Units of Measurement Chapter 1.2 Notes

Measuring Physical Quantities Examples include length, time, mass, weight, volume, energy, temperature, heat, and density Two major system units: United States Customary System (USCS) Used in U.S. for nonscientific purposes (height, length of the football field, etc.) Système International (SI) or the metric system Used in most other nations Used by scientists all over the world, including those in the U.S.

The “SI” System Physical QuantityMetric UnitAbbreviation lengthmeterm masskilogramkg volumeliterL temperaturekelvin/CelsiusK/C timeseconds amount of substance molemol

The Metric System Uses a decimal system Easier to convert between units All units are related to smaller or larger units by a factor of 10

Metric Prefixes NameSymbolMeaning Giga-G1,000,000,000 Mega-M1,000,000 Kilo-k1,000 Hecto-h100 Deka-da10 (base) Deci-d0.1 Centi-c0.01 Milli-m0.001

Mass vs. Weight Mass is the quantitative measure of how much matter a material object contains. Measured in kg, g, mg A gold bar that is twice as massive as another gold bar has twice as many gold atoms Weight is the gravitational force exerted on an object by the nearest most massive body, such as the Earth. Depends entirely on the objects location You weigh less on the moon than you do on the Earth because the moon is less massive than the Earth. Measured in pounds and tons

How to Measure Mass If it is a “nonmessy” solid, simply weigh it on a scale If it is a liquid or “messy” (a powder, greasy, etc.), use a weighing tray or a beaker. Weigh the empty weighing tray or beaker and record its mass. Add the object to the weighing tray or beaker and weigh it. Subtract the mass of the empty tray or beaker to get the desired mass.

Scale Rules Gently place objects on scales. Make sure the scale is clean prior to using it AND when you are finished (wipe off excess powder, etc.) Make sure that before you use it, the scale reads 0.00 g. If it doesn’t, press ON/ZERO before weighing your solid.

Volume The amount of space a material object occupies. SI unit is the liter (L) Measuring volume: If it is a cubic solid, measure the length, width, and height, and multiply them. (l x w x h = v) If it is a liquid, pour it in a graduated cylinder and read from the meniscus (low point of the curve) meniscus

Measuring the volume of an irregular solid Pour water into a graduated cylinder that is large enough to hold the solid. Read the volume of the water. Place the solid into the water, but be careful to not spill any water. Read the new volume. Subtract the new volume from the old in order to get the volume of the solid.

Measuring Accurately Always report ALL numbers given on a digital readout (do NOT round) Do NOT add or delete zeros to the end Make sure your reading is stable Always read your equipment as accurately as you can, take your time, get close to the instrument

Measuring Techniques Estimate one place on non digital equipment. (rulers, graduated cylinders) 6 7 cm 6.42 cm If it is exactly on the line 6.60 cm

Measuring Precisely If possible, always measure three times If one measurement isn’t close to the others, always measure again It’s a good idea to have your lab partner take the same reading as you to make sure you are reading it correctly

Classwork/Homework Worksheet: “Skills Test B: Measuring and Calculating”