Black Friday: lifetime access is on a special offer in the app, until November 30. Black Friday: special offer on lifetime access, until November 30. Download
물체의 중심계에서 모든 힘은 균형을 이룹니다.Mulche-ui jungsimgyeeseo modeun him-eun gyunhyeong-eul il-eumnida.In the center of mass system of the object, all forces are balanced.