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SI Units

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SI Units. In science, we need to speak the same language 1795 French scientists develop metric system 1960 International committee meets to update the system and names it the “ Systeme Internationale d’Unites ” aka SI . SI Base Units. Seven SI base units Base unit

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SI Units

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  1. SI Units • In science, we need to speak the same language • 1795 • French scientists develop metric system • 1960 • International committee meets to update the system and names it the “SystemeInternationaled’Unites” aka SI

  2. SI Base Units • Seven SI base units • Base unit • A defined unit in a system of measurement that is based on an object or event in the physical world

  3. Tools of the Trade • Mass Scale that measures GRAMS not POUNDS • Pounds are used to measure the force of gravity on your mass…we want to measure the amount of STUFF (Matter) in a thing • Temperature thermometer measures the kinetic energy (KE) /movement of particles • Faster moving particle=more (KE)=higher temp (HOT) • Slower moving particles=less (KE)=cooler temp (COLD) • Volume amount of space object takes up… • ruler, measuring tape, etc to measure meters3 (l x w x h) • OR graduated cylinder to measure LITERS • Measure volume at the MENISCUS (curve or dip in the water)

  4. SI Derived Units • Not all quantities can be measured with base units • More than one base unit can be used • Speed limit is measure in…. • MPH • Miles per hour • Which is a combo of what base units? • Length and time

  5. Derived Units

  6. Common derived units we will use • Speed • Base unit of length and base unit of time • Meters/second • Volume • 3 base units of length • Length x length x length • 1 cm3 = 1 mL • Density • Mass/volume • Ratio that compares mass of an object to its volume • g/cm3 or g/mL

  7. Density • Density=mass divided by the volume • D=m/V • Gram/L or grams/m3 • How do we figure out volume of odd shaped objects…say a paper clip? • Water Displacement • What happens when you fill up the bath tub to the rim and then get in?

  8. Archimedes Principle • Measure known amount of water in graduated cylinder and record VOLUME (mL) • This is initial volume (Vi) • Drop in odd shaped object (paper clip) • Record the NEW volume of water • This is final vlume (Vf) • Subtract Vi from Vf to get volume of object (Vo) • Vo = Vf- Vi • Get the mass of the paper clip form the scale • Plug the mass (g) and volume (L) into density formula to figure out the density of the paper clip

  9. Prefixes Used with SI units

  10. Temperature • SI unit? • Kelvin • Our thermometers measure Celsius • To convert from Celsius to Kelvin • 0o C + 273 = 273 K • To convert from Kelvin to Celsius • 373 K - 273 = 100o C

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