How to Measure Speed in Java?

Greetings, everyone. Before I explain the title, I just want to introduce what I'm trying to do:

I have a series of images. Mostly a body with two arms. It responds to the movement of the mouse. When the mouse moves, I want the arms to rotate backwards, as if dealing with a lot of air resistance. I have no problems with the rotation, the only issue is I want the arms to flail back more and more the faster the mouse is moving.. But then, how do I measure the speed of the mouse? Is there a way to measure how much pixels the mouse is covering when it moves over a certain amount of time? Or is there another method to get different results of an action to occur when dealing with various speeds of MouseMotion movement?

I hope this isn't too vague. If you need any clarifications in order to help me out with this issue, feel free to let me know

The mouse's position and the time the mouse was at that position should allow you to compute a speed:
change in position/change in time.
The System class has a method that returns the current system time.