Measurements August 24, 2015 (2.1 in your books)

Meme Moment After exploring the science stockroom and finding all that decaying food...

Scientist of the Day Practice observation and inference. What can you see? What can you (scientifically) guess based on what you see? Is your observation qualitative or quantitative? Objective or subjective? What biases do you have?

Margaret Hamilton Started off as a teacher (math & French) Went back to grad school to learn about programming before it was even a thing Computer programmer for Apollo 11 mission Software design still used today Made sure moon landing happened Entrepreneur Also headed MIT instrumentation lab. Here she’s standing with all of the code for the Apollo 11 mission. TI-89 calculators are better computers than the giant room-sized computers she had to work with back then!

Metric System Replaced weird measurements like “hands” or “cubits” that vary from place to place, as well as miles A cubit is the length of your fingertip to your elbow Based around water, which is the same everywhere 1 g of water = 1 cm3 = 1 mL (at 4ºC) Once you have a unit, you can add a prefix to save space. The sun is 150,000,000,000 m away has a lot of 0s to keep track of The sun is 150 billion m away has words in it, so you can’t do math The sun is 150 Gm away(gigameters) Compare your arm to the person next to you. Are they the same length? See how people might get confused about cubits?

Imperial vs Metric Measurement Imperial Metric length inches, feet, yards, miles, leagues meter volume ounces, pints, quarts, gallons liter mass grains, pounds, stones, slugs gram

Who doesn’t use the metric system? Scientists EVERYWHERE use the metric system though.

Different ways of writing the same thing Prefixes 6th and 7th grade Symbol Prefix Math 10n Example k kilo x 1000 x 103 kilogram h hecto x 100 x 102 hectometer da deka x 10 x 101 dekaliter x 1 liter d deci x 0.1 x 10-1 decimeter c centi x 0.01 x 10-2 centimeter m milli x 0.001 x 10-3 milligram There are other types of prefixes too, and they sneak into all sorts of words. E.g. “terabytes,” “gigahertz,” etc. Memorize this chart! Different ways of writing the same thing

Different ways of writing the same thing Prefixes 8th grade Symbol Prefix Math 10n Example k kilo x 1000 x 103 kilogram h hecto x 100 x 102 hectometer da deka x 10 x 101 dekameter x 1 liter d deci x 0.1 x 10-1 decimeter c centi x 0.01 x 10-2 centimeter m milli x 0.001 x 10-3 milligram µ micro x 0.000001 x 10-6 microliter n nano x 0.000000001 x 10-9 nanogram There are other types of prefixes too, and they sneak into all sorts of words. E.g. “terabytes,” “gigahertz,” etc. Memorize this chart! Different ways of writing the same thing

SI Units Fancier version of the metric system “International system of units” The acronym doesn’t match because it’s international. Acronym comes from the French version Système International d'Unités 7 base quantities – if you know these, you can describe any quantitative measurement. Everything we know for certain is based on those 7 types of numbers We’ll use other units/descriptions/symbols like “energy” or “density” or “power,” but we can always trace them back to SI units Energy = Joules = J = N·m = kg·m2/s2 This is background info. You don’t have to know this for tests.

SI Units K = Kelvin = temperature s = second = time m = meter = length kg = mass = how heavy (ish) cd = candela = how bright mol = mole = amount of stuff A = ampere = electric current For now, we care about the first 4 symbols. Note that “liter” and “degrees Celsius” aren’t base SI units even though scientists use them all the time.

Length Length: distance from one point to another SI unit = meter = m Estimating: 1 m ≈ 1 yard = 3 feet 1 cm ≈ the width of your finger 1 km ≈ 0.6 miles

Time Time: the period between 2 events SI unit = second = s Sometimes scientists get lazy and say “hours” or “days” instead of “____ kiloseconds” Milliseconds, etc are really popular in sports though!

Mass Mass: the amount of matter in an object Not the same as weight! SI unit = kilogram = kg Weight: the pull of gravity on an object. Mass and weight only match on earth. In space, objects have 0 weight. A 5 kg object on earth still has 5 kg mass in space – just have to measure it differently!

Temperature Temperature: energy of molecules moving Molecules are always moving! Lots of moving = high temperature, hot Almost still = low temperature, cold SI unit = Kelvin = K Metric system also uses Celsius = ºC K = 273 + ºC Temperature is weird. It’s not the same thing as “heat,” even though we talk about hot and cold. We’ll talk about this more when we do states of matter.

Temperature Scales Molecules stop moving at absolute zero.

Breaking Down SI Units Common measurements like “volume” and “density” don’t have their own SI unit, but we can still trace their metric system name to an SI unit Volume = liter = L How much 3D space something takes up Everything is based on water, so 1 mL = 1 cm3 Going back to SI units, 1 L = 0.001 m3 = 1 dm3 Density is commonly g/mL or g/cm3 Depends if you’re talking about liquid or solid 1 g/mL = 1 g/cm3, so they’re really the same thing Example of “mixing and matching” SI units to make a new measurement

Volume Volume: Measures 3D space. Metric unit is liters (L). SI unit is cubic meters (m3). Often use milliliters also (mL) Estimating: 1 coke can ≈ 350 mL 1 cup (for baking) ≈ 250 mL 1 gallon of milk ≈ 4 L Squiggly equals sign means “about”

Measuring Volume Taller/longer is better than stumpy Easier to see the measurements Measure at eye level Real number is at the bottom of the meniscus (the dip) Water has a big meniscus because of adhesion – it likes to stick to other things! Glass and mercury have an upside-down meniscus

Density Density: how much mass is in a given volume. SI unit = kg/m3 Combines mass and volume. Common metric measurements are g/mL and g/cm3 Things float if they are less dense than the liquid Things sink if they are more dense When things are the same substance, they always have the same density. Water is always 1 g/mL (at 4ºC) If you forget the formula for density, look at the units to remind yourself.

Density Formula

Density Formula “mnemonic” *just like we love comic sans. Not.

Eureka! Archimedes was asked to figure out if a crown was made of real gold and if it was all the gold the king had given to the jeweler. It weighed the right amount, but what if another metal had been added to make up the difference? He couldn’t do the normal tests because that would break the crown He yelled “Eureka!” when he figured out he could use density to test it He stepped into a bath and it overflowed – displaced volume We still use his method

Questions Any questions about the slides? Any new questions?

Old Questions What is the most dangerous big cat? What is the most dangerous fish apart from sharks? What kinds of water snakes are venomous? Where is West Nile virus and what does it do? Picture of largest snake? How many scientific laws are there? What is fugacity? How do spitting cobras work?