Hello, Im a ninth grade student in high school and I have a science fair project experiment idea. There will be a homemade marble shooter made with a rubber band. the rubber band will be pulled about half of a foot back and will propel a marble through a tube. the marble will hit a book and the marble's momentum will cause it to roll back. The distance of away from the book to the marble shooter will be a foot. The levels of independent variable will be marbles with completely different weights. This experiment will be used to find out momentum. How do I calculate do momentum for this experiment. Remember im a ninth grader so please dont get too technical.