Acceleration

So, N acts as my Physics Class lab partner. Geeky but true, we have spent several pleasant Saturdays with weights, measurements, and time intervals. The lab requirements are generally tasks such as:

Drop this box from a great height and time how long it takes for the box to crash to the floor. Now repeat this task with your eyes closed.

-or-

Weigh this bolt from a spring scale as it dangles in the air, now take another weight measurement as the bolt is suspended in water.

Today we were studying acceleration. I was tasked with throwing a tennis ball as fast and as hard as I could, her job was to operate the stop watch to record how fast the ball traveled various distances. Well, I'm not so great with aim and on one time trial I pegged my kid in the arm with the ball. We both gasped with shock.

"Youch," she squealed.
"Oh, God are you OK?"
"Yeh. Yeh, mom, you'll have to do that one again. I forgot to hit the stop button."