The purpose of this research was to determine the influence of implementation project based learning experiment to the students' concept mastery of rigid body equilibrium. This research used a Pre-Experimental Design with One-Shot Case Study form. The implementation of project based learning was obtained by students' performance that was conducted by during and after study process used observation sheet. The students' concept mastery was obtained by three-tier test instrument. Data analysis

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... simple linear regression test and t-test. The result of this research showed that the implementation of project based learning experiment influenced the students' concept mastery of rigid body equilibrium significantly. On the other hand, it was also found that project based learning effective in the positive development of the students' concept mastery.