Electric Charge andStatic ElectricityIt was known as early as 600BCEthat objects could become charged by rubbing fur on various substances such as amber. Charged objects could be used to attract light objects such as hair. In the 1700s, it was determined that charge came in two varieties that could cancel each other out. Charles-Augustin de Coulomb established a quantitativerelation in 1783 that describes how charged objects interact via the electric force. The electric force:

Explanation:

In 1785, Coulomb investigated quantitatively, the force exerted between point charges.

The Coulomb's Law states that: "The force of attraction or repulsion between two, point charges is directly proportional to the product of magnitude of the charges and inversely proportional to the square of the distance between them. "

If q₁ and q₂ are two, point charges and r is the distance between them, then the electric force of attraction or repulsion F between them, according to Coulomb’s law will be:

F∝q₁q₂ eqn (1)

F∝1/r²   eqn (2)

Combining eqn (1) and eqn (2), we get:

F∝(q₁ q₂)/r²  

F=(kq₁q₂)/r²  

where,

k = constant of proportionality = 9 x 10⁹ N.m² / C²

the device is called “ rocket engine”