PSM5

Are you familiar with the standard gravitational parameter? It doesn't have units of force, but it is a direct measure of a body's "gravitational charge".

Yes, I was agreeing with him on that point. I agree with your post. However, I would just like to add that the use of the term passive gravitational mass in the universal law of gravitation is just a convention. It is not necessary. The split of gravitational mass into it's current two forms, active and passive, did not even exist before 1957. For example, when you apply Newton's second law to the universal law of gravitation to get the acceleration of mp, you are canceling out the passive gravitational mass mp in the universal law of gravitation with the inertial mass mi in Newton's second law. If they were not the same then you should not be able to do this. Having three different types of mass can be quite confusing.

It's not really necessary. It just makes the units come out right. If units are not important for what you're trying to show then you can just set it's value to 1 and leave it out. An example is this wikipedia page showing the proportional equivalence of the three types of mass: http://en.wikipedia.org/wiki/Equivalence_principle#Active.2C_passive.2C_and_inertial_masses As juanrga pointed out, there is another way to look at this. However, I'm not sure if this would be an academically correct way of looking at it. And that way is to consider the value of G to be a constant of proportionallity between active gravitational mass and inertial mass. For example, if two universes (A and B) were identical in every way except one had a higher or lower measured value of G than the other, then the gravitational force between two bodies in A and the gravitational force between two bodies in B would be different, even though the inertial masses of all four bodies were the same. In other words, G determines how strong the gravitaional field is for any particular unit of inertial mass.

Both of Janus's scenarios are technically correct. I will try. The first is called the universality of free fall. It is the acceleration of either body (the earth or the falling object) relative to their common center of mass. [math]A_{m1}=\frac{Gm2}{r^2}[/math] [math]A_{m2}=-\frac{Gm1}{r^2}[/math] The second is called the relative acceleration. It is the acceleration of either body relative to the other. [math]A_{rel}=\frac{G(m1+m2)}{r^2}[/math] The difference between the two scenarios is only in the frame of reference. The time to impact will be the same either way. I think the reason Janus declaired the first scenario to be a more technical usage is because the frame of reference for the first scenario is inertial, the second is not.

Okay, I think I'm understanding your thought experiment now. I'm just not sure how it relates to the equivalence principle proper. Your OP claim that there is a difference between the acceleration of an object in free fall and an accelerating rocket is true for macroscopic objects. From the same Wikipedia page that you linked: I have read some text that claim the equivalence principle applies only to point masses. But that was not part of Einstein's original.

That's the part I don't understand.

The equivalence principle applies only to point masses. What if the accelerating rocket were rotating? What would be it's direction? The milky way galaxy rotates, so how can you know that the rocket is not rotating?