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Old 25-08-2010, 12:30 AM
ho chi feen ho chi feen is offline
Join Date: May 2003
Location: Vigo, Spain
Posts: 27,176
Talking Can footballers REALLY hang in the air?

Tch, they should have come here, we dealt with this number AGES ago...

"Just finished watching Match of the Day and something struck me about one of the pundits comments," begins Pieter Nicholls. "Arsenal's Marouane Chamakh was described as 'hanging in the air' before heading a corner at goal. It's something that's often said of footballers, but is it actually possible?"

The Knowledge dropped one of its closest chums an email and, hey presto: "Once a player has jumped, in the absence of wings or any other means of generating a thrust, then the centre of gravity must be decelerating due to gravity at all times during the jump," explains Dr Tony Weidberg of St John's College. "The centre of gravity is initially going up, slows down and then starts coming down. So I have two possible explanations:
1) around the time in which the velocity of the centre of mass in the vertical direction goes through 0, the velocity will be very low. So there might be a short period of time in which the eye can not resolve any vertical motion.

2) The force of gravity only requires that the centre of mass is decelerating but if the player is also rotating, it would be possible for the centre of mass to be falling but the head might be held at constant height for a period of time. If the eye was focussing on the head, this would generate an illusion of the player floating.
I don't really know if either of these explanations is correct and it might all be just an illusion ..."

Best get a second opinion. Here's Alan Barr. lecturer in particle physics in the University of Oxford's department of physics. "Tony is quite right that (leaving rocket boosters, wings and wires aside) the centre of gravity of the player - loosely speaking the 'average' position of his or her body - has to continually accelerate downwards. Galileo and Newton told us that a long time ago, and that physics hasn't changed.

"But that necessarily doesn't mean that the floating has to be an illusion. If you watch the 'floating' player, you'll often find that towards the top of his jump he forces his arms and legs down hard. Why does he do this? The limbs are not used to hit the ball but in fact as any coach will tell you, they are still very important in the action. If the player can make these 'extraneous' limbs move down fast, then the average position of his body will accelerate downwards (as demanded by friend Newton), while the important bits for the header his trunk and head hang in the air.

"So the arms and legs play an important role in moving the rest of the body during headers as a bit of slow-mo replay will show. In fact the other noticeable movement of the arms from "in front" of to 'behind' the player is there for a similar reason. By pulling his arms backwards his trunk and head moves forwards, and his head hits the ball harder. If you go through the motions of a header yourself and you'll probably find that you naturally move your arms fast from an up-and-forward position to a down-and-backward one. Physics tells us why this makes sense, but to the average player it's just a natural movement."
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