This demonstration shows how the “pole in the barn paradox” plays out in a spacetime diagram. Choose the relative speed of the pole (the yellow line segment) and the barn (the blue line segment). Hit start to watch the pole move through the barn, or adjust the time slider to control its motion manually. Note that from the barn’s perspective, the pole  fits inside the barn at sufficiently high relative velocities. However, from the pole’s perspective, it does not fit inside the barn regardless of the relative velocity.