In motion studies, the point in space and time at which motion begins is selected as the origin.

Here's why:

* Space: The origin serves as a reference point for all spatial measurements. It's like setting a "zero" on a ruler.

* Time: The origin marks the starting point for the analysis of the motion's duration.

Think of it like this: if you're studying the motion of a car, you would choose the spot where the car starts its journey as the origin. From that point, you can track its position, velocity, and acceleration over time.