The Gravitational Potential Energy of a system of 2 masses is always negative. Why is that? According to Newton’s universal law of gravitation, when two masses are infinitely distant, the gravitational force / interaction is zero, thus the potential energy is zero. To bring them closer, the work on the system must be negative. The work being a transfer of energy, the potential energy can thus only be negative.

In a second part of the video, I also prove that by deriving the formula for gravitational potential energy: a minus sign appears while all the variables involved are positive in nature.

Finally, the last part of the video widens our understanding with a generalisation: The sign of potential energy is negative when the interaction is attractive, and positive when it is repulsive.

0:00 – Why is gravitational potential energy always negative (Introduction)
0:37 – Reminder that work is a transfer of energy (notion needed for the proofs that follow)
1:33 – Explains why gravitational Potential energy is always negative
4:02 – Deriving the formula for gravitational potential energy (based on Newton’s Universal Law of Gravitation)
7:10 – Sign of potential energy (general rule)
10:31 – Conclusion and card links to useful videos:
What is Energy    • What is Energy?  
What is Work    • What is Work? (High School Physics)  

For a deeper dive into the basics of Gravity, here is a fantastic course on the subject:
https://www.udemy.com/course/gravity...


This video is produced and presented by Edouard Reny, Ph.D. in solid state chemistry and private tutor in Physical Sciences.

For access to great resources that will help you with your studies of high school Physics, visit and subscribe to the "Physics Made Easy" website:
https://www.physicsmadeeasy.com/

Edouard provides oneonone private tuition in Physics (face to face or by Skype). If you wish to contact him, visit his website: https://www.physicstutor.nl/


Footage credit (Space background at end of video):
Traverse galaxy, F. Summers, G. Bacon (STScI). Simulation: C Hummels, P. Hopkins (CalTech) and A. Wetzel (UC Davis)

Credit for Thumbnail image: AllenMcC. / CC BYSA