SI (Système International d’unités)

Metric System

Introduction

• The thermometer says 39°C.– Do you need a warm jacket or your shorts

• Your school is 2 km away.– Do you need a ride or can you walk?

• A box has a mass of 500 grams.– Can you lift this by yourself or do you need help?

• Milk comes in a 2 liter container.– Can you share with your friends, or do you only

have enough for yourself?

Measurement History

• Since the beginning of time people have been measuring– Earliest recorded measurements involved length• Egypt, 3000 BC

– Cubit– Palm– Digit

Length History

• Length units based on human body– Hand = width of human hand– Span = tip of pinky to tip of thumb– Foot = human foot– Cubit = tip of middle finger to elbow– Yard = tip of nose to thumb– Fathom = finger tip – finger tip of outstretched

arms– Mile = “mille passe” = 1000 double paces

Volume History

• Volume originally measured by heaps or handfuls– Gallon = container that held 10 pounds of water– Quarts = ¼ of gallon

Mass History

• Mass originally measured by stones or seeds– Grain = based on number of seeds– Carat = based on “carob” seed– Stones = based on stones– Pound = money value once based on weight• English still use “pound” for currency

– Ounce = romans divided pound into 12 units “unciae” • Later divided into 16 parts

So What’s the Problem?

• Problems arose with accuracy, consistency, fairness– All feet, hands, paces aren’t the same– All handfuls and heaps aren’t the same– Different countries had different measurements• Greeks divided their foot into 16 units• Romans divided their foot into 12 units

– Inch = Width of thumb– English used 3 barleycorns (seeds) to measure inch

So What’s the Answer?

• Problems arose with accuracy, consistency, fairness– Standards were established

• Standard: Agreed upon measurements that stay the same wherever you go

– Systems• System: measurements that are all related

– Customary System – based on body– Metric system – based on the Earth

• Most widely accepted standards in world

What is the metric system?

• Created in France 1793• Scientists based the system on a meter– Meter means “measure” – Distance from equator to North Pole /10,000,000

• Used all over the world• US is only major country not to use– E.C. What are the only other two countries not to

use metric system?• Based on 10s

Why the metric system?

• Scientists created and use the metric system– Science occurs all over the world – not just in USA– Scientists need to speak the same “language” when it

comes to measurements• We’re in science class

• The entire Earth (almost) uses the metric system– (The United States and two others)

• Business and trade uses metric system– Especially if they interact with foreign markets

Quiz

• Length:– How many inches in a foot– How many feet in a yard?– How many yards in a mile?– How many inches in a mile?

• Volume:– How many teaspoons in a tablespoon?– How many tablespoons in a cup?– How many cups in a gallon?

Quiz (continued)

• Mass:– How many ounces in a pound?– How many pounds in a ton?

• Temperature: – What is the freezing point of water?– What is the boiling point of water?

• Extra Credit: – What is a common equivalent for the following: (Choose 4)

• Fathom?• Chain?• Rod?• Furlong?• League?• Peck?

Extra Credit

• Extra Credit: – What is a common equivalent for the following:

(Choose 4)

• Fathom?• Chain?• Rod?• Furlong?• League?• Peck?

Race???

SI (Metric) 1.5 m 2.75 m 3.333 m+ 4.625 m-------------------

Customary (American) 1 1/2 ft 2 3/4 ft 3 1/3 ft+ 4 5/8 ft-------------------

And the Winner Is???

SI (Metric) 2 1 1.5 m 2.75 m 3.333 m+ 4.625 m------------------- 12.208

Customary (American) 2 1 1/2 ft = 1 12/24 2 3/4 ft = 2 18/24 3 1/3 ft = 3 8/24+ 4 5/8 ft = 4 15/24------------------- ------------------ (53/24 = 2 5/24) 10 53/24 (10 + 2 5/24 = 12 5/24) 12 5/24

Easier?

• The metric system is easier to use than our system– Only one base unit for each measurement• Prefixes help with very large/small measurements

– Based on 10’s• Decimals not fractions

– Faster– Very easy to add/subtract/multiply/divide

• Changing prefixes; just move decimal

Comparison

SI (Metric System)• Units from Earth• 1 unit with prefixes• Based on 10s• Decimals• Faster

Customary (American System )

• Units from body• Many units• Based on 2s, 3s, 4s, 8s, 12s,

16s, 36s, etc.• Fractions• Slower

Prefixes (mnemonic device)

• K• H• Da• M• D• C• M

Prefixes

• K• H• Da• M• D• C• M

• King• Harry• Decked• My• Dad’s• Creepy• Monster

Length• Base unit – meter – Meter stick or metric ruler

• Smaller – decimeter– 10 decimeters = 1 meter– 1 decimeter (10-20)(40-50)

• Smaller yet – centimeter– 10 centimeters = 1 decimeter– 1 centimeter (11-12)(47-48)

• Smallest – millimeter– 10 millimeters = 1 centimeter– 1 millimeter (distance between tiny tick marks)

Where do decimals come in?

• In between whole numbers – Between 4 and 5 cm– Write “4.”– Count the smaller unit (3 little tick marks)– Write the number after the decimal 4.3 cm

Changing Prefixes

• Based on 10s

• Example 1– 11.8 cm = ? mm– 11.8 cm x 10 mm = 11.8 x 10 = 118 mm 1 cm

• Example 2– 4.65 m = ? mm

Changing Prefixes

• Based on 10s

• Example 1– 11.8 cm = ? m– 11.8 cm x 1 dm x 1 m = 11.8 = 0.118 m 10 cm 10 dm 100

• Example 2– 4.65 m = ? km

Additional Examples

Length Summary

• Length: distance between two points• Instrument: metric ruler / meter stick• Base unit: meter (m)• Accuracy: – Start at the “0”– Count accurately– Meter sticks end to end– Measure in a straight line

Volume Summary

• Volume: amount of space an object takes up• Instrument: graduated cylinder• Base unit: liter (L)– 1 cm3 = 1 mL

• Accuracy: – Know what you are counting by 0.5s, 1’s, 5s, – Keep graduated cylinder on flat surface– Measure to bottom of meniscus– Read meniscus at eye level

Volume by Difference

• Measure volume of water– Easy to use number

• Add object to water• Measure volume of water and object• Subtract beginning volume from ending

volume

Mass Summary

• Mass: amount of matter in an object• Instrument: triple beam balance• Base unit: gram– 1 cm3 water = 1 mL = 1 gram– 1 L = 1 kg

• Accuracy: – “Zero” triple beam balance before measuring– Carefully set object on pan– Keep triple beam balance on flat surface

“Zero” Triple Beam Balance

• Clear off pan• Move all riders to “0”• Turn tare knob if pointer isn’t at “0”

Mass by Difference

• Find mass of an object• Change the object– Add to it – Take away from it

• Find the mass of the changed object• Subtract smaller mass from larger mass

Temperature Summary

• Temperature: amount of thermal (heat )energy in object

• Instrument: thermometer• Base unit: degree Celsius (°C)• Accuracy: – Know what you are counting by– Below “0” temperatures are “-”– Keep thermometer in middle of substance

Graph Summary

• X-axis: horizontal axis (bottom)– Plot independent variable• Independent variable: variable that you change / test

• Y-axis: vertical axis (side)– Plot dependent variable on• Dependent variable: variable that you

observe/measure

Graph Summary (continued)

• Set-up your graph– Label your axes with variables and units– Label your axes with numbers

• Determine maximum value for each variable• Count number of lines across & up and down• Choose an easy number to count by (1s, 2s, 5s, 10s)• Label only a few of the lines

– Plot points (across, then up)– Connect dots with line (trend line)– Add title (include both variables)

Safety

• Glassware:– Carry with two hands– Set it down carefully– Keep it in the middle of table

• Triple beam balances:– Carry with two hands– Set it down carefully– Keep it in the middle of the table

• Substances:– Don’t eat or drink (unless given permission)