How does a catalyst work?

A catalyst works by providing a different pathway for the reaction, one that has a lower activation energy than the uncatalyzed pathway. This lower activation energy means that a larger fraction of collisions are successful at a given temperature, leading to an increased reaction rate.

Explanation:

Khan Academy is a great homework site:

https://www.khanacademy.org/science/ap-chemistry-beta/x2eef969c74e0d802:kinetics/x2eef969c74e0d802:catalysis/v/catalysts

you can also use this video:

https://youtu.be/if5JGssffm8

stress fractures occur largely in the feet and legs and are common in sports that require repetitive impact, primarily running/jumping sports such as gymnastics or track and field.