Physics%20of%20Technology%20PHYS%201800

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Physics of TechnologyPHYS 1800

• Lecture 38
• Class Summary

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PHYSICS OF TECHNOLOGY Spring 2009 Assignment
Sheet
Homework Handout
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Physics of TechnologyPHYS 1800

• Lecture 39
• So What Does It All Mean?

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What is Physics?

• Study of the basic nature of matter and the
  interactions that govern its behavior.
• BORING!!!
• How Stuff Works.
• True, but vague.
• Common Sense Approach to How Things Work
• (with units!)
• Common SenseA minimal set of simple,
  straightforward guides.
• UnitsPredictions on a quantitative level

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Scientific Method

• Leads to new discoveries ? how scientific
  progress is made!
• Careful measurements,
• Experiments
• Empirical laws,
• Generalization

Hypothesis, Theory
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How are scientific explanations/laws developed?

• 1. Careful observations reveal an unknown natural
  phenomena(try to find answers - read books,
  search web)
• 2. Gather facts and measurements about phenomena,
  study other peoples ideas and try to develop an
  empirical law based on your results.
• 3. Invent a hypothesis to explain your
  observations and empirical laws.
• 4. Develop experiments to test your hypothesis.
  (Controlled experiments in laboratory
  preferably.)
• 5. Publish your results in scientific literature.
  (critical review)

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Why study everyday phenomena?

• The same physical principles that govern our
  everyday experiences also govern the entire
  universe
• A bicycle wheel, an atom, and a galaxy all
  operate according to laws for angular momentum.

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What Do We Need To Measure?

• What is the minimum about things we need to know?
• Where things area length, L
• When things are therea time, t
• How thing interact with gravitya mass, M
• How things interact with EMa charge, Q
• How thing interact with weak nuclear force
• How things interact with strong nuclear force
• Random collections of objectsa temperature, T

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Describing Motion

• Positionwhere you are in space (L-meter)
• Speedhow fast position is changing with time
  (LT-1 or m/s)
• Accelerationhow fast speed is changing with time
  (LT-2 or m/s2)

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Dennisons Laws of Motion

1. Stuff happens (or not).
2. The bigger they are the harder they fall.
3. You get what you give.

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Newtons Laws in Review

• 1st Law a special case of the 2nd Law for
  statics, with a0 or Fnet0
• An objects velocity remains unchanged, unless a
  force acts on the object.
• 2nd Law (and 1st Law)How motion of a object is
  effected by a force.
• The acceleration of an object is directly
  proportional to the magnitude of the imposed
  force and inversely proportional to the mass of
  the object. The acceleration is the same
  direction as that of the imposed force.
• 3rd Law Forces come from interactions with other
  objects.
• For every action (force), there is an equal but
  opposite reaction (force).

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Describing Motion and Interactions

• Positionwhere you are in space (L or meter)
• Velocityhow fast position is changing with time
  (LT-1 or m/s)
• Accelerationhow fast velocity is changing with
  time (LT-2 or m/s2)
• Force what is required to change to motion of a
  body (MLT-2 or kg-m/s2 or N)
• Inertia (mass) a measure of the force needed to
  change the motion of a body (M)
• Energythe potential for an object to do work.
  (ML2T-2 or kg m2/s2 or N-m or J)
• Work is equal to the force applied times the
  distance moved. W F d
• Kinetic Energy is the energy associated with an
  objects motion. KE½ mv2
• Potential Energy is the energy associated with an
  objects position.
• Gravitational potential energy PEgravitymgh
• Spring potential energy PEapring -kx
• Momentum the potential of an object to induce
  motion in another object (MLT-1 or kg-m/s)

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Dennisons Laws Thermal Poker(or How to Get a
Hot Hand in Physics)

• 0th Law Full House beats Two Pairs
• 1st Law Were playing the same game (but with a
  wild card)
• 2nd Law You cant win in Vegas.
• 3rd Law In fact, you always loose.

• 0th Law Defines Temperature
• 1st Law Conservation of Energy (with heat)
• 2nd Law You cant recover all heat losses
• (or defining entropy)
• 3rd Law You can never get to absolute 0.

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The Electrostatic and Gravitational Forces

• The Newtons Law of gravitation and Coulombs Law
  of electrostatic force has the same
  inverse-square dependence on distance as.
• If we double the distance between the charges,
  the force falls to one-fourth of the original.
• The gravitational force depends on the masses,
  and the electrostatic force depends on the
  charges.
• Gravity is always attractive there is no such
  thing as negative mass.
• Gravity is much weaker than the electrostatic
  force.
• Physicists are still trying to understand the
  reasons for the relative strengths of the
  fundamental forces.
• The search for a unified field theory that would
  explain the relationships between all of the
  fundamental forces is a major area of research in
  modern theoretical physics.

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Dennisons Laws of Fluids

• When push comes to shove, fluids are just like
  other stuff.
• Pascals Principle Pressure extends uniformly in
  all directions in a fluid.
• Boyles Law Work on a fluid equals P?V
• Bernoullis Principle Conservation of energy for
  fluids

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Electric Circuits

• Dennisons Law of Circuit AnalysisFollow the
  electrons with your finger Dummy!

(Conservation of charge and energy)
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Waves

• Principle of Superposition
• When two or more waves combine, the resulting
  disturbance or displacement is equal to the sum
  of the individual disturbances.

• Waves is wavesthey all
• Transport energy
• Interfere
• Reflect
• Refract
• Diffract
• Polarize

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What are the major subfields in Physics?

• Classical Physics (pre 20th century)
• Mechanics ? forces, motion
• Thermodynamics ? heat, temperature
• Electricity and magnetism ? charge, currents
• Optics ? light, lenses, telescopes
• Modern Physics (20th century)
• Atomic and nuclear ? radioactivity, atomic power
• Quantum mechanics ? basic structure matter
• Particle physics
• Condensed matter ? solids and liquids,
  computers, lasers
• Relativity, Cosmology ? universe, life!

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Current State of Physics cira 2009

• Conservation Laws
• Energy
• Linear Angular Momentum
• Charge, Spin
• Lepton and Baryon Number

• Statistical Mechanics
• Physics of many particles
• Fermions and Bosons
• Partitioning of Energy
• Thermodynamics
• Time and Entropy

• Weinburg-Salom Model
• QED
• Unites EM, Weak NF

• Quantum Mechanics
• Schrodinger/Dirac Equation
• Probabilistic approach

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Limits of Current Modern Physics
Dimension Range of Applicability Range of Application
Length 10-18 to 1026 m Quark size to the universe size
Mass 10-31 to 1040 kg Electrons to galactic clusters
Time 103 to 1022 sec-1 10-16 to 1017 sec Radio to Gamma rays Sub-femtosecond spectroscopy to age of universe
Velocity 10-8 to 108 m/s Sub-atomic particles to speed of light
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PHYSICS OF TECHNOLOGY
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Top Ten List of Things I Hope You Learned

1. Dont waste your time remembering lots of
   equations or vocabulary (thats what your book is
   for) go for the concepts!
2. There is not that much that we kneed to know
   (where stuff is and how stuff interacts)
3. But the range of applications is enormous.
4. There are just four fundamental forces in nature.
   Newtons Laws turn these into motion.
5. Stuff (mass, charge, energy, momentum, angular
   momentum) is conserved.
6. Your every day intuition is not always reliable
   (e.g., EM, QM, relativity) you must rely on the
   careful, logical organization of observations to
   make valid predictions.
7. Our models reflect the patterns in nature (e.g.,
   waves, oscillations and rotation are described by
   very similar math).
8. We know a lot of things about nature, but not
   everything (ask your grandkids to explain the TOE
   to you.).
9. Physics provides a (often useful) framework and
   methods to solve a wide variety of problems based
   on simple rules.
10. With great power come awesome responsibility