The material that the snails are moving on affects their speed. On a smooth material, (petri dish) the snails moved the fastest. On a rough material (sandpaper) the snails moved the slowest. On dirt, a compromise between smooth and rough, the snails moved at a medium pace. The material and possibly friction affect this.
football hemets have pads that are filled with air and thick foam so when they are hit the foam asorbs the hit and the air keeps the hard outer shell of the helmet from hiting the players head
There are correlation and causation between the force of the finger and the movement of the books
