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General Physical Science Introduction

General Physical Science Introduction. The following concepts will be addressed in this lecture: Units Scientific Notation Area and Volume Metric prefixes Significant figures Scientific Method. Two Systems. Science is concerned with making sense out of the physical environment

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General Physical Science Introduction

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  1. General Physical Science Introduction The following concepts will be addressed in this lecture: • Units • Scientific Notation • Area and Volume • Metric prefixes • Significant figures • Scientific Method

  2. Two Systems • Science is concerned with making sense out of the physical environment • Describe the properties (characteristics) of nature • Quantify (measure) these properties • What units should we use? http://en.wikipedia.org/wiki/History_of_measurement • Two sets of measurement systems are in use • English units (feet, pounds, seconds) • Based primarily on size of human body parts • Metric units (meter, kilogram, second) • Based on referents in nature • Established in 1791 during the Age of Reason

  3. Metric System • Three fundamental quantities • Length (meter) • Originally, the distance from equator to pole = 10 million meters • Today, 1 meter = distance traveled by light in 1/299,792,458 of a second • Mass (kilogram) • Originally, the mass of 1 liter of water • Now defined by the mass of a particular metal cylinder • Time (second) • Originally, 1/86,400 of a solar day • Now, the time for 9,192,631,770 vibrations of the Cs-133 atom • Prefixes are powers of ten

  4. Significant figures • We use the concept of significant figures every day, often without realizing it. • For example, how much does a Snickers bar cost? How about an ipod? A Toyota Prius? • $.50 (two sig figs) • $250 (two sig figs) • $21,000 (two sig figs) • How old are you? Ask a first grader and what do they say? • When we estimate ages of others, we tend to lose years for older people, choosing instead to say things like “early 40’s”, or “late 50’s”.

  5. Three rules • There are three rules on determining how many significant figures are in a number: • Non-zero digits are always significant. • Any zeros between two significant digits are significant. • A final zero or trailing zeros in the decimal portion ONLY are significant. • Note that sometimes zeros at the end really are significant. One way to express their significance is with a decimal point at the end. e.g. 10. years old; or 100. gallons • Click here for a tutorial on significant figures

  6. Exact numbers Exact numbers, such as the number of people in a room, have an infinite number of significant figures. Exact numbers are counting up how many of something are present, they are not measurements made with instruments. Another example is 1 foot = 12 inches. There are exactly 12 inches in one foot. Therefore, if a number is exact, it DOES NOT affect the accuracy of a calculation nor the precision of the expression. Some more examples: • There are 100 years in a century. • 2 molecules of hydrogen react with 1 molecule of oxygen to form 2 molecules of water. • There are 500 sheets of paper in one ream. • Interestingly, the speed of light is now a defined quantity. By definition, the value is 299,792,458 meters per second.

  7. Powers of ten • Scientific notation • A number between 1 and 10 multiplied by a power of 10, for example • Mass of Earth = 5.98 x 1024 kg, or 5,980,000,000,000,000,000,000,000 kg • Diameter of Atom = 2.5 x 10-10 m, or 0.00000000025 m • Notice how convenient powers of ten are for very large or very small numbers! • Positive and negative exponents • Large values will have positive exponents • Tiny values will have negative exponents

  8. Units • A number without a unit is virtually meaningless! • Numbers and units can be combined to make useful ratios. • E.g. The speed limit is 70 miles per hour, or 70mi / 1hr. • E.g. Timothy eats 3300 per day. • 3300 WHAT, you might ask? It could be 3300 twinkies, or sunflower seeds, or ants! The number is virtually meaningless without the unit. In this case, it should read 3300 Calories per day. • Units for area are ft2 or m2, or any other length squared • ***Although 1 m = 3.28 ft, 1 m2≠ 3.28 ft2 This is obvious in the scaled image at right! How many blue squares could fit within the red square? • 1 m2 = (3.28 ft)2 = 10.76 ft2 • Similarly, 1 m3 = (3.28 ft)3 = 35.3 ft3 • Here is a nice link: http://www.unit-conversion.info/area.html

  9. Metric Prefixes • Each metric prefix is a numeric value, and expressed as a power of ten • Giga (G) = 109 • Mega (M) = 106 • Kilo (k) = 103 • Hecto (h) = 102 • Deka (da) = 10 • Deci (d) = 10-1 • Centi (c) = 10-2 • Milli (m) = 10-3 • Micro () = 10-6 • Nano (n) = 10-9 • Pico (p) = 10-12 Example: Steven has $3,420 in his checking account. Express this amount in kilo-dollars, centi-dollars, and nano-dollars. Example: If the i-pod nano were really a nanometer thick, express its thickness in centimeters both as a numeric value and a power of ten. • The answer can be found this way: 1 nm (1cm / 1x107nm) = 1x10-7cm, or 0.0000001 cm • A more explicit way is to convert to the base unit, m, and then to cm: 1 nm (1m / 1x109nm) (1x102 cm / 1m) = 1x10-7cm, or 0.0000001 cm

  10. Ratios • Measurement information used to describe something is called data • Often we compare measurements by using ratios • An example of such a ratio is Density • Density = mass / volume • By looking at the density ratio, we can compare objects of different sizes • Often we compare the density ratio of one material to some very common material, such as water Example: Timothy finds a rock that is nearly a rectangular solid. He measures it to be 3cm by 6cm by 2cm. He then measures its mass rock’s mass as 350 grams. Calculate its density in g/cm3, kg/m3, and kg/Liter. Is it more or less dense than water?

  11. Scientific Method • The process by which scientific investigation proceeds • Basically, these items • Collecting observations • Developing explanations • Testing explanations • Developing explanations may involve theories or models • Testing explanations involves making predictions for the outcome of a specific experiment, and then doing the experiment to see what the actual outcome is • Something that cannot be tested, at least in theory, is not scientific • Lacking the technology to test a prediction today does not make it unscientific if we can at least conceive of some experiment that could test it (or some parts of it)

  12. Scientific Method • A hypothesis is a tentative thought- or experiment-derived explanation • An experiment is a re-creation of an event or occurrence in a way that enables a scientist to test a hypothesis • A controlledexperiment compares two situations in which all the influencing factors are identical except for one • A theory is a broad working hypothesis based on extensive experimental evidence. • A model is a description of a theory or idea that accounts for all known properties. • A scientifictheory is used for those explanations that have survived the test of detailed examination for long periods of time • The atomic theory describes the nature of atoms and molecules • A scientificlaw describes an important relationship that is observed in nature consistently time after time. • The law of gravity describes the mutual attraction of two masses separated by a distance

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