Electromagetism

In Physics 101, we talked about the four fundamental forces:

1. Strong Nuclear Force
2. Electromagetism
3. Weak Nuclear Force
4. Gravity

Electromagnetism is what causes the normal force. The entire earth is pulling you towards the center and the electromagnetic force between your shoes and the ground is what prevents this.

Professor Goldberg is going to use the variable $\text{Q}$ to talk about charge. The unit of charge is a coulomb.

The most famous charged particle is an electron, its mass $m_e\text{,}=9.11\cdot 10^{31}\text{kg}$, its charge has a value of $-\text{e}$ and it’s charge is $1.6\cdot 10^{-19}\text{C}$. (Even though gravity goes down we’re using a positive number.) We use $+\text{e}$ to talk about the charge of a proton.

$\Delta Q=0$

Everything¹ can be broken down into protons (positive charge), neutrons and electrons (negative charge), with like charges repelling each other. This is actually the opposite of how gravity works, the gravity “equivalent” of charge is mass and masses attract.

It was Ben Franklin who came up with the idea that electrons are negative and protons, positive; this is totally arbitrary

In order to compute the electrostatic force, we use the formula $F=\frac{k{q}_1{q}_2}{r^2}$, with $k$ being the electrostatic constant. Well, $k$ is actually $\frac{1}{4\pi {\epsilon }_0}\approx 9\times 10^9\frac{\mathrm{N}{\mathrm{m}}^2}{{\mathrm{C}}^2}$.

$\vec{F}=q\vec{E}$

1/7/25

Footnotes

1. Me when I lie, see https://en.wikipedia.org/wiki/Quark ↩