Physical Science Lecture 2 Instructor: John H. Hamilton

Lecture overview Units Systems of units SI units Specific units: length, volume, mass, temperature Recommended assignments

Units What units are and why they are crucial – A definite magnitude (quantity) of a physical quantity adopted by convention that is used as a standard of measurement of the same physical quantity – Crucial so that we have consistent measurements Common systems of measurements – US customary (formally the “English system”) – SI (system International) formally “metric” Fundamental and derived units – Fundamental units cannot be broken down or reduced – Derived units are combinations of fundamental units

Fundamental and derived units Fundamental units (SI) – Length –Meter-m – Mass- kilogram-kg – Luminous intensity- candela – Time- Second- s – Electric current-Ampere-A – Temperature-Kelvin-K – Amount of a substance-Mole-mol Derived units – Everything else! Ex speed-m/s

SI vs USCS USCS “English” – Arbitrarily based on some measurement Inch= width of kings thumb Foot=Length of kings foot – Not a good relationship between measurements No real relationship between units derived from fundamental units- example gallons to cubic feet SI system – Based on internationally accepted standards – Good relationship between most units. liter = cubic decimeter – Base 10 – Makes calculations much easier!

Scientific notation Scientific notation is a means of writing numbers that scientist and some others use – It involves writing the significant digits of the number multiplied by 10 raised to some exponent – 4.5x10 3 people is an example of writing a population in scientific notation

Significant digits The concept of significant digits is a crucial concept. The number of significant digits in a number tell us the number that is actually known – For example if we say a country has a population of 40 million people the actually number of people could be anywhere from 39.5 million to 40.5 million. When we wrote 40 million people we wrote TWO significant digits. When we wrote 39.5 million we wrote THREE significant digits – It is important to only write the significant digits that we know Examples (for numbers with magnitudes greater than 1) – 458 has 3 significant figures – 4 million has 1 significant figure – 4,000,000 has 6 significant figures Examples (for numbers with magnitudes less than 1) – 0.01 has 1 significant figure – has 2 significant figures

Writing in scientific notation Remember it is the number of significant digits multiplied by 10 raised to the appropriate exponent – Write 3.8 million in scientific notation 3.8x10 6 – Write 567 thousandths in scientific notation 5.67x10 -1 I did not write 567 X I used a normalized scientific notation. The significant digit portion is kept between 1 and 10

Prefixes in SI

Some relationships between SI units Length and volume: Length is a fundamental unit while volume is a derived unit – Volume is the amount of space something occupies – 1 liter (l)= 1 cubic decimeter (dm 3 ) – 1 ml=1 cubic centimeter (cc)

Length-volume relationship

Mass in SI units Mass- describes how much matter there is in something – In SI the unit is a kg – Compares to 2.2 lbm – 1cm 3 of water has a mass of one gram

Temperature Will define temperature later, for know your understanding of it is enough – Scientist use Kelvin (K) for temperature. It begins at absolute zero – Each difference in degree in kelvin is the same as a difference in degrees Celsius – Absolute zero is 273 degrees C below zero – Water freezes at 0C but at 273 K – Water boils at 100C but at 373K

Lecture Review Units and why they are important SI system Significant digits Relationship between volume and length Mass and temperature in SI

Recommended Assignments Obtain one or more kitchen measuring cups. From this find three find the volumes that correspond to 250 ml and 500 ml. convert those liters and to cubic meters. Write the answers in scientific notation Estimate (this means do your best to find the lengths needed) the volume of your bedroom. If a swimming pool where 3m deep 20m long and 10 m wide. What would be the mass of water in the pool A long time ago measurements where based on arbitrary things like the length of a kings foot. How would you go about convincing people of that time they needed a better standard. Explain this to someone and ask them to ask you questions about it Discuss in a paragraph the benefits of the SI system over the old English system