**ERIC Number:**EJ1055063

**Record Type:**Journal

**Publication Date:**2015-Feb

**Pages:**3

**Abstractor:**As Provided

**Reference Count:**11

**ISBN:**N/A

**ISSN:**ISSN-0031-921X

How Spherical Is a Cube (Gravitationally)?

Sanny, Jeff; Smith, David

Physics Teacher, v53 n2 p111-113 Feb 2015

An important concept that is presented in the discussion of Newton's law of universal gravitation is that the gravitational effect external to a spherically symmetric mass distribution is the same as if all of the mass of the distribution were concentrated at the center. By integrating over ring elements of a spherical shell, we show that the gravitational force on a point mass outside the shell is the same as that of a particle with the same mass as the shell at its center. This derivation works for objects with spherical symmetry while depending on the fact that the gravitational force between two point masses varies inversely as the square of their separation. If these conditions are not met, then the problem becomes more difficult. In this paper, we remove the condition of spherical symmetry and examine the gravitational force between two uniform cubes.

Descriptors: Science Instruction, Scientific Concepts, Scientific Principles, Physics, Motion, Geometric Concepts

American Association of Physics Teachers. One Physics Ellipse, College Park, MD 20740. Tel: 301-209-3300; Fax: 301-209-0845; e-mail: pubs@aapt.org; Web site: http://scitation.aip.org/tpt

**Publication Type:**Journal Articles; Reports - Evaluative

**Education Level:**N/A

**Audience:**N/A

**Language:**English

**Sponsor:**N/A

**Authoring Institution:**N/A