Train mass and momentum
Heavier trains carry more momentum — loads and empty seats can change feel slightly.
Momentum is mass × velocity. A full train has more momentum than an empty test run — launches may be tuned for loaded conditions.
More mass does not automatically mean faster, but it can carry through elements with less perceived slowdown if energy is high.
Wind and temperature interact with mass too — light trains on windy days face more relative air drag.
This is one reason enthusiast “test seat” rides before a busy day can feel subtly different from a packed train at dusk.