SI Units In science, we need to speak the same language In science, we need to speak the same language 1795 1795 French scientists develop metric system.

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