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
과학자들은 중력계를 사용하여 지구의 중력을 측정합니다.gwahakjadeul-eun jungnyeokgye-reul sayonghayeo jiguu-ui junglyeog-eul cheugjeonghamnida.Scientists use a gravimeter to measure the gravity of the Earth.