si units in science, we need to speak the same language in science, we need to speak the same...
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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
A defined unit in a system of measurement that is based on an object or event in the physical world
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)
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
Derived Units
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
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?
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
Prefixes Used with SI units
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