Special Theory Of Relativity
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Special Theory Of Relativity

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Special Theory Of Relativity Special Theory Of Relativity Presentation Transcript

  • SPECIAL THEORY OF RELATIVITY
    • Showed that Newton’s ideas of absolute space and absolute time were mistaken.
    • Implied that matter and energy were interconvertible.
    • Waves travel through a medium ( water, air)
    • Electromagnetic waves must travel through an undetectable medium in space called an ether.
    • Should be a difference if light travels in the direction of the Earth’s motion through the ether compared to right angles to it.
    • Michelson-Morley experiment showed no difference.
    • Hence no ether.
  • Motion
    • Motion is measured relative to a fixed point called a Frame of Reference
    • All bodies have inertia so resist any change to their motion
    • 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.
    • A Frame of Reference where Newton’s first law of motion is obeyed ,is called an
    • Inertial Frame
    • An Inertial Frame can have a constant velocity but cannot have an acceleration .
    • Any constant velocity of the spaceship is shared by everything inside it.
    • If you were inside, you could not detect this velocity.
    • 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.
    • No limit to the number of these restricted frames which can move relative to each other.
  • Key Ideas to Einstein’s Special Theory of Relativity
    • Newton’s idea of an inertial frame
    • Maxwell’s discovery that all types of electromagnetic radiation must travel at the same speed .
  • First Postulate of the special theory of Relativity
    • Einstein took Newton’s idea that the laws of motion apply to any inertial frame.
    • Extended it to include all the laws of physics.
  • Second Postulate of the special theory of relativity
    • The speed of all electromagnetic radiation is a fundamental law and applies to all inertial frames.
    • It is constant however it is measured from any inertial frame.
    • As the speed is constant ,an ether no longer makes any sense.
    • As Speed = Distance / Time
    • 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.
    • We need thought experiments to look at these ideas.
  • Time Dilation A B
    • If you are observer A and sent a pulse of light out at the same time as B.
    • B’s light would appear to travel further between reflections than A’s.
    • So B’s clock would appear to be running slower.
    • Likewise B would think A’s was running slower.
    • 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.
    • This is time dilation and affects any type of clock.
    • Life span of Muons can be increased by accelerating them to 99.7% of the speed of light.
    • The high proportion that reach the Earth’s surface when created in the upper atmosphere from cosmic rays, supports this.
  • Length contraction
    • The length of a train can be compared to the length of a tunnel.
    • Lamp x comes on as the train emerges
    • Lamp y comes on as the other end enters.
    • Observer A is by the track mid way in the tunnel.
    • Observer B is on the train at mid point.
    • Y X
    A B
    • Observer A sees both lights come on together
    • Observer B sees X come on before Y as he is travelling towards X and away from Y
    • This indicates that the train has left the tunnel before the end went in. So B thinks the train is longer than the tunnel.
    • √ 1 – v 2
    • c 2
  • General Theory of Relativity
    • Einstein wanted to link his theory to Newton’s Law of gravitation
    • Solved some of its problems.
    • E.g. the orbit of Mercury