：。
Week 13: Study absolute motion and relative motion.
Literal
Ordinal-13th-week: absolute-motion [and-と] relative-motion [about-について] study.
A syllabus entry using 第 as an ordinal prefix with the counter 週. The bare dictionary form 学習する at the end is typical of schedule and syllabus writing — stating what will be covered rather than issuing a command. 絶対運動 and 相対運動 are Sino-Japanese physics terms: 絶対 (absolute) + 運動 (motion) and 相対 (relative) + 運動.