Chapter 4 – Forces

Electromagnetism

There are four forces in nature:

• Gravity: not covered by quantum mechanics
• Electromagnetism: Responsible for almost all everyday phenomena, including light, electricity, magnetism, and the chemical bonds that hold molecules together.
• Strong nuclear force: Short range – binds quarks together to form protons and neutrons, and binds those protons and neutrons tightly together inside atomic nuclei
• Weak nuclear force: Extremely short range – responsible for particle decay and radiation

The Standard Model covers all these forces except gravity.

Electromagnetic force

The electromagnetic force is mediated by the photon

The electromagnetic force causes like charges to repel and opposite charges attract. How does a photon do that?

Think of the electromagnetic field as a flexible sheet and the charged particles create patterns in the sheet

When photons go between the particles, they create disturbances that move between the particles

Depending on whether the charges have the same or opposite sign, the disturbance nudges the particles apart or together