The Science of Physics

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Chapter 1

• The Science of Physics

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1-1 What is Physics?

• We are surrounded by the principles of physics in
  our everyday lives.
• Any problem or question that deals with
  temperature, size, motion, position, shape or
  color involves physics.

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The Areas of Physics
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• Classical Mechanics
• motion of macroscopic objects at low speeds (v
  ltlt c)

Examine motion its causes. Ex falling objects,
weight, friction, etc.
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• Thermodynamics
• deals with heat, work, temperature, and the
  statistical behaviour of a large number of
  particles

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• Vibrations Waves
• Deals with specific types of repetitive motion.
• Ex springs, pendulums, sound

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• Optics
• Deals with light and its properties.
• Ex mirrors, lenses, color

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• Electromagnetism
• theory of electricity, magnetism and
  electromagnetic fields
• Ex electric charge, circuits, permanent magnets

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• Relativity
• motion of objects at any speed, including very
  high speeds
• Ex particle collisions, nuclear energy

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• Quantum mechanics
• theory dealing with behaviour of particles at
  atomic levels

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The Science of Physics
Thermodynamics Heat and temperature Efficient
engines, coolants
Electromagnetism Battery, starter, headlights
Optics Headlights, rear-view mirrors
Vibrations and Mechanical waves shocks, radio
speakers sound insulation
Mechanics Spinning motion of the wheels, tires
that provide enough friction for traction all
motions
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Scientific Method

• Make observations collect data that lead to a
  question.
• Formulate and objectively test hypotheses by
  experiment.
• Interpret results, and revise hypothesis if
  necessary.
• State conclusions in a form that can be evaluated
  by others.

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Models in physics

• A model is a replica or description designed to
  show the structure or workings of an object,
  system or concept.
• Simplify
• Help build hypotheses
• Guide experimental design
• Make testable predictions

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1-2 Measurement
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Physical Quantity vs. Units

• Physical quantity- any characteristics of objects
  that can be measured.Ex length, mass,
  temperature
• Units of measure- basic standards of
  measurementEx length can be measured in miles
  or meters

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SI Standards
UNIT Original standard Current standard
Meter (length) 1/10,000,000 distance from equator to North Pole Distance traveled by light in a vacuum in 3.3 x 10-9 s
Kilogram (mass) Mass of 0.0001 cubic meters of water Mass of a specific platinum-iridium alloy cylinder
Second (time) (1/60)(1/60)(1/24) 0.00001574 average solar days 9,192,631,700 times the period of a radio wave from cesium-133
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• Other units are DERIVED units, that is, they are
  calculated from measurements in the base units.
• Examples are velocity (m/s), acceleration (m/s2),
  or density (g/cm3).

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Prefixes

• Symbolize powers of 10
• Used to accommodate very large/small quantities
• Commonly used prefixes on table 1-3, pg. 12

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Conversions

• Conversion factor- ratio used to convert from one
  unit or prefix to another
• Used in the factor-label method to express
  answers in the desired units.
• Example1 mile 1.61 km

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• ExampleConvert 10.0 miles into kilometers
• Conversion factor 1 mile 1.61 kmSet up the
  conversion so that miles cancel when multiplied
  km 10.0 mi x 1.61 km 16.1 1
  mile

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Sample Problem

• Oh man, a bleary-eyed student once noted, That
  lecture on classroom policies must have gone on
  for a microcentury. How many minutes are there
  in a microcentury?

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Solution

• Micro 10-6

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Accuracy Precision

• Accuracy- how close a measurement comes to
  accepted value
• Precision- degree of exactness, small variation
  between repeated measurements

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Measurement / Significant figures

• Uncertainty in measurement depends on the quality
  of the apparatus, skill of the experimenter and
  number of measurements performed
• Sig figs keep track of imprecision
• Sig figs include all measured digits plus one
  estimated digit

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• Sig Figs

10.3 read as much as you can and estimate one
digit
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12
10
10.30 read as much as you can and estimate one
digit
10
11
12
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The rules for significant digits

• 1. All whole number digits are significant.
• Ex. 1, 2, 3, 4, 5, 6, 7, 8, 9
• 245,955 6 significant digits
• 14,328 ________________
• 96 ________________

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The rules for significant digits

• 2. Rules for Zeros
• a. Zeros between other nonzero digits are
  significant.
• Example
• 404 3 significant digits
• 40530004 _____________
• 606060606 _____________

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The rules for significant digits

• b. Zeros in front of nonzero digits are not
  significant
• Example
• 00222 3 significant digits
• 0.00556 ______________
• 00000000001 ____________

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The rules for significant digits

• c. Zeros that are at the end of a number and also
  to the right of the decimal are significant.
• Example
• 120.00 5 significant digits
• 4052.00000 ______________
• 30302.0 ______________

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The rules for significant digits

• d. Zeros at the end of a number without a decimal
  are not significant.
• Example
• 300 1 significant digit
• 46000 ______________
• 460.00 ______________

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The rules for significant digits in calculations

• 1. Addition or subtraction - The final answer
  should have the same number of digits to the
  right of the decimal as the measurement with the
  smallest number of digits to the right of the
  decimal.

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• Example
• 4.02 6.11 4.9 15.0 (15.03)
• 6.111 12.31 1.2 _________
• 10.256 2.44 1.6 ________

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The rules for significant digits in calculations

• 2. Multiplication or division the final answer
  has the same number of significant figures as the
  measurement having the smallest number of
  significant figures.

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• Example
• 4.0 x 2.11 x 3.456 29
• (actual answer is 29.16864)
• 4.01 x 4.1 / 4.012 _______
• 16.211 / 4.211 / 2 _______

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Scientific Notation

• Scientific Notation- in the form of A x 10 n
• 1lt Alt 10 and n power of 10
• A contains only sig figs of original
  number/measurement

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1-3 Language of Physics

• Tables, Graphs, Equations

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• Tables, graphs equations make data easier to
  understand
• Equations used to describe relationship between
  physical quantities
• Appendix B pg 952-960 lists variables, symbols
  constants used

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Dimensional Analysis

• Dimensional analysis used to
• - check a specific formula
• - give hints as to the correct form the
  equations must take
• Dimensional analysis does not give any
  information on the magnitude of the constants of
  proportionality

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Orders-of-Magnitude

• Refers to the nearest power of 10
• Useful to compute an approximate answer
• Results can be used to decide whether a more
  precise calculation is necessary
• Assumptions are usually needed