Download Understanding Quantities in Science: Notation and Unit Conversion and more Lecture notes Physics in PDF only on Docsity! SCIENTIFIC NOTATION (i.e. how to handle small & big numbers without using up all the blackboard….) Sizes of objects exhibit such a great range that decimal point notation isn’t practical. For example…. in decimal pt notation.. Object size in cm size in miles Hydrogen atom 0.0000000106 0.000000000000065 Human hair 0.008 0.00000005 Boulder 1,000,000 6 Earth 1,274,200,000 7.865 Milky Way 160,000,000,000,000,000,000,000 987,654,320,587,654,000 Not practical!! SCIENTIFIC NOTATION 1 followed by “m” zeros = 10m ex. : 1,000,000 = 106 1 preceded by “m” zeros (including the one before the “dot”) = 10-m ex. : 0.000001 = 10-6 n followed by “m” zeros = n x 10m ex. : 3,000,000,000 = 3 x 109 n preceded by “m” zeros (including the one before the “dot”) = n x 10-m ex. : 0.000000003 = 3 x 10-9 PRACTICE: write the sizes of the objects of previous page in Sc. Not. “Dimension” of the waves at various energies
Radio waves
violet red »
Infrared and heat radiation
Centimeter waves
Decimeter waves
.
2
3
a
&
>
£
x
7 tadiation
Ultraviolet (UV)
Medium waves
Long waves
Short waves
m 10° 10° 1 10°
Wave length 1 nanometer 1 micrometer 1 millimeter 1 meter 1 kilometer
Synchrotron radiation
Different wavelengths “see” different parts of objects The hand seen through X-rays The hand seen in infrared The OY i GrsTenbeer DEENA [movie clip produced by NASA]
The Idea of a Black Hole John Michell (1783) , Pierre-Simon Laplace (1796): • Question: What happens if the escape speed from an object is greater than the speed of light? • Answer: If light consists of particles of matter, they would not be able to escape • The catch: early 19th cent - light is a wave (a disturbance), not a particle BH idea forgotten…. … until Einstein comes along “dark star” ? THE LAWS OF PHYSICS IN OUR “SLOW” WORLD Our everyday experience derives from a world where v<<c Let’s first introduce the concept of REFERENCE FRAME: It consists of an observer and a hypothetical bunch of instruments that can measure length, time, etc all in the same state of motion (i.e. not moving with respect to each other). Inertial reference frame: one not influenced by external forces. [drawings here and in next slides courtesy of D. Watson] Laws of Physics in a “slow” world built on the principles that: TIME AND SPACE ARE ABSOLUTE Given a meter stick and a clock in one reference frame: The stick appears of the same length in any other reference frame. The clock appears to tick at the same rate in any other reference frame. VELOCITIES ARE RELATIVE AND ADDITIVE How fast does the ball appear to roll?
V=10km/s ;
* That's just v0+ V = 15 km/s ———,
What if instead of a ball we have a light beam? How do we know? IT IS AN EXPERIMENTAL FACT. THE MICHELSON-MORLEY EXPERIMENT: 1887 Result of the experiment: NO DIFFERENCES IN TIMES ARE DETECTED First explanation put forward by Lorentz &Fitzgerald: There is a “force” that causes a contraction of lengths in the direction of the motion. The extent of this contraction is precisely such as to compensate for the longer travel time of the light pulses in the direction of motion. … until Einstein comes along… TRAVEL TIMES ARE THE SAME BECAUSE THE VELOCITY OF LIGHT IS THE SAME INDEPENDENT OF THE STATE OF MOTION [image from NASA collection] Finally, remember that, in classical mechanics, planets move in perfectly elliptical orbits, described by KEPLER’s laws.
