Important Defintions (:

Pressure: the continuous physical force exerted on or against an object by something in contact with it. (Oxford American Dictionaries)

PSI: pounds per square inch (Google Dictionary)

Center of mass: mass center is the mean location of all the mass in a system (Google Dictionary)

Propulsion: the action of driving or pushing forward (Oxford American Dictionaries)

Newtons 1^st law: a body remains at rest or in motion with a constant velocity unless acted upon by an external force (www.astronomynotes.com/glossary/glossn.htm)

Newtons 2^nd law: the amount of force needed to cause an acceleration depends on an object's mass, such that the force applied = the mass of an object × its acceleration (www.astronomynotes.com/glossary/glossn.htm)

Newtons 3^rd law: for every action force ON an object, there is an equal but opposite force BY the object. (www.astronomynotes.com/glossary/glossn.htm)