Harvard Natural Sciences Lecture Demonstrations | Bouncing Photon @NatSciDemos | Uploaded February 2011 | Updated October 2024, 1 hour ago.
A photon, modeled by a bouncing ping pong ball, is observed from a stationary frame bouncing up and down inside a moving cart. With respect to the stationary frame, the ball appears to move diagonally between bounces, whereas the ball appears to move straight up and down in the cart's frame of reference. In the stationary frame we observe that the ball travels a greater total distance than it does in the cart's frame.
If we now imagine the ping pong ball as a photon bouncing up and down between two mirrors, and if we postulate that the speed (the distance traveled in some amount of time) of a photon is the same in all (non-accelerating) reference frames, then time must move more slowly in the cart's frame of reference than it does in the stationary frame. This is one of the fundamental ideas behind Einstein's theory of special relativity.
The video is divided into two parts: in the first part we see Wolfgang pushing the cart at a (more or less) constant speed and the ball bouncing inside the cart; the second part is slowed down a bit more with a trace of the ball's path imposed on top of the footage (note: due to the distortion of the camera lens the ball appears to move at a slightly different angle after the last bounce).
Shot in 300 fps with a Casio Exilim EX-F1 camera--thanks to Rob for letting us use it!
A photon, modeled by a bouncing ping pong ball, is observed from a stationary frame bouncing up and down inside a moving cart. With respect to the stationary frame, the ball appears to move diagonally between bounces, whereas the ball appears to move straight up and down in the cart's frame of reference. In the stationary frame we observe that the ball travels a greater total distance than it does in the cart's frame.
If we now imagine the ping pong ball as a photon bouncing up and down between two mirrors, and if we postulate that the speed (the distance traveled in some amount of time) of a photon is the same in all (non-accelerating) reference frames, then time must move more slowly in the cart's frame of reference than it does in the stationary frame. This is one of the fundamental ideas behind Einstein's theory of special relativity.
The video is divided into two parts: in the first part we see Wolfgang pushing the cart at a (more or less) constant speed and the ball bouncing inside the cart; the second part is slowed down a bit more with a trace of the ball's path imposed on top of the footage (note: due to the distortion of the camera lens the ball appears to move at a slightly different angle after the last bounce).
Shot in 300 fps with a Casio Exilim EX-F1 camera--thanks to Rob for letting us use it!
