We have talked about the basic unit of mass as the kg. The basic unit of force is the Newton and the size of the force may be stated in newtons. Every object is pulled to the earth by a force called gravity.
On carth a 1 kg mass is pulled down by a force of approximately 10 newtons. The force gravity on 1 kg mass is equal to 10 newtons. If a person hava a massol of 75 kg a force of 750 newtons is exerted on that mass at the surface of the earth.

PRESSURE

Pressure is the force exerted over an area of contact:

In drilling we are concerned with a number of forms of pressure, including the pressures necessary for crusging or fracturing rock, as well as liquid and water pressures for various applications.
In the English system, we may use psi to describe the pressure of a fluid such as air or mud, or lb/ft2 to describe loading on a jack-pad.