The Science of Physics
Chapter 1
Chapter Overview
● Section 1
● Nature of physics and its related fields
● Scientific method of inquiry
● Role of models
● Section 2
● Basic SI units
● Precision vs. accuracy
● Scientific notation
● Significant digits
● Section 3
● Various ways of summarizing data
● Dimensional analysis
● Estimation procedures
Section 1.1 What is Physics?
●
Identify activities and fields that involve the
major areas within physics
●
Describe the processes of the scientific method
●
Describe the role of models and diagrams in
physics
1.1 What is Physics?
●
The study of the physical world
Use a small number of basic concepts, equations,
●
and assumptions to describe the physical world
●
Can be used to make predictions about a broad
range of phenomena
●
Appliances, tools, buildings, inventions are all
basic physics principles put to test
Electromagnetism –
Battery, starter,
headlights
Physics
Thermodynamics – Efficient
engines, use of coolants
Optics – Headlights,
rearview mirrors
Mechanics – spinning
motion of the wheels,
tires that provide enough
friction or traction
Vibrations and
mechanical waves –
Shock absorbers,
radio speakers,
sound insulation
Physics is Everywhere
When you buy ice cream, why do you put it in
the freezer when you get home?
●**Any problem that deals with temperature,
size, motion, position, shape, or color involves
physics**
●
There are major areas of physics that deal with
each of these
●
Physics is Everywhere
Areas Within Physics
Name
Subjects
Examples
Mechanics
Motion and its causes
Falling objects, friction, weight,
spinning objects
Thermodynamics
Heat and temperature
Melting and freezing processes,
engines, refrigerators
Vibrations and wave
phenomena
Specific types of repetitive
motions
Springs, pendulums, sound
Optics
Light
Mirrors, lenses, color, astronomy
Electromagnetism
Electricity, magnetism, light
Electrical charge, circuitry,
permanent magnets, electromagnets
Relativity
Particles moving at any speed,
including high speeds
Particle collision, particle
accelerators, nuclear energy
Quantum mechanics
Behavior of submicroscopic
particles
The atom and its parts
Physics is Everywhere
●
Sailboats
Design, build, and operate
●
Best shape so that is remains stable and floating, yet
●
quick and maneuverable
Knowledge of fluids
●
Efficient shape for sails and how to arrange them
●
Understanding motion and its causes
●
●Balancing
loads
So port isn't heavier than starboard
●
Knowledge on how the keel keeps the boat moving in
●
The Scientific Method
No single procedure is always taken in an
experiment
●
Certain common steps in all good scientific
investigations
●
The Scientific Method
The Scientific Method
●
There was a car accident and the police were
investigating… use the scientific method:
Observations/Data:
●
Hypothesis:
●
Experiments/Tests:
●
Interpret/Revise Hypothesis:
●
Conclusion:
●
Models
Simple models are often used to explain the
most fundamental features of various
phenomena
●Common technique
●
Break an event down into different parts
●
Use a model for each section
●
WE WILL
ALWAYS
DRAW
MODELS!!!!!!
Model
●
Observations
Ball’s size, spin, weight, color, surroundings, time in
the air, speed, and sound when hitting ground
●
●
First step
Identify the system
●
A single object and the items immediately affecting it
●
Ball and its motion
●
●
Disregard any characteristics that don't matter
Color, sound when hitting the ground
●
In some studies of motion, even size and spin are
disregarded
●
Models Help Build Hypothesis
●A hypothesis is a
reasonable explanation for
observations
●Can be tested with
additional experiments
●Modeling a
situation can help
identify variables as
well
●Galileo’s ‘thought
experiment’
Models Help Guide Experiments
●
Galileo performed many experiments
Observing weight only
●
Used same size objects, just different weight
●
No way to eliminate air resistance
●
●
Used rolling ball down smooth ramps as a
model
The steeper the ramp, the closer the
●
Experiments
●
Must deal with variables
Majority of the time a controlled experiment
●
Only one variable changed at a time
●
●
Galileo
Hypothesis to Prediction
●Until the invention of the air pump, it was impossible to
perform direct tests in the absence of air resistance
●Reasonably accurate predictions were still made
●Experiments are run until results match each other and
are in agreement with the hypothesis
●If not there could be error
●Then the hypothesis must be revised
Conclusions
●
Conclusions
Are only valid if they can be duplicated and verified
by other people under the same conditions
●
Research
●
Not only so scientists conduct experiments to
test hypothesis
They also RESEARCH!!!
●
Steps to doing scientific research
●
1.
Identifying reliable resources
2.
Searching the sources to find references
3.
Checking carefully for opposing views
4.
Documenting sources
5.
Presenting findings to other scientists for review and
discussion
Section 1.2 Measurements In
Experiments
●
List basic SI units and the quantities they
describe
●
Convert measurements into scientific notation
●
Distinguish between accuracy and precision
●
Use significant figures in measurements and
calculations
Numbers as Measurements
●
When in physics numbers will never stand alone
7
●
Means absolutely nothing
●
●
Must have units following the number
(anything labeled without units will be wrong) ☺
●
●
Length, mass, time, or something else?
If length: inches, centimeters, kilometers, light-
●
Numbers as Measurements
●
The units helps tell us what kind of physical
quantity being measured
Dimension
●
Basic dimensions – length, mass, time
●
●
There are many other dimensions as well
Force, velocity, energy, volume, and acceleration
●
All combinations of length, mass, and time
●
SI
SI is the standard measurement system for
science
●
Scientists like to use the same system of units for
measurement
●
If not that would be a lot of converting ☹
●
7 base units that each describe a single
dimension
●
Length – meters (m)
●Mass – grams (g)
●Time – seconds (s)
●
SI Prefixes
A very wide range of measurements will be
used
●
100,000,000,000,000,000 m for distances between
stars
●.000 000 001 m distances between atoms in a solid
●
●
Can deal with powers of ten
1x1017m
●1x10-9m
●
●
Prefixes to go with the powers
*MEMORIZE*
Conversions
●
Using SI, with the prefixes and same base
Conversion factors will always
=1
-
●
3
=
=
Any measurement multiplied by a fraction will be
●
multiplied by 1
The number and unit will change but the quantity
●
Dimensional Analysis
Mathematical techniques that uses
conversion factors to convert from one unit to
another
●
Dimensional Analysis
A typical bacterium has a mass of about 2.0μg.
Express this in terms of grams and kilograms.
●
Problem
The mass of an average person is 60,000,000
mg. Express this in grams and kilograms.
●
Dimension and Units Must Agree
Can’t measure a length then label in kilograms
(kg)
●
Must make sure use correct unit
●
●
We will ALWAYS use metric!!
No inches, feet, miles, lbs, tons
●
Accuracy and Precision
●
Accuracy
The closeness of measurements to the correct or
accepted value
●
●
Precision
Closeness of a set of measurements of the same
quantity made in the same way
●
Accuracy and Precision
Accepted Value = 55 km/h
Trial #1
Trial #2
Trial #3
Trial #4
Speed #1
50 km/h
53 km/h
60 km/h
57 km/h
Accurate but
not precise
Speed #2
53 km/h
57 km/h
58 km/h
54 km/h
Precise but
not accurate
Speed #3
55 km/h
55 km/h
55 km/h
55 km/h
Accurate and
precise
Problems with Accuracy are Due to
Error
●
Experimental work is never free of error
Important to minimize as much as possible
●
●
Should never have human error
Mistake in reading measurement
●
Mistake in recording results
●
Method should always be the same
●
Same instrument
●
Precision of Instrument
Poor accuracy can be corrected
●Precision based on the instrument
●
Instruments can only be so precise
●
Precise to the .1
Estimate the last place
13.65 cm
Significant Figures
●
Measurement that consists of all known digits
with an uncertain digit at the end
Uncertain digit
●
The digit that you as the experimenter must estimate
●
●
All digits are significant, but not necessarily
certain
●
Insignificant digits are never reported
●
YOU WILL ALWAYS NEED TO USE SIGNIFICANT
Sig Fig Rules
Sample Problems
●
How many significant figures?
●
28.6g
●
3440. cm
●
910m
●
.04604L
●
.067000kg
Rounding
●
Always round to significant figures
If adding 2 numbers with 3 significant figures each
●
Answer will have 3 significant figures
●
●
Use normal rounding
5 and up – round up
●
4 and down – stay the same
●
Sig Fig Math
●
Adding and Subtracting
Answer must have the same number of digits to
the right of the decimal point as there are in the
measurement having the fewest digits to the right
of the decimal point.
●2.59 + 6.8974 = 9.49
●
●
Multiplying and Dividing
Answer can have no more significant figures than
are in the measurement with the fewest number of
significant figures.
●3.05/8.47 = .360
●
Practice Problems
●
5.44m – 2.6103m =
●
2.4g/mL x 15.82 mL =
Conversion Factors and Sig Figs
Because a measurement is considered exact,
after conversion there is no rounding
●
Section 1.3 The Language of Physics
●
Interpret data in tables and graphs, and
recognize equations that summarize data
●
Distinguish between conventions for
abbreviating units and quantities
●
Use dimensional analysis to check the validity
of expressions
●
Perform order of magnitude calculations
Mathematics and Physics
Tools are used to summarize and analyze data
and observations
●
Often times mathematical relationships
●
In forms of charts and graphs
●
Data from Dropped-Ball Experiment
Time (s)
Distance Golf Ball Falls (cm) Distance Table Tennis Ball Falls (cm)
.067
2.20
2.20
.133
8.67
8.67
.200
19.60
19.59
.267
34.93
34.92
.333
54.34
54.33
.400
78.40
79.39
Mathematics and Physics
Graph
●
Provides a visual of time versus distance
Can determine distance traveled at any time
●
Through this equation
●
(change in position m) = 4.9 x (time of fall s)2
●
How far would the ball have fallen at .500 s?
Equations Indicate Relationships
●
Equations show how two or more variables are
related
Many equations do not have numbers
●
But symbols representing physical constants
●
●Δ
means difference or change in
Usually final minus initial
●
●
Units should help with equations
Units must cancel correctly
●
Units or Variables?
●
Variables are usually boldface
Stand for a measurement with specific units
●
Always check the context of the problem
●
Find the mass of something
●
Mass is variable m, units would be g or kg
●
●
Examples of Variables
Δx, Δy, Δt, c, m, a, v
●
●
Examples of Units
Dimensional Analysis
●
Use to check validity of equations
A car is moving at a speed of 88 km/h and has
●
traveled 725 km, how long did this trip take?