Why is speed and dwell time not a linear relationship?

I've just gone through the exercise of converting a dwell time on a conveyor to an effective motor speed to achieve that dwell time. During this process, I realised that the relationship is a "to the power of" equation, not linear. My calculation is working, with the formula y=ax^b, where y=motor speed, x=dwell time, and a & b are constants (b = -1). But everything in my brain keeps insisting that the relationship should be linear.

Even working it out theoretically give me the same result. Assume that a motor speed of 10Hz yields a dwell time of 60 minutes. If you double the speed of the conveyor, the dwell time must halve. So, 10Hz=60min, 20Hz=30min, 40Hz=15min, 80Hz=7.5min, 160Hz=3.75min. If you put those values into excel and plot them, then draw a line of best fit, it's a power-of relationship clear as day.

But I don't understand why. Any math geeks out there that can help explain it to me in a way that I understand?

Just realised I had my axes the wrong way around. Doesn't change the outcome.

Speed (m/s) = distance (m) / time (s)

x^-1 = 1/x

Worked it out just now with the help of some rubber duck* debugging. Spot on, Ian.

v=d/t which is a linear relationship when distance is one of the variables. When distance is fixed at say 600 units, then the equation is v=600/t, which can also be represented as v=600t^-1