Albert Einstein Theory of special relativity
Maybe the distance between the places where his basketball hits the floor of the airplane is about one meter or one yard. If some people are under the airplane they can mark the place directly under the airplane where the ball hits the floor. Those marks are a meter or maybe a yard apart. So everybody agrees that the bounces are about a meter or a yard apart. Later the plane takes off. People still watch it from on the ground. But this time bounce number 5 is over a place in Gibraltar and bounce number 6 is over a place in Spain. The distance between bounces is measured in kilometers or miles on the ground, but the people on the plane get the same answers they did while the plane was on the ground.