You will be given a definition of a task first, then an example. Follow the example to solve a new instance of the task.
Given scientific fact as input, generate the question from this fact such that it can be answered from the input.

Earth rotates on its axis once times in one day.
Solution: How many times does Earth rotate on its axis in one day?
Why? The given output correctly poses a question based on the scientific fact given.

New input: In a longitudinal wave, amplitude term is a measure of how compressed particles of the medium become when the wave passes through.
Solution:
In a longitudinal wave, what term is a measure of how compressed particles of the medium become when the wave passes through?