Transcript Document
Last Lecture Ideal Gas Law Today What was so great abut 1905? Important Concepts If you were very small or moved very fast, the world would be a very strange place. 8.01L Fall 2005 12/13/2005 Important Reminders No more 8.01L assignments this semester. We resume on Monday morning, January 9. Switching of recitations will be permitted if you have a conflict with another IAP activity. 8.01L Fall 2005 12/13/2005 1905 - Einstein’s “Miracle Year” Einstein submitted 5 papers, 4 were very significant, 3 were revolutionary Motions of molecules in solution indicates their size Brownian motion shows that atoms are real Light is composed or particles (photons) Special relativity E=mc2 8.01L Fall 2005 12/13/2005 Brownian Motion Random motion of small particles in fluid Brownian Motion Applet Einstein used kinetic theory to show that this motion could be explained by the statistical process of many collisions of molecules Detailed predictions of properties of the motion verified three years later. So, atoms are real (still controversial at the time) Still an active area of research! 8.01L Fall 2005 12/13/2005 Photons Light was known to be an electromagnetic wave The photoelectric effect, in which light kicks electrons out of metals, had strange properties Einstein showed that these experimental effects could be explained if light was composed of little packets, each with a fixed energy and momentum Later development of quantum mechanics (which Einstein never liked) showed that particles can also act like waves 8.01L Fall 2005 12/13/2005 Special Relativity Simple assumptions: Light moves at the same speed for all observers Speed, usually denoted with the symbol “c”, has a value very close to 3×108 m/s Predicted by Maxwell (this is taught in 8.02) All observers in inertial frames see the same physics One of the bedrock assumptions of all of mechanics 8.01L Fall 2005 12/13/2005 Special Relativity Profound consequences: Space and time are closely intertwined Different observers cannot agree on whether two events are simultaneous or occur at the same place Moving objects get smaller (Lorentz contraction) Moving clocks run slower (time dilation) Moving objects have more inertia 1 2 v 1 c ~15% for v~50% of c, ~factor of 7 for v~99% of c The size of most effects varies like 8.01L Fall 2005 12/13/2005 E=mc2 Einstein showed that this connection was a direct consequence of special relativity As mentioned before, the inertial mass of an object also rises as its speed approaches the speed of light A small mass packs a huge energy Lots of energy is also equivalent to mass This can make gravity complicated; mass creates gravitational potential energy which is itself a form of mass which creates more energy ⇒ General Relativity 8.01L Fall 2005 12/13/2005 See you next year! Happy Holidays! Good luck on your finals! 8.01L Fall 2005 12/13/2005