The other day I was watching a soccer game, West Ham United vs Arsenal FC. I know I do blogs on soccer all the time but it's because I am just so fascinated by the things these players are able to do, hence why they are professionals. One of the players, Andy Carroll scored a bicycle kick, where a player flips himself/herself upside down with their foot in the air and kicking it over their head (sometimes referred to as an "overhead kick"). While this one was good, it reminded me of one from several years ago that another professional, Wayne Rooney performed in a game. Here's the video:
While this goal may still have you in awe (this happens maybe once every several years by the way), I'd like to start talking about the physics. So it all started with the crosser, Nani, who crossed the ball in at about 22 mph (the speed of an average cross). This speed of the ball means the reaction window for Rooney was microscopic, even to just put the ball on target - much less the upper corner of the net. A half second too quick or too slow and this bicycle kick will end up on the blooper section of sportcenter. Upon timing the jump, Rooney is in the air for about 3/4 of a second, meaning the margin for error is quite small. Rooney's foot has also been measured to be 1.80 meters above the ground (5'9") which is about the same height as Rooney. So you might ask, what is the advantage of doing this if he could've headed the ball instead? While this is normally what players do in this scenario, a header simply wouldn't have provided the same force (and thus acceleration) on the ball. This is because of the net torque on the ball. With a header, one really only uses a little less than half of their body to cock back and snap into the header to deliver a net force upon it. However, with a bicycle kick the whole body is involved. Since the body in midair experiences no outside forces, it acts as if it were a rotating object, where both halves of the body contribute to a clockwise motion to allow a well powered kick.
In addition, you will notice that he kicks one leg first and then the other. This has to do with momentum. as he generates momentum in one direction, this allows him to change the motion with the other leg and allow a greater velocity with his kicking leg before it makes contact with the ball.
All in all this stands as one of the best premier league goals of all time, ask anybody. It's really cool now to understand how Rooney did this (I know I never could)