Skip to ContentGo to accessibility pageKeyboard shortcuts menu
OpenStax Logo

Performance Task

PhysicsPerformance Task

Performance Task

7.2 Newton's Law of Universal Gravitation and Einstein's Theory of General Relativity


Design an experiment to test whether magnetic force is inversely proportional to the square of distance. Gravitational, magnetic, and electrical fields all act at a distance, but do they all follow the inverse square law? One difference in the forces related to these fields is that gravity is only attractive, but the other two can repel as well. In general, the inverse square law says that force F equals a constant C divided by the distance between objects, d, squared: F=C/ d 2 F=C/ d 2 .

Incorporate these materials into your design:

  • Two strong, permanent bar magnets
  • A spring scale that can measure small forces
  • A short ruler calibrated in millimeters

Use the magnets to study the relationship between attractive force and distance.

  1. What will be the independent variable?
  2. What will be the dependent variable?
  3. How will you measure each of these variables?
  4. If you plot the independent variable versus the dependent variable and the inverse square law is upheld, will the plot be a straight line? Explain.
  5. Which plot would be a straight line if the inverse square law were upheld?

Teacher Support

Magnets must be strong, such as neodymium magnets or cow magnets (ask a veterinarian). Suggest that they could either measure distance versus attractive force or repulsive force. Attractive force at various distances can be measured with the spring scale. Repulsive force could be measured by dropping the magnets into a transparent tube oriented so that they repel each other. The distance will be the distance between the magnets. Ask what the force will be. Ask how they could change the force and thereby change the distance.

Order a print copy

As an Amazon Associate we earn from qualifying purchases.


This book may not be used in the training of large language models or otherwise be ingested into large language models or generative AI offerings without OpenStax's permission.

Want to cite, share, or modify this book? This book uses the Creative Commons Attribution License and you must attribute Texas Education Agency (TEA). The original material is available at: . Changes were made to the original material, including updates to art, structure, and other content updates.

Attribution information
  • If you are redistributing all or part of this book in a print format, then you must include on every physical page the following attribution:
    Access for free at
  • If you are redistributing all or part of this book in a digital format, then you must include on every digital page view the following attribution:
    Access for free at
Citation information

© Jan 19, 2024 Texas Education Agency (TEA). The OpenStax name, OpenStax logo, OpenStax book covers, OpenStax CNX name, and OpenStax CNX logo are not subject to the Creative Commons license and may not be reproduced without the prior and express written consent of Rice University.