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Unformatted text preview: PC1431 Physics IE
Introduction Learning Objectives To learn the basic laws of physics in mechanics and thermodynamics; to construct knowledge and mental linkages on one's own. To be able to apply these laws in various physical situations (problemsolving), and test the credibility of one's solutions. To think critically, ask the right questions, provide alternative solutions, and articulate ideas clearly (discussions, tutorials). To develop a deep enjoyment in learning physics, resulting in a desire to find out more on one's own. The Beauty of Physics Physics is the most fundamental physical science; concerned with basic principles of the Universe Foundation of other physical sciences (astronomy, chemistry, materials science, geology, etc.) Simplicity of fundamental physical theories; small number of fundamental concepts, laws, equations Areas of Physics Classical Mechanics motion of macroscopic objects at low speeds (v c) Relativity motion of objects at any speed Thermodynamics deals with heat, work, temperature, and the statistical behaviour of a large number of particles Electromagnetism theory of electricity, magnetism and electromagnetic fields Quantum mechanics theory dealing with behaviour of particles at atomic and macroscopic levels Domain of Classical Mechanics
Relativistic Quantum Mechanics c/10 Quantum Mechanics Classical Mechanics Cosmological Physics Relativity Relativistic Cosmology Nucleus (10 -14 m) Atom Man (10-10 m) (100 m) Galaxy (1020 m) Size Methodology of Physics Physics is based on experimental observation and quantitative measurements Objective is to use the minimum number of fundamental laws to predict results of future experiments Fundamental laws expressed in the language of mathematics which bridges theory and experiment When discrepancies arise between theory and experiments, new theories must be formulated (cf. Kuhn's paradigm of scientific revolution) A theory is often satisfactory and useful under limited conditions (e.g. classical mechanics), but a more general theory without limitations is still needed Development of Classical Mechanics Galileo (15641642) motion of objects under constant acceleration, Galilean transformation Kepler (15711630) planetary motion, Kepler's Laws Newton (16421727) developed classical mechanics as a systematic theory, Newton's Laws, calculus Other aspects of classical physics (thermodynamics, EM) not till late 19th century Development of Classical Mechanics Failure of classical mechanics to explain many physical phenomena in late 19th century led to: Theory of relativity (Einstein, 1905) motion of objects near speed of light (c), relativistic frames of reference Quantum mechanics (Planck, 1900, & others) physics at the atomic level Standards of Length, Mass & Time Laws of physics are expressed in basic quantities that require a precise definition In mechanics, the 3 basic quantities are length (L/m), mass (M/kg) and time (T/s); total of 7 SI base units All other physical quantities in mechanics can be expressed in terms of L, M and T. Length metre (m) defined as the distance travelled by light in vacuum during a time of 1/299 792 458 second (1983) Mass kilogram (kg) defined as the mass of a specific (very stable) PtIr alloy cylinder kept in France (1887) Time second (s) defined as 9 192 631 770 periods of radiation from Cs133 atoms (atomic clock, 1967) Dimensional Analysis Dimension denotes the physical nature of a quantity, e.g. length L Brackets [ ] used to denote dimensions, e.g. [v] = L/T (unit m/s) Dimensional analysis often used to: Dimensional analysis does not give any information on the magnitude of the constants of proportionality check a specific formula (both sides of equation must have same dimensions give hints as to the correct form the equations must take Order-of-Magnitude Calculations Useful to compute an approximate answer to a physical problem, even when insufficient information is available Results can be used to decide whether a more precise calculation is necessary Assumptions are usually needed "Make an estimate before every calculation, try a simple physical argument ...before every derivation, guess the answer to every puzzle. Courage: no one else needs to know what the guess is"
Taylor & Wheeler, Spacetime Physics (Freeman, SF, 1966) p.60. Measurement / Significant figures Uncertainty in measurement depends on the quality of the apparatus, skill of the experimenter and number of measurements performed e.g. take a metre rule length measurement of 16.30.1 cm calculated area = (16.3 cm)(4.5 cm) = 73 cm2 (not 73.35cm2); i.e. for multiplication & division, number of significant figures in answer = number of significant figures in least accurate input quantity For addition and subtraction, the number of decimal places = the smallest number of decimal places of input terms e.g. 123 + 5.35 = 128 (not 128.35) ...
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This note was uploaded on 04/17/2008 for the course PC 1431 taught by Professor Andrewwee during the Summer '04 term at National University of Singapore.
- Summer '04