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The four fundamental interactions

The four fundamental interactions

In order of increasing size are: gravity, the weak nuclear force, the electromagnetic force and the strong nuclear force.

Try Why Do Astronauts Float by Julian Hamm

The weak force

The word ‘force’ is a little misleading because it doesn’t involve pushes and pulls but the exchange of particles called bosons.

The weak force is still many trillion trillion times bigger than the gravitational force, which is only really noticeable when one object is about the mass of a planet.  But the weak nuclear force is of the order of a million times weaker than the ‘strong nuclear force’ that holds the nucleus together.

The fourth fundamental force is the electromagnetic force.


Objects only feel solid because of the electromagnetic repulsion between the electrons that make up all atoms.  So all of our sensations of touch and contact are because of the electromagnetic repulsion between us and other objects.

Electrons interact with each other by exchanging little packets of energy called photons.  This theory is called quantum electrodynamics (QED) and is one of the most successful theories in physics.

back to Lesson 10: Changes to the Nucleus