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Chapter 1 - The Science of PhysicsSection 1.1 - What is Physics?
What is Physics?Physics is the study of the physical world
Goal:To use a small number of basic concepts, equations, and assumptions to describe the physical world
Physics is EVERYWHERE!!
The atom and its partsBehavior of submicroscopic particles
Quantum mechanics
Particle collisions, particle accelerators, nuclear energy
Particles moving at any speed, including very high speeds
Relativity
Electrical charge, circuitry, permanent magnets . . .
Electricity, magnetism, and light
Electromagnetism
Mirrors, lenses, color, astronomy
LightOptics
Springs, pendulums, soundSpecific types of repetitive motions
Vibrations and wave phenomena
Melting and freezing processes, engines . . .
Heat and temperatureThermodynamics
Falling objects, friction, weight, spinning objects
Motion and its causesMechanics
ExamplesSubjectsName
Areas within Physics
Topics of Physics
Topics of Physics
The scientific Method
SCIENTIFICALLYPROVENX
Make observationsAnd collect data thatLead to a question
Formulate Hypothesis
Test Hypothesis: Experiments
Interpret Results, and revise the hypothesis if
necessary
State Conclusions in a form that can be
evaluated by others
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The Scientific MethodA police investigator comes to the scene of an accident
Observation?Hypothesis?
Experiments/tests?Interpret/revise hypothesis?
Conclusions?
Models describe only a part of reality
a replica or description designed to show the structure or workings of an object, system, or concept
Physicists decide which parts are important and which aren’t
Physicists use Models
Physicists use Models
E.g. Basketball
System: a set of items or interactions considered a distinct physical entity for the purpose of study.
In the basketball example you are studying the ball and its motion
Other factors such as color, size, spin, aren’t considered in the model
Physicists use ModelsReview:
A Model describes a part of reality
The system is what you are studying
Galileo’s Hypothesis
What was the Question?
What was his hypothesis?
How did he test his hypothesis?
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Controlled ExperimentExperiment involving manipulation of a single variable or factor
In order to test a hypothesis, you must change one variable at a time
Chapter 1 - The Science of PhysicsSection 1.2 - Measurements in Experiments
Measurements in experiments
Dimension: tells us what physical quantity we are dealing with.
Three basic dimensions:
Length
Mass
Time
Units: tells us how much of that physical quantity we are talking about
SI standardsIn 1960, an agreement was made on seven base units
We will deal with only three
Second (s)Time
Kilogram (kg)Mass
Meter (m)Length
UnitDimension
Prefixes
SI uses prefixes to accommodate extremes
The distance between stars is approximately
100 000 000 000 000 000 m
The distance between atoms in a solid is approximately 0.000 000 001 m
Mr. Samuel can’t even say those numbers
You shouldn’t be expected to say them either
These numbers are expressed in powers of 10.
The distance between stars is approximately 1 x 1017
The distance between atoms is 1 x 10-9m
Prefixes
Power Prefix Abbreviation Power Prefix Abbreviation
10-18 atto- a 101 deka- da
10-15 femto- f 103 kilo- k
10-12 pico- p 106 mega- M
10-9 nano- n 109 giga- G
10-6 micro- 1012 tera- T
10-3 milli- m 1015 peta- P
10-2 centi- c 1018 exa- E
10-1 deci- d
Converting MeasurementsUse conversion factor that will cancel with the units you are
given to provide the units you need.
The units to which you are converting should usually be in the numerator.
It helps to cross out the units that cancel
Lets PRACTICE
Practice 1AA human hair is approximately 50 m in diameter. Express
this diameter in meters.
A typical radio wave has a period of 1 s. Express this period in seconds
A hydrogen atom has a diameter of about 10nm.
Express this diameter in meters.
Express this diameter in millimeters.
Express this diameter in micrometers.
The distance between the sun and the Earth is about 1.5 x 1011 m. Express this distance with an SI prefix and in kilometers.
The average mass of an automobile in the United States is about 1.440 x 106 g. Express this mass in kilograms
Accuracy vs PrecisionAccuracy is the closeness of measurements to the correct or
accepted value of the quantity measured.
Precision is the closeness of a set of measurements of the same quantity made in the same way.
Accuracy vs Precision
Accuracy vs Precision
Accuracy vs Precision
Accuracy vs Precision
Accuracy vs Precision
Accuracy vs Precision
Accuracy suggests that the experiment has accounted for all factors that might affect the system being studied
Precision lets us know that the experiment was done carefully in a controlled environment
Accuracy vs Precision
PrecisionPrecision describes the limitations of the measuring instrument
Significant FiguresSignificant figures are used in science to indicate precision
Includes all the digits actually measured (18 cm), plus one estimated digit
In the pencil example we can estimate that it is 0.2 cm past the 18 cm mark.
Because 18.2 cm is an estimate, the true value is between 18.15 cm and 18.25 cm.
Significant FiguresWhen last digit is a zero, it is impossible to tell how many significant figures there are.
If we say 230 mm, is it between 225 mm and 235 mm or is it between 229.5 mm and 230.5 mm.
We solve this by recording it in scientific notation by expressing it as a power of 10.
If there are 2 significant figures we write it as 2.3 x 102 cm.
If there are 3 significant figures we write it as 2.30 x 102 cm.
Rules for zeros
Rules for calculating sig figs
Rules for roundingCalculators do not pay attention to
significant figures
Chapter 1 - The Science of PhysicsSection 1.3 - The Language of Physics
Mathematics and physicsMathematical tools are used to analyze and summarize observations in physics
Tables, graphs and equations can make data easier to understand
Mathematics and Physics
(change in position in meters) = 4.9 x (time of fall in seconds)2
Mathematics and Physics
Physicists use mathematics to describe measured or predicted relationships. between physical quantities in a situation
Physicists use letters to describe specific quantities.
(delta) means “difference or change in”
(sigma) means “sum” or “total”.yt
Mathematics and Physics
Dimensional Analysis
Dimensional analysis can weed out invalid equations.
Dimensions can be treated as algebraic quantities.
The two sides of any given equation must have the same dimensions.
Dimensional AnalysisHow long does it take a car driving at 88 km/h to drive a distance of 725 km?
length
time×length=
length
timeor
88km1.0h
×75km=6. ×10km
1.0h
length ÷lengthtime
=length×time
lengthor
75km×1.0h88km
=8. h
Order-of-magnitude estimations
It is often useful to estimate an answer before solving the problem.
This can be done with an order-of-magnitude calculation - determining the power of 10 closest to the actual numerical value.
In the car example:10
3 km
102 km/h
=10h
The answer should be closer to 10 than to 1 or 100
8.2 h is the correct answer and fits this range