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I Observed speed of pitch different than catcher's view?

  1. Feb 24, 2017 #1
    I was reading Walter Isaacson's biography of Einstein recently, and I thought of moving walkways in airports.

    Let's say we have a pitcher and a catcher on the moving walkway 80 feet apart, and the pitcher throws the ball to the catcher, and the time that it takes to travel from the pitcher to the catcher is noted. Then, we should have the average speed for the throw or pitch.

    It seems to me that a stationary observer that is at a point, such that, the observer is across the hallway from the pitcher, and the observer, pitcher and catcher form a right triangle, will observe that the ball travels more than 80 feet. If the catcher then tells the observer how long the pitch took, then the observer will calculate a faster average speed.

    So, I am wondering (1) if my logic is correct, and (2) is this what is said to be a difference due to different frames of reference? Thank you for your help. Joe
  2. jcsd
  3. Feb 24, 2017 #2


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    Yes, the velocity of the ball to an external observer is the velocity of the ball within the system plus the velocity of the system. This is velocity addition in classical physics.

    Another example is two people sitting in a moving car where one hands an object to the other. In their reference frame the object is hardly moving, but to an external observer, the object is moving at the speed of the car.
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