# Explain why the gravitational potential at any point outside an isolated, uniform spherical mass is negative, and describe how this potential changes as a small test mass is moved from the surface of the sphere to a very large distance away.

> IB DP Physics Higher Level (2023 syllabus) — D.1 Gravitational fields · Explain · 4 marks

## Mark scheme (4 marks)

1. Gravitational potential is defined as zero at infinity (at an infinite distance from the mass).
2. Work must be done by an external agent (energy must be supplied) to move the test mass from any finite distance to infinity, so the potential at any finite distance must be less than zero / is negative.
3. As the test mass is moved away from the surface, the gravitational potential increases (becomes less negative / increases towards zero).
4. The potential approaches zero asymptotically as the distance becomes very large / tends to infinity, and the rate of increase decreases with distance (potential varies as −1/r so the gradient decreases).

## Key terms

- [gravitational potential](https://www.gradenine.co.uk/glossary/gravitational-potential)
- [test mass](https://www.gradenine.co.uk/glossary/test-mass)

## Related

- [Revision notes for IB DP Physics Higher Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-the-gravitational-potential-at-c11691ea) · Published by Druglandscape Ltd.