Many “truthers” often misuse the term “ speed of gravity” in a futile effort to sound knowledgeable, such as the statement “ the towers fell at the speed of gravity.”
The problem is, speed of gravity has to do with two astronomical bodies, such as the sun and the earth. Refer to Wikipedia and you will get this definition of the speed of gravity: “In the context of classical theories of gravitation, the speed of gravity refers to the speed at which a gravitational field propagates. This is the speed at which changes in the distribution of energy and momentum result in noticeable changes in the gravitational field which they produce.”
In layman’s terms, this means the length of time it takes the effect of the gravity of object A to reach and affect object B.
As we see here, although there is still some debate, the first test of the speed of gravity, which occurred in January of 2003, indicates that the speed of gravity is about the same as the speed of light.
The speed of gravity is NOT the same as acceleration due to gravity, which, for the Earth, is 9.8 meters/second/second ( m/s2) or, in the English system of measurement, 32 ft/s2 (source).
Now, let’s review some real world physics- speed and acceleration are NOT the same thing- in point of fact, as any physics book will tell you, speed and velocity are NOT the same either. 75 miles per hour is speed, 75 miles per hour due north is velocity. Simply put, velocity has direction, speed doesn’t.
Getting back to acceleration and velocity, they are NOT the same either. Physics defines acceleration as a change in velocity over time- this means velocity is a COMPONENT of acceleration.
Now, again, mass does not move mass, force does as per Newton’s First Law of Motion, and since Newton’s Second Law of Motion states that force = mass times acceleration ( F = ma), then it’s obvious to anyone who understands real world physics that the outside force came from the planes; after all, the planes had mass and it’s pretty obvious that a speeding plane slamming into a building will experience a rather abrupt change in velocity.
Newton’s Second Law also applies to the upper floors of the WTC hitting the lower floors. Until the upper floors impacted the lower floors, the lower floors had no force since F = ma and acceleration requires motion.
Now before some “truther” brings up Newton’s Third Law of Motion, which states, “ All forces occur in pairs, and these two forces are equal in magnitude and opposite in direction,” or “For every action there is an equal, but opposite, reaction” ( source), Newton’s Third Law applies to TWO objects. Yes, the upper floors and lower floors would be two objects but you had a third object in the mix too. That third object would be the earth via gravity.
Now, getting back to the issue of the speed of gravity, the only way for that to have an effect is for the earth’s gravitational field to suddenly fluctuate due to some sort of gravitational anomaly and a distance between the two objects for said fluctuation to traverse, which would have caused some rather nasty tectonic effects, such as tidal waves, massive earthquakes, etc. I don’t recall any of those occurring on 9/11/01, so clearly, there was no gravitational anomaly- this isn’t Captain Jonathon Archer’s Enterprise cruising through the Expanse.
Truthers are Sanity Challenged 