Chapter 1: The Science of Physics

Physics 1-2 Mr. Chumbley

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

Areas of Physics

Name

Mechanics Thermodynamics Wave Mechanics Optics Electromagnetism Relativity Quantum Mechanics

Subjects

motion, interactions between objects heat and temperature

Examples

falling objects, friction, weight, moving objects melting and freezing processes, engines, refrigerators springs, pendulums, sound specific types of repetitive motion light electricity, magnetism, light Particles moving at speed, generally very high speed Behavior of subatomic particles mirrors, lenses, color electrical charge, circuitry, permanent magnets, electromagnets particle accelerators and collisions, nuclear energy the atom and its parts

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

The Scientific Method •

All scientific studies begin with a question

•

There is no single procedure all scientists follow

•

The

scientific method

common to most high quality scientific investigations is a set of steps that is

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

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

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

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

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

Homework •

Read Chapter 1, Section 1: What is Physics?

•

Answer #1-5 of the Formative Assessment Questions on p. 9

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

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

meter kilogram second

Symbol

m kg s

Dimension

length mass time

Original Standard

One ten-millionth distance from equator to pole Mass of 0.001 cubic meters of water

Current Standard

Distance traveled by light in a vacuum in 3.33564095 × 10 -9 s Mass of a specific platinum iridium alloy cylinder 0.000011574 average solar days 9,192,631,770 times the period of a radio wave emitted from a cesium-133 atom

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

SI Prefixes

Smaller than base unit Prefix

yocto zepto atto femto pico nano micro milli centi deci

Power

10 -9 10 -6 10 -3 10 -2 10 -1 10 -24 10 -21 10 -18 10 -15 1o -12

Abbreviation

n µ m c d y z a f p

Larger than base unit Prefix

deka hecto kilo mega giga tera peta exa zetta yotta

Power

10 1 10 2 10 3 10 6 10 9 10 12 10 15 10 18 10 21 10 24

Abbreviation

da h k M G T P E Z y

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

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

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 = 3.72 × 10 −2 m 1 mm

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

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For example 112 = 1.12 × 10 2

Practice!

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Find a partner nearby

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Complete the Practice problems on page 15, #1-5

Homework •

Chapter 1 Review p. 27-28

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Complete # 5, 8, 10, 11, 12, 13

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

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 procedures occurs when measurements are made using inconsistent instruments, techniques, or • Instrument error occurs when the tools used to take measurements have flaws

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

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

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

Rules for Determining Significant Figures

(Figure 2.9 on page 18)

Rule Example

1. Zeroes between other nonzero digits are significant.

2. Zeroes in front of nonzero digits are not significant.

50.3 m has three significant figures 3.0025 s has five significant figures 0.892 kg has three significant figures 0.0008 ms has one significant figure 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.

57.00 g has four significant figures 2.000 000 kg has seven significant figures 1000 m has one significant figure 1030 s has three significant figures

Rules for Calculating with Significant Figures

(Figure 2.10 on page 19)

Type of Calculation Rule Example

Addition or Subtraction Multiplication or Division 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 97. 3 + 5. 8 5 103. 1 5 round 123 × 5.35

658.05

round 103. 2 658

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

Rules for Rounding in Calculations

(Figure 2.11 on page 20)

What to do

Round down Round up

When to do it

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

Example (3 SF)

30.24 becomes 30.2

32.25 becomes 32.2

32.650 00 becomes 32.6

22.49 becomes 22.5

54.7511 becomes 54.8

54.75 becomes 54.8

79.3500 becomes 79.4

Homework •

Section 2: Formative Assessment (p 20) ▫ #3 and #4

•

Chapter 1 Review (p 28) ▫ #16, 20, 22

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

Tables

• • Having data organized in a table allows for easier use for comparison or calculation • Tables are a convenient way to organize data All tables and data should be clearly and appropriately labeled Data Table: Time and Distance of Dropped-Ball Experiment

Time (s)

0.000

0.067

0.133

0.200

0.267

0.333

0.400

Distance golf ball falls (cm)

0.00

2.20

8.67

19.60

34.93

54.34

78.40

Distance table tennis ball falls (cm)

0.00

2.20

8.67

19.59

34.92

54.33

78.39

Graphs

90 80 70 60 50 40 30 20 10 0 0

Distance (cm) as a function of Time(s)

0,1 0,2 0,3

Time (s)

0,4 0,5 • Constructing graphs can help to identify relationships or patterns • The relationships described in graphs can often times be put into equations

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

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

Change in vertical position Change in time Mass Sum of all forces

Symbol

Δy Δt

m

ΣF

Units

meters seconds kilograms newtons

Unit Abbreviation

m s kg N

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

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

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