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Physics 350 General Physics I: Mechanics, Heat and Sound

Physics 350 General Physics I: Mechanics, Heat and Sound. Course Structure. Full class meets 2 times per week in FL2-208 MW 5:30 –6:50 PM Lectures PowerPoint presentations Lecture materials will be made available on the web Work out example problems and questions Demonstrations

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Physics 350 General Physics I: Mechanics, Heat and Sound

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  1. Physics 350General Physics I:Mechanics, Heat and Sound

  2. Course Structure • Full class meets 2 times per week in FL2-208 • MW 5:30–6:50 PM • Lectures • PowerPoint presentations • Lecture materials will be made available on the web • Work out example problems and questions • Demonstrations • Laboratory section meets twice a week following lecture • MW 7:00–8:20 PM: FL2-208 • Opportunity for discussions on course material, exam prep, etc.

  3. Resources • Your Fellow Students! • Encouraged to work together on homework, exercises (but not on exams!) • Tutoring: Tutoring center located in Aspen Hall room FL1-108 or the Reading, Writing, and Math Center at Cypress Hall FL2-239 • Instructor! • Office in FL2-208, office hours F 4:00 PM – 5:00 PM, or by appointment mondays@flc.losrios.edu • Web: flc.losrios.edu/~mondays • Lecture presentations, updates, HW assignments/solutions • Text • Physics, Sixth Edition, Giancoli

  4. Course Objectives • Explore the approach that physics brings to bear on the world around us • Scientific Method • Quantitative Models • Reductionism

  5. Course Objectives, continued • Appreciate the influence physics has on us all • Begin to see physics in the world around you • Develop your natural intuition, stimulate curiosity • Think into the unknown (ooh that’s scary!) • Understand basic laws of physics • Newton’s laws of motion, gravitation • Concepts of mass, force, acceleration, energy, momentum, power, etc. • Fluid mechanics, mechanical waves (including sound), and thermodynamics.

  6. What’s with these questions/observations? • Science is as much about questions as answers. • You may have questions about: • Something you’ve always wondered about • Something you recently noticed • Something that class prompted you to think about • Goal is to increase your awareness, observational skills, analytical skills • We’re immersed in physics: easy to ignore, but also easy to see! • You’ll begin to think more deeply before shoving problem aside • Allow your natural curiosity to come alive

  7. Expectations • Attend lectures and laboratory section • Participate! • If it doesn’t make sense, ask! Everyone learns that way. • Don’t be bashful about answering questions posed. • Do the work: • It’s the only way this stuff will really sink in • exams become easier • Explore, think, ask, speculate, admire, enjoy! • Physics can be fun

  8. Does it Pay to Come to Lecture? • No one who came more than 80% of time did very poorly • Few who came infrequently got more than a low B

  9. Any Questions on Course Structure?

  10. What is “Physics” • An attempt to rationalize the observed Universe in terms of irreducible basic constituents or simplest form, interacting via basic forces. • Reductionism! • An evolving set of (sometimes contradictory!) organizing principles, theories, that are subjected to experimental tests. • This has been going on for a long time.... with considerable success

  11. Kepler’s laws of planetary motion Falling apples Universal Gravitation “Unification” of forces Reductionism • Attempt to find unifying principles and properties e.g., gravitation:

  12. Should we even pay attention, then? • Physics is always on the move • theories that long stood up to experiment are shot down • But usually old theory is good enough to describe all experiments predating the new trouble-making experiment • otherwise it would never have been adopted as a theory • Ever higher precision pushes incomplete theories to their breaking points • Result is enhanced understanding • deeper appreciation/insight

  13. Mathematics: the natural language of Physics Engineering Biology Geology Chemistry Astronomy Physics Physical Reality Our Universe Abstraction Mathematics Logic, Numbers, Operators

  14. To Start: • First Up – Review • Next Lectures – Kinematics • Assignments: • Check out course web page: • flc.losrios.edu/~mondays • Reading: • Giancoli, Chapter 1

  15. Physics 350Chapter 1: Review

  16. Review: • Units • Any measurement or quantitative statement requires a standard to compare with to determine its quantity • If I go a speed of 30, how fast am I going? • Mi/hr. km/hr, ft/sec • Units help us to quantify against a known standard

  17. Measurements • Basis of testing theories in science • Need to have consistent systems of units for the measurements • Uncertainties are inherent • Need rules for dealing with the uncertainties

  18. Systems of Measurement • Standardized systems • agreed upon by some authority, usually a governmental body • SI -- Systéme International • agreed to in 1960 by an international committee • main system used in this course • also called mks for the first letters in the units of the fundamental quantities

  19. Systems of Measurements • cgs -- Gaussian system • named for the first letters of the units it uses for fundamental quantities • US Customary • everyday units (ft, etc.) • often uses weight, in pounds, instead of mass as a fundamental quantity

  20. Basic units • Three basic quantitative measurements • Length • Mass • Time • All units can be reduced to these three units!

  21. Length • Units • SI -- meter, m • cgs -- centimeter, cm • US Customary -- foot, ft • Defined in terms of a meter -- the distance traveled by light in a vacuum during a given time (1/299 792 458 s)

  22. Mass • Units • SI -- kilogram, kg • cgs -- gram, g • USC -- slug, slug • Defined in terms of kilogram, based on a specific Pt-Ir cylinder kept at the International Bureau of Standards

  23. Standard Kilogram

  24. Time • Units • seconds, s in all three systems • Defined in terms of the oscillation of radiation from a cesium atom (9 192 631 700 times frequency of light emitted)

  25. Time Measurements

  26. US “Official” Atomic Clock

  27. 2. Dimensional Analysis • Dimension denotes the physical nature of a quantity • Technique to check the correctness of an equation • Dimensions (length, mass, time, combinations) can be treated as algebraic quantities • add, subtract, multiply, divide • quantities added/subtracted only if have same units • Both sides of equation must have the same dimensions

  28. Dimensional Analysis • Dimensions for commonly used quantities Length L m (SI) Area L2 m2 (SI) Volume L3 m3 (SI) Velocity (speed) L/T m/s (SI) Acceleration L/T2 m/s2 (SI) • Example of dimensional analysis distance = velocity · time L = (L/T) · T

  29. 3. Conversions • When units are not consistent, you may need to convert to appropriate ones • Units can be treated like algebraic quantities that can cancel each other out 1 mile = 1609 m = 1.609 km 1 ft = 0.3048 m = 30.48 cm 1m = 39.37 in = 3.281 ft 1 in = 0.0254 m = 2.54 cm

  30. Example 1. Scotch tape: Example 2. Trip to Canada: Legal freeway speed limit in Canada is 100 km/h. What is it in miles/h?

  31. Prefixes • Prefixes correspond to powers of 10 • Each prefix has a specific name/abbreviation Power Prefix Abbrev. 1015 peta P 109 giga G 106 mega M 103 kilo k 10-2 centi P 10-3 milli m 10-6 micro m 10-9 nano n Distance from Earth to nearest star 40 Pm Mean radius of Earth 6 Mm Length of a housefly 5 mm Size of living cells 10 mm Size of an atom 0.1 nm

  32. Example: An aspirin tablet contains 325 mg of acetylsalicylic acid. Express this mass in grams. Solution: Given: m = 325 mg Find: m (grams)=? Recall that prefix “milli” implies 10-3, so

  33. 4. Uncertainty in Measurements • There is uncertainty in every measurement, this uncertainty carries over through the calculations • need a technique to account for this uncertainty • We will use rules for significant figures to approximate the uncertainty in results of calculations

  34. Significant Figures • A significant figure is one that is reliably known • All non-zero digits are significant • Zeros are significant when • between other non-zero digits • after the decimal point and another significant figure • can be clarified by using scientific notation 3 significant figures 5 significant figures 6 significant figures

  35. Operations with Significant Figures • Accuracy -- number of significant figures • When multiplying or dividing, round the result to the same accuracy as the least accurate measurement • When adding or subtracting, round the result to the smallest number of decimal places of any term in the sum meter stick: Example: 2 significant figures rectangular plate: 4.5 cm by 7.3 cm area: 32.85 cm2 33 cm2 Example: Example: 135 m + 6.213 m = 141 m

  36. Order of Magnitude • Approximation based on a number of assumptions • may need to modify assumptions if more precise results are needed • Order of magnitude is the power of 10 that applies Question: McDonald’s sells about 250 million packages of fries every year. Placed end-to-end, how far would the fries reach? Solution:There are approximately 30 fries/package, thus: (30 fries/package)(250 . 106 packages)(3 in./fry) ~ 2 . 1010 in ~ 5 . 108 m, which is greater then Earth-Moon distance (4 . 108 m)! Example: John has 3 apples, Jane has 5 apples. Their numbers of apples are “of the same order of magnitude”

  37. Math Review: Trigonometry • Pythagorean Theorem

  38. Example: how high is the building? Known: angle and one side Find: another side Key: tangent is defined via two sides! a

  39. Math Review: Coordinate Systems • Used to describe the position of a point in space • Coordinate system (frame) consists of • a fixed reference point called the origin • specific axes with scales and labels • instructions on how to label a point relative to the origin and the axes

  40. Types of Coordinate Systems • Cartesian • Plane polar • Spherical • Cylindrical

  41. Cartesian coordinate system • also called rectangular coordinate system • x- and y- axes • points are labeled (x,y)

  42. Plane polar coordinate system • origin and reference line are noted • point is distance r from the origin in the direction of angle , ccw from reference line • points are labeled (r,)

  43. Relationship Between Polar and Rectangular Coordinates • Looking at the figure, we can see that leading to the relationship • This is how you would change polar coordinates to rectangular coordinates.

  44. Relationship Between Polar and Rectangular Coordinates • Looking at the figure, we can also see that • This is how you would change rectangular coordinates to polar coordinates.

  45. Example 1 • Find the rectangular coordinates of the point P whose polar coordinates are (6, 2p/3).

  46. Example 1 • Find the rectangular coordinates of the point P whose polar coordinates are (6, 2p/3). • Since r = 6 and q = 2p/3, we have

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