A pebble fell freely from a certain height above the ground, and a photographer just caught its trajectory of falling ab. camera operator ...

Let the distance between pebbles and starting point A be S 1(m), the time when pebbles arrive here be t 1(s), the distance between pebbles and starting point A be S2(m) and the time when pebbles arrive here be t2(s), then: S2-s1= (65438+)