How do you turn a proportionality between variables into an equation?

Answer. By adding the proportionality constant .

Explanation:

suppose 'x' a  is directly proportional to the 'y' , where x and y are variables:

x ∝ y

with an input of constant value 'K' proportionality relation gets converted into  an equation:

x = K y

For example : Gravitational force is directly proportional to the product of two masses and inversely proportional to the square of the distance between the two masses.

F ∝

To convert this proportionality relation constant 'G'  was introduced known as gravitational constant whose value remains constant under every conditions.

radioactive decay occurs in unstable atomic nuclei – that is, ones that don't have enough binding energy to hold

the nucleus together due to an excess of either protons or neutrons.

c, liquids evaporate, creating a gas