special relativity

• the interferometer reflected some light and let some pass through. these rays travelled to mirrors and reflected back to the original mirror to then be reflected onto a screen. an interference pattern occurred here
• the reflected rays path has a compensating plate so that each ray travels through the same amount of glass
• absolute motion is the idea that everything moves relative to a substance called the ether
• expectations of the Michelson Morley experiment

  • parallel speed affected but perpendicular not
  • rotating the equipment 90 degrees = shift in interference pattern
  • light moving parallel to earths motion takes longer than the other
• the Michelson Morley experiment showed that there was no shift in the interference pattern and so the time taken for light to travel is unaffected by rotation
• the Michelson Morley experiment showed that the ether does not exist and that the speed of light is invariant
• an inertial frame of reference is one where both objects are moving at a constant velocity relative to each other
• accelerating objects can not be in an inertial frame of reference
• Einstein's postulates

  • speed of light is invariant in free space
  • laws of physics are same for all inertial frames of reference
• time dilation is when time runs at different speeds depending on the motion of the observer
• a stationary observer is one that is stationary relative to the frame of reference of the event
• an external observer is one who's frame of reference is in motion
• muon decay provides evidence for special relativity as the expected count rate of their decay is very different to the actual count rate of their decay
• stationary observers have proper time / length
• external observers have measured time / length
• the proper time is always less than the measured time
• the proper length is always longer than the measured length
• length contraction is when high speed objects appear shorter to an external observer
• mass and energy are interchangeable
• faster objects have more energy and so more mass
• classical calculation of kinetic energy does not apply to relativistic speeds as there is a drastic change in mass
• relativistic speeds are those over 1/10th of the speed of light
• total energy is kinetic energy + rest energy
• relativistic energy can be found by multiplying relativistic mass by c^2
• bertozzis experiment involves firing electrons in pulses at an aluminium target. their speed is found by using the distance and time from release to target. when they collide, their kinetic energy is transferred to heat. this change in temperature is measured and used to find the energy with specific heat capacity equation. this is the kinetic energy. a graph is plotted of kinetic energy against speed
• bertozzis experiment showed the sharp increase of kinetic energy predicted by Einstein and relativity
• objects with mass can not travel at the speed of light as this suggests their mass tends to infinity and so their energy tends to infinity (impossible)
• to find kinetic energy of relativistic objects

  • E(kinetic) = E(total) - E(rest)
  • = mc^2 - moc^2
  • substitute mass dilation formula in for m