Weak nuclear force

The weak nuclear force (or just the weak force, or weak interaction) acts inside of individual nucleons, which means that it is even shorter ranged than the strong force. It is the force that allows protons to turn into neutrons and vice versa through beta decay. This keeps the right balance of protons and neutrons in a nucleus. The weak force is very important in the nuclear fusion that happens in the sun.[1] Nuclear fusion has also been created in laboratories, and that process requires the weak force to work too. See size of the universe for a list of visuals demonstrating how short ranged the weak force is.

As the name implies, the weak force is much weaker than the strong force, or the electromagnetic force, but it is quite a bit stronger than the gravitational force.

Modern physics has unified the electromagnetic and weak forces into the electroweak force. There is a continued effort to try to unify all of the forces in a grand unified theory.

Fully understanding the weak force takes many years of study, but some fun places to start include hyperphysics or the blog of Prof. Matt Strassler.

Below is the Scishow's series on fundamental forces part 2, the weak force:

For Further Reading

To learn about the other forces, please see the following pages:


  1. Sears and Zemanski's University Physics, 13th edition by Young and Freedman. Addison Wesley, 2010. Chapter 44, pg 1491.