EA Notes (Scen 101), Tillery Chapter 1 What is Science? & How to Make Measurements Introduction This chapter first defines words that are used throughout Science. Then discusses: measurement systems how to make measurements. how scientists use the measurements And then defines a few terms important to ALL scientists. EA Lec Notes (Scen 101) Til 7 Ed-Chap1-1 - Printed 2/18/2008 11:16 AM
Objects, Concepts, Properties & Referents Object occupies space and usually you can see or touch. Concept is a generalized description, mental picture or idea. Generalized to apply to ANY object A Statement, math formula, or both. Example: Area = Length x Width A LW Properties describe specific characteristics of Objects or Concepts. Referents are used to help us understand the descriptions of properties. EXAMPLES: STATEMENT DESCRIBES REFERENT Text Book cover is flexible & white. The Area of the book is 2 9 in 11in 99 in. Object + Concept. Concept + Object. Implied by terms used. Square 1-inch on a side. Temperature is 72 F. Concept only. Known Temperature scale. EA Lec Notes (Scen 101) Til 7 Ed-Chap1-2 - Printed 2/18/2008 11:16 AM
Measuring Properties Measurement describes a property numerically. ( Definition ) Unit: A referent used for numerical measurement. ( Definition ) The Measurement Process: 1 Pick a unit suitable for the property being measured. 2 Count how many of these units (and fractional units) are needed. 3 Write or state the number AND the name of the unit. DEMO EXAMPLE: Measure the length of this Text Book. For a Unit to be useful, it size must be some Standard that can be maintained AND reproduced easily. STANDARD Measurement Systems English System: the oldest of the systems still in use. Metric Systems (3): 2 established in 1791. (1 modified in 1960.) "Metric" Is Defined as unit size conversion by powers of 10. EA Lec Notes (Scen 101) Til 7 Ed-Chap1-3 - Printed 2/18/2008 11:16 AM
Fundamental Properties Fundamental Properties are Basic Concepts. They Can't be defined in terms of others. The Building Blocks used to define and describe other Concepts & Objects. Physics requires only FOUR to describe ALL its concepts. Length measures the straight-line distance between any 2 points in space. Often in 3 dimensions. Mass measures the quantity of matter in an object. (Better definition in Chapter 2). Time measures the (forward) flowing of events. Charge (Electric) Further discussion in Chapter 6. A System of Basic Units is a set of standards for each Fundamental Property. EA Lec Notes (Scen 101) Til 7 Ed-Chap1-4 - Printed 2/18/2008 11:16 AM
Basic (Standard) Units of the Metric Systems Three different systems are in use today. Fundamental Property mks Unit [abbrev] SI Unit [abbrev] cgs Unit [abbrev] length meter [m] meter [m] centimeter [cm] mass kilogram [kg] kilogram [kg] gram [g] time second [s] second [s] second [s] elec. charge Coulomb [C] not used in course elec. current Ampere [A] not used in course We'll use mostly mks in this course. The scientifically preferred system, the SI, was adopted in 1960. The difference here is in the basic electrical units (see table). The cgs system is frequently used because its base units are a handy size (lab experiments, for example.) EA Lec Notes (Scen 101) Til 7 Ed-Chap1-5 - Printed 2/18/2008 11:16 AM
Metric Prefixes The metric prefixes are letters (roman or greek) that go in front of the main unit to multiply its size by a power of 10. All of these are listed in T.1.3, and those we'll use are copied onto the back of our first Formula Sheet. You can cross out Hecto, Deka, and Deci. They're rarely used. Don't confuse Mega [M] with Milli [m]. Original 1791 Standard for gram & The Liter 1 gram was defined as mass of 1 cm 3 of water at 4 C. For LIQUID VOLUME measure, 1 Liter was defined as = 1000 cm3. Thus 1 Liter of water has a mass of 1000 g = 1 kg. For smaller liquid volumes, 1 ml =.001 L =.001 x 1000 cm3 = 1 cm3 EA Lec Notes (Scen 101) Til 7 Ed-Chap1-6 - Printed 2/18/2008 11:16 AM
Understandings from Measurements Data Data is measured information used to describe a quantity. It MUST have BOTH the number AND the name of the unit. Relationship A Concept showing a connection among different types data. Is expressed verbally, with an equation, or with a graph (see page 12 these notes). Ratio One quantity divided by a second quantity. Used to describe MANY Concepts (or Relationships). EA Lec Notes (Scen 101) Til 7 Ed-Chap1-7 - Printed 2/18/2008 11:16 AM
Density (a Ratio Example) Mass Density is a concept defined as the ratio of a object's mass to it's volume. In other words: Mass Density equals Mass divided by Volume For an object made COMPLETELY of ONE kind of material, the density depends ONLY on the material, (as in T.1.4, p.10.) It's a MATERIAL PROPERTY. Using just words to define concepts or relationships is cumbersome. We need "shorthand" methods that use SYMBOLS: EA Lec Notes (Scen 101) Til 7 Ed-Chap1-8 - Printed 2/18/2008 11:16 AM
Symbols In Equations and Proportions Used to shorten concept or relationship definitions (such as for density). Symbols: Shapes used to represent Quantities or Operations. Quantities (2 Types): are Measured properties or concepts. Variables: Quantities expected to change with time. (Example: Density, Mass, Volume.) Constants, Numerical or Physical: never change. Quantity Symbols: Most Fixed by agreement: ( [or d], m, V). Operations: relationships between Quantities. (equals, divided by [or ratio of].) Operation Symbols: All Fixed by agreement: (=, / or ). Equation: Symbols show the relationship between Quantities. m V BOTH the Numbers AND the Units must be (or REDUCE to) the same on both sides of the equation, or else it's wrong. EA Lec Notes (Scen 101) Til 7 Ed-Chap1-9 - Printed 2/18/2008 11:16 AM
Problem Solving Step 1: Step 2: Step 3: Step 4: Step 5: Step 6: Step 7: Read problem. Maybe sketch? write givens and unknown(s). Identify Principles. Find equation(s). Solve for unknown alone on the left. Check consistent units. Convert? units if necessary. Substitute numbers and units. Do the math on numbers and units separately. Box the answer. Do Ex. B-5, p.27. EA Lec Notes (Scen 101) Til 7 Ed-Chap1-10 - Printed 2/18/2008 11:16 AM
Ex. B-5, p.27. m 51. 5 g V 50. 0 cm? m V 51. 5 g 50. 0 cm 1. 03 3 g cm 3 3 ; Seawater EA Lec Notes (Scen 101) Til 7 Ed-Chap1-11 - Printed 2/18/2008 11:16 AM
Proportion: (An important way to Understand Measured Data) Numbers and their units NEED NOT be the same on both sides. Direct Proportion: m V (for a specific material) Proportionality Constant: correct units to do so, m converts a proportion into an equation. Needs V Inverse Proportion: 1 (for a fixed mass of gas) V Graphs are used to describe Proportions and Relationships. In the labs we'll do, all relationships will be Straight-Line-Graphs. You'll calculate the SLOPE of the line, which = the proportionality constant of the equation describing the relationship. In all lab reports you MUST use MY method of calculating slope, an improvement on the method shown in text-book Appendix A-8 and lab-book Appendix II. This improvement, part of the Math Review, is both less work to do and more accurate. EA Lec Notes (Scen 101) Til 7 Ed-Chap1-12 - Printed 2/18/2008 11:16 AM
The Nature of Science Scientific Method: 1 Observe and Record Facts and Data 2 Propose Explanation. (WHY and HOW.) Sometimes GUESS Why or How. Determine Consequences of Guess. Compare to observed data. Improve Guess, if needed. The most important steps for Modern Science are: 3 Make Many New Predictions using Explanation. Experimentally Test Truth of New Predictions. 4 Dispose, MODIFY, or Confirm Explanation. These require Good, Reproducible Measurements EA Lec Notes (Scen 101) Til 7 Ed-Chap1-13 - Printed 2/18/2008 11:16 AM
Natural Philosophers: Until 500 years ago, scientific measurement tools were crude. Scientific progress was by Natural Philosophers, who looked at facts, proposed explanations, but made no new predictions. Today's important steps weren't done. (Aristotle) Investigations, Data, and Explanations Data is recorded measurements. The following are important: Reliability: How reproducible over many trials. Precision: Instrument's smallest possible measurement. (least count) Explanations of why things happen. Hypothesis: Tentative explanation (early stages). Principles and Laws: Hypotheses tested many times by Controlled Experiments. EA Lec Notes (Scen 101) Til 7 Ed-Chap1-14 - Printed 2/18/2008 11:16 AM
Models and Theories Model: Uses analogies to help explain things that can't be seen. [Model of Solid below (text p.99)] Models can be either physical (real), mental, or equation. Theory: A broad, detailed explanation that guides scientists' thinking. An underlying goal of science is to develop and improve theories. EA Lec Notes (Scen 101) Til 7 Ed-Chap1-15 - Printed 2/18/2008 11:16 AM