Chapter 1: The Science of Physics. Physics 1-2 Mr. Chumbley

Transcription

1 Chapter 1: The Science of Physics Physics 1-2 Mr. Chumbley

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3 The Topics of Physics The origin of the word physics comes from the ancient Greek word phusika meaning natural things The types of fields of physics vary from the very small to the very large While some physics principles often seem removed from daily life, those same laws those same laws describe everyday events as well

4 Areas of Physics Name Subjects Examples Mechanics motion, interactions between objects falling objects, friction, weight, moving objects Thermodynamics heat and temperature melting and freezing processes, engines, refrigerators Wave Mechanics specific types of repetitive motion springs, pendulums, sound Optics light mirrors, lenses, color Electromagnetism electricity, magnetism, light electrical charge, circuitry, permanent magnets, electromagnets Relativity Particles moving at speed, generally very high speed particle accelerators and collisions, nuclear energy Quantum Mechanics Behavior of subatomic particles the atom and its parts

5 What is Physics? How can physics be defined if it so many different things? Physics can be defined as: The study of matter, energy, and the interactions between them This definition is basic yet very broad

6 The Scientific Method All scientific studies begin with a question There is no single procedure all scientists follow The scientific method is a set of steps that is common to most high quality scientific investigations

7 Using Models to Describe Phenomena The physical world is very complex In order to simplify the world, physicists construct models to isolate and explain the most fundamental aspects of a phenomenon A model is a pattern, plan or description designed to show the structure or workings of an object, system, or concept Models come in a variety of forms

8 Using Models to Describe Phenomena In order to simplify the model, only the relevant components are considered part of the system A system is a set of particles or interacting components considered to be a distinct physical entity for the purpose of study Components not considered part of the system can generally be considered to have little to no impact on the model

9 Models and Experimentation Models are extremely beneficial in helping to design experiments Once a phenomenon has been identified, a hypothesis can be formed A hypothesis is an explanation that is based on prior scientific research or observations and that can be tested By creating a model of the phenomenon, the necessary factors for designing an experiment can be identified

10 Models and Experimentation A model helps to ensure that controlled experiments are set up A controlled experiment is an experiment that tests only one factor at a time by using a comparison of a control group with an experimental group

11 Models and Predictions Once a model has been tested and supported repeatedly, that model can then be used to make predictions of future events The best scientific models are used to predict outcomes in different scenarios that are different than the initial system

12 Homework Read Chapter 1, Section 1: What is Physics? Answer #1-5 of the Formative Assessment Questions on p. 9

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14 What Can a Measurement Tell You? Often times we look at measurements as simple values, yet these values are different than simple numbers A measurement tells dimension, the kind of physical quantity A measurement tell the magnitude of the physical quantity A measurement tells the unit by which the physical quantity is expressed

15 Standard System of Measurement In 1960, an international committee agreed upon the Système International d Unités (SI) for scientific measurements The most common basic units of measure are: Unit Symbol Dimension meter m length kilogram kg mass second s time Original Standard One ten-millionth distance from equator to pole Mass of cubic meters of water average solar days Current Standard Distance traveled by light in a vacuum in s Mass of a specific platinumiridium alloy cylinder 9,192,631,770 times the period of a radio wave emitted from a cesium-133 atom

16 Standard System of Measurement Not every dimension can be described using just one of these units Derived units are formed when units are combined with multiplication and division Units help to identify the type of quantity being observed or measured

17 SI Prefixes Smaller than base unit Prefix Power Abbreviation yocto y zepto z atto a femto f pico 1o -12 p nano 10-9 n micro 10-6 µ milli 10-3 m centi 10-2 c deci 10-1 d Larger than base unit Prefix Power Abbreviation deka 10 1 da hecto 10 2 h kilo 10 3 k mega 10 6 M giga 10 9 G tera T peta P exa E zetta Z yotta y

18 Using SI Prefixes The advantage of using SI and its prefixes is that it can put numbers into understandable values Converting between one unit to another is simply a matter of moving the decimal

19 SI Conversions To convert between one unit and another we use a conversion factor Conversion factors are built from any equivalent relationship The value of a conversion factor is always equal to 1 Desired unit for conversion is opposite the location of the original unit

20 SI Conversions Example #1: Convert 37.2 mm to m. Conversion factor for mm to m is: 10 3 m 1 mm 37.2 mm 10 3 m 1 mm = m

21 Scientific Notation Scientific notation is a way of expressing numbers consistently The format for scientific notation is a value, called the significand, that is expressed as a value with a single digit left of the decimal point multiplied by a power of 10 For example 112 =

22 Practice! Find a partner nearby Complete the Practice problems on page 15, #1-5

23 Homework Chapter 1 Review p Complete # 5, 8, 10, 11, 12, 13

24 Accuracy and Precision Accuracy A description of how close a measurement is to the correct or accepted value of the quantity measured Precision The degree of exactness of a measurement

25 Uncertainty and Error Uncertainty is the measure of confidence in a measurement or result Uncertainty can arise from a variety of sources of error Method error occurs when measurements are made using inconsistent instruments, techniques, or procedures Instrument error occurs when the tools used to take measurements have flaws

26 Precision and Instruments The exactness of a measurement is often times dependant upon the tool used When taking measurements with a tool, the precision of that tool is the smallest marked measurement Precision can often times be improved by making an estimation of one additional digit While an estimated digit carries a level of uncertainty, it still provides greater precision

27 Significant Figures One way we indicate precision in measurement is through significant figures Significant figures are those digits in a measurement that are known with certainty plus the first digit that is uncertain

28 Measurements and Significant Figures The uncertain digit in a value comes directly from the measurement Generally, the last digit recorded is an estimated digit that comes directly from an estimation in the measurement

29 Significant Figures and Scientific Notation When the last digit in a measurement is zero, there can be confusion concerning the value In this situation, using scientific notation can add additional clarity since scientific notation includes all significant figures

30 Rules for Determining Significant Figures (Figure 2.9 on page 18) Rule 1. Zeroes between other nonzero digits are significant. 2. Zeroes in front of nonzero digits are not significant. 3. Zeroes that are at the end of a number and also to the right of the decimal are significant. 4. Zeroes at the end of a number but to the left of the decimal are significant if they have been measured or are the first estimated digit; otherwise, they are not significant. Example 50.3 m has three significant figures s has five significant figures kg has three significant figures ms has one significant figure g has four significant figures kg has seven significant figures 1000 m has one significant figure 1030 s has three significant figures

31 Rules for Calculating with Significant Figures (Figure 2.10 on page 19) Type of Calculation Addition or Subtraction Multiplication or Division Rule Given that addition and subtraction take place in columns, round the final answer to the first column from the left containing an estimated digit The final answer has the same number of significant figures as the measurement having the smallest number of significant figures Example round round 658

32 Calculators and Calculations Calculators do not take into account significant figures While the calculator can give you the value of a calculation, determining the number of significant figures is done manually When rounding occurs multiple times within a calculation, there can be significant error Generally, it is better to carry extra non-significant digits in calculations and round the answer to the appropriate number of significant digits at the very end

33 Rules for Rounding in Calculations (Figure 2.11 on page 20) What to do When to do it Example (3 SF) Round down Round up Whenever the digit following the last significant figure is 0, 1, 2, 3, or 4 If the last significant figure is an even number and the next digit is a 5, with no other nonzero digits Whenever the last significant figure is 6, 7, 8, or 9 If the digit following the last significant digit is a 5 followed by a nonzero digit If the last significant figure is an odd number and the next digit is a 5, with no other nonzero digits becomes becomes becomes becomes becomes becomes becomes 79.4

34 SI Conversions Converting between an SI units of the same dimension is very simple: just move the decimal The number of times the decimal is moved is equal to the difference between the powers of 10 The smaller the unit, the larger the value of the measurement The larger the unit, the smaller the value of the measurement

35 SI Ladder

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37 Mathematics and Physics In physics, the tools of mathematics is used to analyze and summarize observations This can be in a variety of forms, most commonly tables, graphs, and equations

38 Tables Tables are a convenient way to organize data Having data organized in a table allows for easier use for comparison or calculation All tables and data should be clearly and appropriately labeled Data Table: Time and Distance of Dropped-Ball Experiment Time (s) Distance golf ball falls (cm) Distance tabletennis ball falls (cm)

39 Distance (cm) Graphs Distance (cm) as a function of Time(s) Constructing graphs can help to identify relationships or patterns The relationships described in graphs can often times be put into equations Time (s)

40 Equations In mathematics equations are used to describe relationships between variables In physics, equations serve as tools to describe the measurable relationships between physical quantities in a situation

41 Equations and Variables Generally, scientists strive to make equations as simple as possible To do this scientists use different operators and variables in place of words: y = 4.9( t) 2 Quantity Symbol Units Unit Abbreviation Change in vertical position Δy meters m Change in time Δt seconds s Mass m kilograms kg Sum of all forces ΣF newtons N

42 Dimensional Analysis Dimensional analysis is a procedure that can be used to determine the validity of equations Since equations treat measurable dimensions as algebraic quantities, mathematical manipulations can be performed

43 Order of Magnitude Dimensional analysis can also be used to check answers Using basic estimation to a power of 10, simple calculations can be made to determine the relative scale of the answer

44 Derived Units with Dimensional Analysis Similar to converting between base units in SI, conversions of derived units is sometimes necessary When this happens, each portion of the derived unit needs to be converted