Question: One of Sarah's neighbors spilled dog food all over the stairs. The dog food pieces are on three stairways and all over the landings. Sarah gets mad and kicks a piece of dog food. The dog food flies across the wooden planks from one side of the staircase landing to the other which was 28 centi-meters long. The dog food reaches the neighbor's door mat. It just moves 10 centi-meters across the doormat and then stops. Why didn't the dog food move further across the doormat?? 
Option 1: The door mat is a spikier surface
Option 2: the staircase landing is a spikier surface
Answer: Option 1