Particles have a property named charge. It can be positive or negative.

Like charges repel, opposite charges attract.

Unit of charge is a Coulomb.

Protons and electrons have a charge. Neutrons have no charge.

e, the elementary charge, is the charge of a proton. The charge of an electron is -e.

$$ C = {one Coulomb} = 6.24 * 10^{18}e $$

inverse is

$$ e = 1.6 * 10^{-19} C $$

$$ F_e = \frac{k_eq_1q_2}{d^2} $$

Where Fe is the static electric force in Newtons (N).

K is a constant ke, approx 9* 10^9. This is Coulomb's constant, electric force constant or electrostatic constant.

q1 is the charge of the first particle (in Coulombs).

q2 is the charge of the second particle.

d is the distance in metres.

If the number is negative, it means the the particles will be attracted to each other.

intro to charge at Khan Academy.

Electric fields

If you have 1 charged particle, it creates an electric field.

The field can be described in Newtons per Coulomb (N/C).

Assume the charge of the particle is q, then at distance d, the electric field can be given as:

$$ E = \frac{k_eq}{d^2} $$

If you put another particle, with charge q2, into the electric field, then the static electric force will be

$$ F = Eq_2 $$

electrostatics at Khan Academy.


Energy and Work

Kinetic energy is stored in a moving object of mass m moving at velocity v.

Gravitational potential energy is stored by lifting an object higher.

Newton metres

Force * distance

Units would be N*m

For a moving block of mass m:

$$ KE = \frac {m.v^2}{2} $$


J is the symbol for joules


mass times acceleration


$$ N = kg * (m/s)^2 $$