Similarly, it was shown that the kinetic energy induced in the accelerated matter resulted in the increase of mass from that at rest to that at the achieved spatial velocity, and this was referred to as energy mass.

Finally, it was shown that the two spatial reaction terms resulting from the applied force, combine to produce a further apparent increase in mass of the accelerated matter, and this was equated to inertial mass. All of these concepts are examined here within the gravitational Relativistic Space-Time Domain D₁. The examination is conducted for motion which is (i) purely gravitational, and, (ii) where the gravitational motion is augmented by an artificially applied force.

Note that a term will only be defined in this paper if it has not previously been so in either [1] or [2] with which familiarity is assumed.

Similar to the case of forced motion in D₀, the reaction forces induced in a gravitationally accelerated mass in D₁ can be seen from [1] Eq.(3.2), to consist of four components. The analysis of these terms can be simplified, without any loss of generality, by considering simple rectilinear motion only, and the rectilinear version of [1] Eq.(3.2) can be obtained by putting w to zero, to obtain

where F_g represents the internally generated accelerative force of gravitation and all other terms are as defined in [1].

Clearly, (2.1) contains four reaction terms, two spatial and two temporal and, in the same manner as in [2] Fig. (3.1), these reaction forces can be expressed in relation to the Existence Velocity Vector of the gravitating mass as shown in Fig. 2.1 below

where in Fig. 2.1, F_e represents the component of F_g along the Existence Velocity Vector of the gravitating mass and F_a the component transverse to it.

From (2.1) and Fig. (2.1) it is clear that

and F_a therefore relates the energy mass to the time rate of change of the Existence Velocity Vector.

Similarly

and thus F_e relates the Existence Velocity Vector to the time rate of change of energy mass.

From (2.2) and (2.3), following the same process as in [2], the balanced force vector diagram for gravitational rectilinear motion can be established as in Fig. 2.2 below

Accordingly, as in [2], the four reaction terms can be defined as follows

The above results are very similar to those obtained in [2] for the analysis of forced motion in D₀. However, there is one very significant difference. This is the manner in which the motion is driven. In D₀ it is due to the application of an external force to produce an acceleration proportional to the applied force and the inertial mass of the accelerated body. In D₁ the motion is driven by the action of the Acceleration Potential of D₁ on the gravitating mass, to produce an internally generated accelerative force proportional to the energy mass of the gravitating body. This difference has important implications concerning the mass and energy of the gravitating mass which are analysed in depth in the following Section.

It is also noted that, as in D₀, the temporal terms are equal in magnitude but opposite in sign and therefore cancel. This is confirmed by additional analysis in the next Section.