Collisions never hurt just one thing. A crashing car never just damages itself. There is always a second object involved, which is also hurt or damaged. This is Newton’s 3rd law; the force one object feels, is also felt by another object.
It turns out that momentum behaves exactly the same.1 The momentum that one object loses, is gained by the impacted object.[1,2] The baseball bat is stopped/slowed down when hitting the baseball, and that ball is in turn gaining all that lost momentum and now moves fast the opposite way.
- ‘Conservation of momentum’ (web page), BC Open Textbooks, OpenStaxCollege, 2012, www.opentextbc.ca/physicstestbook2/chapter/conservation-of-momentum (accessed Feb. 27th, 2020)
- ‘College Physics for AP® Courses’ (book), Gregg Wolfe, Erika Gasper and others, OpenStax, 2015, www.physicsclassroom.com/class/momentum/Lesson-2/Momentum-Conservation-Principle (accessed Feb. 27th, 2020), ch. 8.3
- ‘Sears and Zemansky’s Univesity Physics with Modern Physics’ (book), Hugh D. Young & Roger A. Freedman, Pearson Education, 13th ed., 2012
- ‘Momentum Conservation Principle’ (web page), The Physic Classroom, www.physicsclassroom.com/class/momentum/Lesson-2/Momentum-Conservation-Principle (accessed Feb. 27th, 2020)