Physics of Technology PHYS 1800

1. Physics of TechnologyPHYS 1800 Lecture 38 Class Summary

2. PHYSICS OF TECHNOLOGYSpring 2009 Assignment Sheet *Homework Handout

3. Physics of TechnologyPHYS 1800 Lecture 39 So What Does It All Mean?

4. 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 Sense—A minimal set of simple, straightforward guides. • Units—Predictions on a quantitative level

5. Scientific Method: • Leads to new discoveries → how scientific progress is made! • Careful measurements, • Experiments • Empirical laws, • Generalization • Hypothesis,Theory

6. 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 people’s 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…)

7. 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.

8. What Do We Need To Measure? • What is the minimum about things we need to know? • Where things are—a length, L • When things are there—a time, t • How thing interact with gravity—a mass, M • How things interact with E&M—a charge, Q • How thing interact with weak nuclear force • How things interact with strong nuclear force • Random collections of objects—a temperature, T

9. Describing Motion Position—where you are in space (L-meter) Speed—how fast position is changing with time (LT-1 or m/s) Acceleration—how fast speed is changing with time (LT-2 or m/s2)

10. Dennison’s Laws of Motion • Stuff happens (or not). • The bigger they are the harder they fall. • You get what you give.

11. Newton’s Laws in Review • 1st Law—a special case of the 2nd Law for statics, with a=0 or Fnet=0 • 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).

12. Describing Motion and Interactions Position—where you are in space (L or meter) Velocity—how fast position is changing with time (LT-1 or m/s) Acceleration—how 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) Energy—the 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 object’s motion. KE=½ mv2 Potential Energy is the energy associated with an objects position. Gravitational potential energy PEgravity=mgh Spring potential energy PEapring= -kx Momentum— the potential of an object to induce motion in another object (MLT-1 or kg-m/s) Angular Momentum and Rotational Energy— the equivalent constants of motion for rotation (MT-1 or kg/s) and (MLT-2 or kg m/s2 or N)

13. Dennison’s Laws Thermal Poker(or How to Get a Hot Hand in Physics) • 0th Law: Full House beats Two Pairs • 1st Law: We’re playing the same game (but with a wild card) • 2nd Law: You can’t win in Vegas. • 3rd Law: In fact, you always loose. • 0th Law: Defines Temperature • 1st Law: Conservation of Energy (with heat) • 2nd Law: You can’t recover all heat losses • (or defining entropy) • 3rd Law: You can never get to absolute 0.

14. The Electrostatic and Gravitational Forces • The Newton’s Law of gravitation and Coulomb’s 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.

15. Dennison’s Laws of Fluids • When push comes to shove, fluids are just like other stuff. • Pascal’s Principle: Pressure extends uniformly in all directions in a fluid. • Boyle’s Law: Work on a fluid equals PΔV • Bernoulli’s Principle: Conservation of energy for fluids

16. Electric Circuits • Dennison’s Law of Circuit Analysis—Follow the electrons with your finger Dummy! (Conservation of charge and energy)

17. Waves • Waves is waves…they all • Transport energy • Interfere • Reflect • Refract • Diffract • Polarize • Principle of Superposition: When two or more waves combine, the resulting disturbance or displacement is equal to the sum of the individual disturbances.

18. 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!

19. 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 E&M, Weak NF • Quantum Mechanics • Schrodinger/Dirac Equation • Probabilistic approach

20. Limits of Current Modern Physics

21. PHYSICS OF TECHNOLOGY

22. Top Ten List of Things I Hope You Learned • Don’t waste your time remembering lots of equations or vocabulary (that’s what your book is for); go for the concepts! • There is not that much that we kneed to know (where stuff is and how stuff interacts)… • But the range of applications is enormous. • There are just four fundamental forces in nature. Newton’s Laws turn these into motion. • Stuff (mass, charge, energy, momentum, angular momentum) is conserved. • Your every day intuition is not always reliable (e.g., E&M, QM, relativity); you must rely on the careful, logical organization of observations to make valid predictions. • Our models reflect the patterns in nature (e.g., waves, oscillations and rotation are described by very similar math). • We know a lot of things about nature, but not everything (ask your grandkids to explain the TOE to you.). • Physics provides a (often useful) framework and methods to solve a wide variety of problems based on simple rules. • “With great power come awesome responsibility…”