In high school, I was tray sledding with a bunch of my buddies on campus, when we spied a group of elementary kids walking toward our hill. One of my friends packed a snowball and hucked it straight up into the air. It was one of those moments where you half-intend a result, but never expect that it will actually happen. We watched with amusement as it sailed straight up, tracked it as the force of gravity overcame its upward velocity, sending it plummeting back to earth, and all stood mouth agape as that snowball accellerated at 9.81 m/s2 until it met the equal and opposite force of the top of some poor 3rd grader's head, 20 yards away.
Now I have two such moments. I have Airsoft guns to thank for this.