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Comment by kccqzy | Hacker News Reader

I hate the weasel words of "demands slowing down". It's always not clear what exactly is happening from this phrase. Is the production or sales going down year-over-year or quarter-over-quarter? Because that's what people think "demand slowing down" means.

However what's actually happening is that demand is going up, but at a rate slower than before. Imagine that in 2022 demand increased by 60% YoY but in 2023 demand only increased by 40% YoY (these are approximate figures). You are measuring the second derivative which is decreasing from a big positive value to a smaller positive value, which is not usually described by the word "slow". Intuitively "slow" means the second derivative has become negative.

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It's worst than that : the 40% are bigger that the 60% of the previous year in absolute value (100 => 160 => 224). It's not even slowing down.

So the rate of change of demand is decreasing. Decreasing rate of change is the definition slowing down. Although I agree that most people probably misinterpret the phrase as you say. (It seems other replies have had that interpretation.)

Increasing less fast is not the definition of slowing down, it's the definition of increase increasing less fast.

> Increasing less fast is not the definition of slowing down

Increasing position less fast is the definition of slowing down, as I said. Increasing speed less fast is, of course, not the definition of slowing down, it's decelerating; we agree on this.

But you are equating demand to "speed" (rate-of-change of position), and I am equating demand to "position" (not a rate-of-change). If demand is analogous to speed, then what is is measuring the rate-of-change of?

If you reduce acceleration, your speed is still increasing if you still have positive acceleration. This is still speeding up, not slowing down.

If rate-of-change of demand is acceleration, that means demand itself is speed and is measuring a rate-of-change. What is demand measuring the rate of change of?

Acceleration decreased such that it is negative. Negative acceleration is "slowing down."

> demand itself is speed

Ok, let’s substitute that into the original comment, instead of:

> demand has slowed down recently

we get:

> speed has slowed down recently

Nothing to do with the rate of change of speed, just speed itself. In other words:

In terms of _speed_, this would indicate that _speed_ was once higher and is now lower.

Let’s translate that same sentence back substituting speed with demand:

In terms of _demand_, this would indicate that _demand_ was once higher and is now lower.

That statement cannot be true as 2023 demand was the highest ever.

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.

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