Last Lecture

1

• 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.

2
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.

3
1905 - Einsteins 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
• Emc2

4
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!

5
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

6
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 3108 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

7
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
• The size of most effects varies like
• 15 for v50 of c, factor of 7 for v99 of c

8
Emc2

• 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

9
See you next year!Happy Holidays!Good luck on
your finals!