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It's relatively common knowledge that when one kicks a football, if they lean back the ball usually goes higher, and if they lean forward slightly it goes at a more desirable height.

Why does leaning back make the ball go higher?

I'm guessing that it could be something to do with the centre of mass or angular momentum.

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This is likely a question about sports physiology and bio-mechanics rather than one about physics. Obviously those topics can be described in terms of physics, but they are generally treated by specialists. –  dmckee Nov 11 '12 at 18:56
    
Where do you suggest I migrate to? –  Olly Price Nov 11 '12 at 22:10
    
I don't suggest migrating it at all, and don't know of a Stack Exchange site where you will necessarily find a good answer. I'm just saying that it is not clear that there is a concise answer in term of basic physics. Question involving how people move are generally complicated. –  dmckee Nov 11 '12 at 22:14

2 Answers 2

Your leg moves within certain angles of displacement - back and forth - with respect to your torso (which the leg is "mounted to").

On the other hand, the angle the ball will go (the hight above the court) depends on the angle your leg assumes at the last moment of contact (the greater the angle, the higher above the ground the foot goes and the higher the ball will go).

Now, if you lean back, the same movement of your leg - wrt. your torso - will result in your foot going higher above the ground (notice that if you are just lying back on the ground and kick the ball, you will find it impossible to kick a ball in parallel to the ground unless you kick it with only the tip of your shoe - if you kick the ball with the upper part of your foot the ball will always go up).

To sum up - leaning back changes the angle of your torso with respect to the ground, which changes the hight your foot will naturally go when kicking the ball, which makes it go higher.

By the way - how high the ball goes depends also where, relative to your body, the ball is at the moment of kicking. If it is just next to your leg you are standing on, it will tend to go low above the ground, but if it is further in front of you it will rather go higher. This is so for the same reason as your initial question - angle.

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When lean back you're foot naturally goes a little bit higher. Try it, just lift one foot like 5 cm of the floor, and then tilt back and forth and you will see that you're foot will go along. When you hit a football every mm counts.

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