Earlier quoted context omitted.
I think you misread my comment. Demand is not analogous to speed, it's analogous to position. I was asking how you were relating demand to speed, in your comment. It may be easier if you start using "rate-of-change of demand" instead of speed.
When we talk about supply and demand for cars, it has a time element. Units per year, units per quarter and so on. It is analogous to speed. Doing anything else would make it impossible to plan the supply chain. Where it could be different is in places like power generation. You might talk about peak demand in Watts, and daily demand in watt-hours.
I see. Then, if demand is the rate of... demand (?), it is analogous to speed and it's not appropriate to say "slowing down", as you say.