Transcript Chapter 1 Legacy

Chapter 1 Legacy
On Units of Measure
The Metric System
• In the past, many different units were used to
measure things (ex. Foot, cubit, furlong,
fathom)
• However, these units cannot be universally
understood and repeatable, so scientists
established the International System of Units
(SI), better known as the metric system.
• First, it is important to understand the
meanings of QUANTITIES and UNITS. It can
sometimes be difficult to tell the difference.
Quantities and Units
Quantities
• The amount of a specific
dimension
• Includes Length, Mass,
Time, Temperature, etc.
Units
• The standard sizes that you
measure quantities in
• Includes meter, kilogram,
second, foot, pound, mile,
etc.
Fundamental vs. Derived Units
• Fundamental units are base units that form
the building blocks of all other measured
units. They are universally understood and
repeatable.
• Derived units are units made up of
fundamental units, ex. m/s, kg/m^3,
g*cm/s^2
There are 7 fundamental
units/quantities in all…
• You should already be familiar with 3…
– Meter (Length)
– Kilogram (Mass)
– Second (Time)
• And then there are these…
– Ampere (Electrical Current)
– Kelvin (Temperature)
– Mole (Amount of Substance)
– Candela (Luminous Intensity)
If you needed to, you could try using a
pneumonic device to remember.
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My
Killer
Snake
Ate
Kittens
Moles and
Cows
Defining Fundamental Units
• A meter, for example, is today defined as the
distance light travels in 1/2999792458 of a
second
• This may seem ridiculously complex, but it is
necessary to define it this way to make it
universally understood and repeatable
• The speed of light is one thing commonly
incorporated into these definitions because it can
be universally understood and repeatable
anywhere in the universe.
Systems of Measurement
• There are 3 popularly used systems of measurement,
the third being British. They’re named by the primary
fundamental units of the system and abbrieviated.
• mks- meter, kilogram, second
• cgs- centimeter, gram, second
• fps- foot, pound, second
• *It is important to realize that technically, a pound is
not a unit of mass, but of force. Your weight in pounds
is subject to change under different gravity (like on the
moon), but your mass in kilograms isn’t, no matter
where you are.