass is Not Weight!!!!
What units do we really use for mass? How much is that really? kilogram gram milligram microgram

Mass is Not Weight? WHAT? Weight is the force of attraction between two objects. Your weight is the force of attraction between you and the Earth Mass is the amount of material (electrons, protons and neutrons) in a substance. The amount of “stuff”. It provides a gravitational attraction and has inertia.

Mass and Weight again Your mass doesn’t change! (unless)
Your weight changes, depending on where you are: On the moon – 1/6 On Mars – 1/3 On Jupiter – 2.5x In orbit - 0

Weighing the Earth 1 First – weigh yourself on a bathroom scale

Weighing the Earth 2 Now take the scale out to the curb of the road

Weighing the Earth 3

Getting real with Volume
Volume, the amount of Space things take up – is a “cubic” measurement – l x w x h We use two systems for Volume which are really the same  1 liter = 1000 ml = 1000 cm3 1 milliliter = 1 cm3 Occasionally we might use cubic meters m3 or cubic kilometers km3.

Volume How much is that really? Liter Milliliter

Measurement Activity Measure the following objects in m, cm, mm:
Your desk (l & w & h) The door Your height, your nose to finger tip, your foot, your “shaka”, the room. To convert m<->cm<->mm 1000 mm = 100 cm = 1 m 10 mm = 1 cm cm to mm: x10 mm to cm: ÷10 m to cm: x cm to m: ÷ 100 m to mm: x1000 mm to m: ÷ 1000

Object Meter Centimeter Millimeter Desk – L Desk – W Desk – H Door – H Door – W Room – L Room – W Your Height Nose to finger Foot Shaka

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Disclaimer Aloha I put together these power points for use in my science classes. You may use them in your classes. Some images are public domain, some are used under the fair-use provisions of the copyright law, some are mine. Copyright is retained by the owners! Ted Brattstrom

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