Special Theory Of Relativity


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Special Theory Of Relativity

  2. 2. <ul><li>Showed that Newton’s ideas of absolute space and absolute time were mistaken. </li></ul><ul><li>Implied that matter and energy were interconvertible. </li></ul>
  3. 3. <ul><li>Waves travel through a medium ( water, air) </li></ul><ul><li>Electromagnetic waves must travel through an undetectable medium in space called an ether. </li></ul>
  4. 4. <ul><li>Should be a difference if light travels in the direction of the Earth’s motion through the ether compared to right angles to it. </li></ul><ul><li>Michelson-Morley experiment showed no difference. </li></ul><ul><li>Hence no ether. </li></ul>
  5. 5. Motion <ul><li>Motion is measured relative to a fixed point called a Frame of Reference </li></ul><ul><li>All bodies have inertia so resist any change to their motion </li></ul><ul><li>A spaceship in deep space ( minimal gravitational effects) would provide a frame of reference where a body would remain stationary or with a constant velocity unless a force was applied. </li></ul>
  6. 6. <ul><li>A Frame of Reference where Newton’s first law of motion is obeyed ,is called an </li></ul><ul><li>Inertial Frame </li></ul>
  7. 7. <ul><li>An Inertial Frame can have a constant velocity but cannot have an acceleration . </li></ul>
  8. 8. <ul><li>Any constant velocity of the spaceship is shared by everything inside it. </li></ul><ul><li>If you were inside, you could not detect this velocity. </li></ul>
  9. 9. <ul><li>If you are concerned by the acceleration of gravity, it is legitimate to think of an inertial frame on the Earth’s surface concerned only with horizontal forces or movements. </li></ul><ul><li>No limit to the number of these restricted frames which can move relative to each other. </li></ul>
  10. 10. Key Ideas to Einstein’s Special Theory of Relativity <ul><li>Newton’s idea of an inertial frame </li></ul><ul><li>Maxwell’s discovery that all types of electromagnetic radiation must travel at the same speed . </li></ul>
  11. 11. First Postulate of the special theory of Relativity <ul><li>Einstein took Newton’s idea that the laws of motion apply to any inertial frame. </li></ul><ul><li>Extended it to include all the laws of physics. </li></ul>
  12. 12. Second Postulate of the special theory of relativity <ul><li>The speed of all electromagnetic radiation is a fundamental law and applies to all inertial frames. </li></ul><ul><li>It is constant however it is measured from any inertial frame. </li></ul>
  13. 13. <ul><li>As the speed is constant ,an ether no longer makes any sense. </li></ul><ul><li>As Speed = Distance / Time </li></ul><ul><li>And there is constant relative velocity between any two inertial frames, then measurements by observers moving relative to each other must give different values of length and time. </li></ul>
  14. 14. <ul><li>We need thought experiments to look at these ideas. </li></ul>
  15. 15. Time Dilation A B
  16. 16. <ul><li>If you are observer A and sent a pulse of light out at the same time as B. </li></ul><ul><li>B’s light would appear to travel further between reflections than A’s. </li></ul><ul><li>So B’s clock would appear to be running slower. </li></ul><ul><li>Likewise B would think A’s was running slower. </li></ul>
  17. 17. <ul><li>The time interval between two events that occur in a particular inertial frame is longer when measured by someone moving relative to it than someone inside the frame. </li></ul><ul><li>This is time dilation and affects any type of clock. </li></ul>
  18. 18. <ul><li>Life span of Muons can be increased by accelerating them to 99.7% of the speed of light. </li></ul><ul><li>The high proportion that reach the Earth’s surface when created in the upper atmosphere from cosmic rays, supports this. </li></ul>
  19. 19. Length contraction <ul><li>The length of a train can be compared to the length of a tunnel. </li></ul><ul><li>Lamp x comes on as the train emerges </li></ul><ul><li>Lamp y comes on as the other end enters. </li></ul><ul><li>Observer A is by the track mid way in the tunnel. </li></ul><ul><li>Observer B is on the train at mid point. </li></ul>
  20. 20. <ul><li>Y X </li></ul>A B
  21. 21. <ul><li>Observer A sees both lights come on together </li></ul><ul><li>Observer B sees X come on before Y as he is travelling towards X and away from Y </li></ul><ul><li>This indicates that the train has left the tunnel before the end went in. So B thinks the train is longer than the tunnel. </li></ul>
  22. 22. <ul><li>√ 1 – v 2 </li></ul><ul><li>c 2 </li></ul>
  23. 23. General Theory of Relativity <ul><li>Einstein wanted to link his theory to Newton’s Law of gravitation </li></ul><ul><li>Solved some of its problems. </li></ul><ul><li>E.g. the orbit of Mercury </li></ul>