|Yes, the falling climber accumulates more energy further they fall. Once the rope tightens over the last piece of gear, the rope acts elastically and stretches. This produces tension in the rope, measured in newtons, both to the climber and the belayer. The more energy the climber has, the more the rope stretches (standard elastic medium process, energy and deformation), resulting in the rope catching them over a longer distance and time. Together this combines to give the force that catches the falling climber and pulls the belayer upwards (which is another part in catching the faller, the transfer of energy to the belayer and loss as friction around the biner). Two tensions along the rope are balanced by the tension that can be considered to be created within the gear wires/transferred to the head of the nut/etc, and this is the force that is the rating they need to hold. The total peak forces are determined by the stretchiness of the rope and in turn how long the fall is caught over, hence stretchier ropes = softer catches, less forces on gear. And i think its more the rope that absorbs the energy, so they could possibly recieve a kJ rating, but i guess it may be irrelevant because there are so many other factors involved/ropes can hold more than the energy possibly created? There are details here i dont understand, but hopefully that should help.