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Thread: When do i get the hardest shot when i play football (Soccer

  1. #1 When do i get the hardest shot when i play football (Soccer 
    Forum Freshman Carbon's Avatar
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    When do i get the hardest shot when i play football (Soccer)?

    Is it harder when the ball is quite still?


    Or is it harder when it's rolling towards you?


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    Forum Masters Degree organic god's Avatar
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    well momentum is a vector quantity.

    so for the ball to have the greatest momentum it would be with the ball standing still assuming your foot had the same momentum each time you struck the ball.


    everything is mathematical.
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    Quote Originally Posted by organic god
    well momentum is a vector quantity.

    so for the ball to have the greatest momentum it would be with the ball standing still assuming your foot had the same momentum each time you struck the ball.
    This would be true if the collision were inelastic. Then you would just use conservation of momentum. The foot would have momentum equal to its mass times its velocity. The ball would have momentum in the opposite direction equal to its mass times its velocity. The combined mass would have momentum equal to the sum of the masses multiplied by the velocity of the two masses stuck together after the collision.

    This collision would be mostly elastic, I think. For elastic collisions you have to use conservation of energy, too. The final velocity of the foot is different than the ball. I don't have time to work it out now. Maybe later.
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    Every footballer knows you get a harder shot when the ball is moving toward you. The same is true in baseball, in which a fast pitch will be hit further than a slow pitch, which is still hit even further than a motionless ball.

    The answer has to do with the fact that the foot (or bat) is much heavier than the ball. Therefore the incoming momentum of the ball is transferred to itself for the shot.

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  6. #5  
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    It would seem that the more momentum transferred to the ball, the further the ball will travel. P=mv.
    Religious Fundamentalist Club - Member #1.
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  7. #6  
    Time Lord
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    Quote Originally Posted by SteveF
    Every footballer knows you get a harder shot when the ball is moving toward you.
    It's true. Why?

    Quote Originally Posted by Harold14370
    For elastic collisions you have to use conservation of energy, too.
    We can think of the ball as a spring that can't be much compressed by the limited speed of a kick. When the ball hits the foot we gain extra compression, while inertia of the leg is great enough to accelerate the ball just as well anyway. So the ball has stored up extra elastic energy, that continues to accelerate the ball in parting with the foot.
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    This article explains the math of an elastic collision.

    http://en.wikipedia.org/wiki/Elastic_collision

    If you scroll about half way down the page, there is an animation called "Elastic collision of unequal masses" which shows two bodies of equal and opposite velocity colliding, one twice the mass of the other. The lighter mass (analogous to the ball) comes away with a speed of 5/3 its initial speed while the heavier mass (which would be like the foot) recoils at 1/3 its initial speed.

    That's not what really happens when you kick a ball. Your leg keeps going in the same direction. That could be either because it is more than twice the weight of the ball or because the collision is partly inelastic.
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    I once saw a TV programme in which Bobby Charlton ( ex Manchester United striker who could score goals from 40 yards out) spoke about this. Apparently he spent hours kicking a ball against a wall trying to"hit it right". It seemed that what he was talking about was striking the ball when his foot was moving at the highest speed. The foot accelerates and then decelerates. "Hitting it right" appears to involve striking the ball when the foot is moving at maximum speed. The player has no control over the speed at which the ball is moving before he hits it. However, I would agree with those who maintain that the ball would move more quickly if it was initially stationary rather than moving towards the player.
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  10. #9  
    Forum Freshman Faldo_Elrith's Avatar
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    When the ball is moving towards you, the relative velocity between foot and ball is greater than when you're kicking a stationary ball. This allows you to kick the ball harder.
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    Quote Originally Posted by Faldo_Elrith
    When the ball is moving towards you, the relative velocity between foot and ball is greater than when you're kicking a stationary ball. This allows you to kick the ball harder.

    There are exceptions. When playing kick ball, with a rubber ball. If spin is put on the ball. Similar to the spin on a bowling ball. When you connect to the ball, the ball jams against the surface. If the surface can cause friction. Like an asphalt surface.

    I knew a kid that would put the strangest spin on the kickball when serving it up to you. I had a lot of trouble getting it off the ground. Yet a stationary ball, I could put right up into the air everytime. Or if other kids would serve it, then I could put it into the air.

    It was a very interesting thing.

    Sincerely,


    William McCormick
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  12. #11  
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    Quote Originally Posted by Old Fool
    "Hitting it right" appears to involve striking the ball when the foot is moving at maximum speed.
    There is that, but also each ball has an ideal period of rebound, and will continue to reverberate (at high frequency! e.g. the sound it makes) so you want the kick to follow through such that the ball is springing away with greatest energy in parting from the foot. Why any ball "will do" but you have to get a "feel" for it.

    Brute force is the main thing but finesse matters.

    I think we all know how a bar of soap dropped into the tub will make different waves depending on how it hits the water - the fastest impact does not make the greatest waves.
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