CH 2: Phys. Sci. Methods The goal here is for you to learn how to take measurements using the SI system and to create quality graphs from data you collect.

Units and Standards Standard- An exact quantity that people use for comparison. Example: a meter; you could measure 0.5 meters, 80 meters, etc.

Measurement Systems A measurement must have a number and a unit in order to make sense. How tall are you? Number: Unit:

Measurement Systems ALWAYS include a unit. Together lets list some other examples:

The SI system SI = the International System of Units; the standard system of measurement used worldwide. Each type of measurement has a base unit.

The SI system What is the SI base unit for length? The SI system is easy to use because it is based on powers of 10.

The SI system A prefix is included with the base unit to indicate what power of ten should be used with the base. Example: 1 kilo gram is equal to ________ grams

SI Prefixes PrefixSymbol Multiplying Factor kilo-k1,000 hecto-h100 deka-da10

SI Prefixes PrefixSymbol Multiplying Factor deci-d0.1 centi-c0.01 milli-m0.001

Base Units & Symbols Quantity Base Unit Symbol LengthMeterm Massgramg TimeSeconds

Base Units & Symbols Quantity Base Unit Symbol TemperatureKelvinK CurrentAmpereA AmountMolemol

QuantityTool Length Meter stick MassBalance Temp.Thermometer Volume Ruler (solid) Volume Graduated cylinder TimeSecond

Choosing a Unit The unit you use to measure with will depend on the item being measured. Example: what unit would best describe the length of a finger?

Choosing a Unit Lets list some things we could measure and the best units to use:

Converting Measurement You measure the width of your computer desk as 0.75 m. You’re buying a computer and want to make sure it will fit, but it is listed as 40 cm wide. Will it fit?

Converting Measurement kilo-hecto-deka-meter-deci-centi-milli Conversions are made easy using the code above. When converting, simply move the decimal to the left or right as many times as necessary.

Converting Measurement kilo-hecto-deka-meter-deci-centi-milli To convert cm to m, move the decimal 2 spaces left = 0.4 m 40.0 cm = 4.0 dm

Volume It is the amount of space occupied by an object. The volume of a solid is calculated by multiplying the objects: length X width X height the units for the volume of a solid = cm 3

Volume The volume of a liquid is measured using a graduated cylinder. The units for the volume of a liquid = mL (see next slide)

The water level

Accuracy How close your measurement is to the actual amount, length, etc. WE NEED TO MAKE ACCURATE MEASUREMENTS

Significant Digits Basically means how detailed your measurement is. The length of our textbook is ________ cm Why can’t we make a more accurate measurement with a ruler ???

H2OH2OH2OH2O We can only estimate one decimal point when making measurements.

H2OH2OH2OH2O Here, we know the water level is between 8.0 mL and 8.5 mL, so my reading is 8.3 mL.

123 cm Here we know the measurement is between 2.2 cm and 2.3 cm. What is your most accurate measurement here? Significant Digits

MASS! Mass - The amount of stuff in an object. Mass does not change unless part of the object is removed or something is added to it. Measured in kilograms (kg)

Density Density - Mass per unit volume of an object. It’s measured in g/mL or g/cm D= M V mass volume 3

Ticking away Time - between 2 events. The interval

Temperature Temperature – A measure of how hot or cold something is. Usually measured in degrees Celsius where water freezes at 0º C and boils at 100º C

Temperature May also be measured in degrees Fahrenheit where water freezes at 32º F and boils at 212º F

Temperature May also be measured in SI units of kelvin (K). To convert from ºC to kelvin use the formula: kelvin = ºC ºC = kelvin - 273

Temperature Additional formulas you must be able to use: kelvin = ºC ºC = 5/9 × (ºF – 32) ºF = 9/5 × ºC + 32

Graphing is Fun ! Graph - visual display of info or data. Types of graphs include: 1.Line graphs - Used to show trends (how data changes over time) y-axis (vertical line) shows the dependant variable or what you are measuring x-axis (horizontal line) shows the independent variable or what you control

Graphing is Fun ! Interpolation - a way of finding information between values that are known Extrapolation - a means of obtaining values for quantities beyond those that are known.

Example of a Line Graph XY

Graph Types continued 2.Bar graphs- Used to compare information collected by counting.

Graph Types continued 3.Circle graphs- Used to show the percentage breakdown of a whole.