This is an extract of "Appendix A" in my manuscript on a new theory which can be accessed through the link in my profile if someone would be interested. The real Equation of Force is F = ma Today's Physics is stating that the Equation of Force is F = dp/dt. We will analyze the equation of motion of rockets to see that the real Equation of Force is: F = ma A rocket has variable mass in its trajectory and it's important to see its motion equation. Let m be its variable mass at any instant in its movement composed by the mass of the rocket plus the mass of its contained fuel. I have made a search in the internet about rocket motion equations and all the sites agree in the equation: F = m(dv/dt) = –ve(dm/dt) where ve is the speed of the fuel expelled relative to a frame at rest. One web site: http://www.braeunig.us/space/propuls.htm They all agree that the force acting on the rocket is due to the expelled mass and is F = –ve(dm/dt) and that the equation of motion is F = m(dv/dt) = ma. I assume the equation have been completely verified experimentally with enough precision from a long time ago. It is evident that it is used the equation: F = ma for the force and not: F = dp/dt ... ... … This indicates that today's Physics is wrong stating the Equation of Force as F = dp/dt. The right equation for force is F = ma even when mass varies. Note that the natural derivation of the famous equation E = mc2 by Relativity Theory has no sense since it is based in the wrong relation F = dp/dt. Relativity Theory becomes a wrong theory since it is based on a wrong law.