पृथ्वी एक लगभग गोलाकार पिण्ड है। यदि इसके आंतरिक भाग में ऐसा पदार्थ हो जिसका घनत्व हर जगह समान न हो, तो पृथ्वी की सतह पर गुरुत्वीय त्वरण:

On Earth, g ≈ 9.8 m/s2. If an object is moved to a location where g = 0, its mass:

The force with which the Earth attracts an object is called:

Two stars of masses m and 2m at a distance d rotate about their common centre of mass in free space. Their period of revolution is: