Detailed Instructions: Given a scientific passage and an answer, generate a question for the given answer.
Q: Passage: In everyday conversation, to accelerate means to speed up. The accelerator in a car can in fact cause it to speed up. The greater the acceleration, the greater the change in velocity over a given time. The formal definition of acceleration is consistent with these notions, but more inclusive. Average Acceleration Average Acceleration is the rate at which velocity changes,. Answer: velocity
A:
In scientific terms, average acceleration is the rate at which what changes?