Transcript Physics 111
Physics 111 Honors Classical Mechanics Prof. Haimin Wang [email protected] http://solar.njit.edu/~haimin My Research: Solar Physics Instrumentation Magnetic Fields and Solar Activity Week 1 Chapter 1 Sections 1–6 – – – – – – Measurement International System of Units (SI System) Conversion of Units Length Time Mass Measurements Use laws of physics to describe many different physical systems – Small set of simple laws – Common language is mathematics Test laws by experiments – Select smallest set of standards and derive other standards – International Bureau of Weights and Measures (Paris), National Bureau of Standards, etc. – Système Internationale (SI), International System of Units, metric system, or mksA system SI Units Length meter m Mass kilogram kg Time second s Electric current ampere A Thermodynamic temperature kelvin K Luminous intensity candela cd Amount of substance mole mol Why should we care about SI units? Mars Climate Orbiter: http://mars.jpl.nasa.gov/msp98/orbiter Prefixes for SI Units 10x Prefix x=18 15 12 9 6 3 2 1 exa peta tera giga mega kilo hecto deca Symbol E P T G M k h da GeV MeV keV Prefixes for SI Units 10x Prefix x = 1 deci 2 centi 3 milli 6 micro 9 nano 12 pico 15 femto 18 atto Symbol d c m µ n p f a cm mm µm Nm Pm fm Example of Length Measurements Distance to 1st galaxies Distance to Nearest Star (Proxima Centauri) Distance to Pluto Radius of Earth Height of Mt. Everest Thickness of this page Radius of hydrogen atom Radius of a proton Length (m) 2x1026 4x1016 6x1012 6x106 9x103 1x10-4 5x10-11 1x10-15 Time 1 second is the time taken by 9,192,631,770 oscillations of the light emitted by cesium-133 atom Speed of light c=299,792,458 m/s Example of time Measurements Time (second) Age of Universe 5x1017 Length of a year 3x107 Length of a day 9x104 Lifetime of muon 2x10-6 Mass Standard 1: a platinum-iridium cylinder in Paris Standard 2: Carbon-12 has 12 atomic mass units (u). 1u=1.6605402x10-27 kg Example of mass Objects Sun Moon Ocean Liner Human Body Speck of dust Proton Electron Mass (kg) 2x1030 7x1022 7x107 6x10 7x10-10 2x10-27 9x10-31 Units Language is mathematics Equations Diagrams/visualization Quantities have dimensions Results have units Consistency Precision Measurements – Uncertainties • Absolute • Percent – Calculation • Result can not be better than data • Use scientific notation to show significant figures – Examples • 3.14 + 0.5 = 3.6 • 123,400,000 = 1.234 x 108 • 0.003 = 3 x 10-3 What is the radius r of the Earth? (h = 1.70 m and t = 11.1 s )