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**sherrferris** · 12-03-2010, 06:51 PM

In the wind, I play the ball back a bit in my stance and swing easy. This reduces the height of the flight around 20%. That is usually enough to help it in the wind.

I understand fliers are caused by trapping grass between the ball and the clubface, reducing the spin on the ball. I have had a few while playing in bermuda rough and they are always surprising. I end up checking the club to insure I didn't hit the wrong one as the ball flies over the green like a rocket propelled grenade. This is normally followed by a quizzical WTH!

Most iron shots have backspin on them (more spin with higher lofts) and that backspin causes the ball to rise higher instead of going forward. That is why iron shot look like they fall straight down out of the sky. The spin induced rise is overcome by gravity and down they come. Without the spin, the "knuckleball" has nothing to cause it to rise so all that energy goes into distance. At least that is my take on it.

That's pretty close, C-tech.

Here's the technical version:

As far as spin is concerned, there are two common myths about it. One is that grooves cause spin, which they don’t (they can enhance or ensure spin, but they’re not the reason for spin) and the other is that the ball "rides up" the clubface in some way which is not actually true but serves as a practical explanation for what really happens

Ball flight and spin are simply examples of aerodynamics (fluid dynamics, since air is essentially a fluid) and simple Newtonian physics. All three of Newton's laws apply in various ways when it comes to ball flight and the only requirement in terms of equipment is that there be a frictional surface on the clubface (that it is not smooth).

Newton’s First Law (the law of inertia) is responsible for getting the ball moving in the first place, but his Second Law (the law of acceleration) and his Third Law (the law of reciprocal actions) take over in various ways, which ultimately influence ball flight and distance. The process goes something like this:

The law of inertia basically deals with the clubhead in that its movement (force) acts upon a stationary body (the ball) and provides the inertia to get the ball moving from that stationary position. When the ball is struck the ball compresses against the clubface. In the microsecond or so during which this occurs, the inertial force of the moving clubhead is transferred to the ball.
At that point, both the second and third laws come into play. The law of acceleration “the net force on an object is equal to the mass of the object multiplied by its acceleration” provides the momentum, which moves the entire ball and the reaction to the force with which the ball is compressed against the clubface provides the inertia, or the “opposite reaction” and together they both cause the ball to move forward.

Newton’s third law, "To every action there is an equal and opposite reaction", also plays a major role in the ability of the ball to spin. When a ball is compressed against the clubface, it occurs from the bottom up. Let’s say that a clubface is at a 30-degree angle to the ball. The lower portion of the ball comes into contact with the clubface first, is compressed against its surface and is followed by the area above that point continuing upward towards the ball’s equator. When the ball de-compresses, it does so in the opposite way (equal and opposite reaction) and the lower portion of the ball begins to decompress and return to its original state even as the upper portions are still being compressed. Newton’s third and second laws cause this restoration to occur in such a way that the momentum of this de-compression forces the rest of the ball to “follow” the direction of its deformation, taking the mass of the ball with it, which causes the ball to begin to rotate in the direction of this restitution with the same force and speed with which it was deformed and the inertia of this restitution causes the ball to rotate which results in “spin”.

In the case of a club with a shallow loft (like 9-iron), the ball is not profoundly compressed but is compressed over a larger surface area and in a more off-center/non-linear fashion and this results in greater spin because more ball mass has to travel a greater distance to “catch up” with itself in order to return to its spherical shape.
In the case of a 2-iron, the ball is more profoundly compressed (due to the greater and more concentrated momentum generated by the higher clubhead speed) but is compressed over a much smaller and more uniform area more near its equator so that the resulting restitution is more linear. Since the area of distortion is smaller and more concentrated, its mass has a very short distance to travel when the ball “springs back” to it’s original shape, resulting in less spin.

When a flier occurs, all that’s being done is that the water contained in the grass blades is released when the grass is crushed between the ball and the clubface causing the surface of the clubface to become far less frictional and less able to “grab” the ball. Even though the clubface has grooves cut into it which are there to displace this water (just like the treads in a tire), the remaining clubface surface is still wet and is less frictional. This lower friction reduces the ability of the clubface to “grip” the surface of the ball and there is a momentary “slip” in that connection which reduces the ability of the moving clubhead to fully impart its force to the ball which results in less deformation of the ball, which in turn results in less “restitution” which ultimately leads to less spin.

There is still SOME spin, but not as much as if the ball were struck cleanly with a dry clubface. The reduction in spin means that less air is displaced or “piled up” ahead of the ball as it moves through the air and this of course means less resistance so that the ball reacts more purely to inertia and acceleration and generally flies farther because the reduced spin lessens the resistance to its inertia.

(I love talking about this stuff!)

-JP
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12-03-2010, 06:51 PM	#6
sherrferris Join Date Nov 2005 Posts 605 Senior Member	In the wind, I play the ball back a bit in my stance and swing easy. This reduces the height of the flight around 20%. That is usually enough to help it in the wind. I understand fliers are caused by trapping grass between the ball and the clubface, reducing the spin on the ball. I have had a few while playing in bermuda rough and they are always surprising. I end up checking the club to insure I didn't hit the wrong one as the ball flies over the green like a rocket propelled grenade. This is normally followed by a quizzical WTH! Most iron shots have backspin on them (more spin with higher lofts) and that backspin causes the ball to rise higher instead of going forward. That is why iron shot look like they fall straight down out of the sky. The spin induced rise is overcome by gravity and down they come. Without the spin, the "knuckleball" has nothing to cause it to rise so all that energy goes into distance. At least that is my take on it. That's pretty close, C-tech. Here's the technical version: As far as spin is concerned, there are two common myths about it. One is that grooves cause spin, which they don’t (they can enhance or ensure spin, but they’re not the reason for spin) and the other is that the ball "rides up" the clubface in some way which is not actually true but serves as a practical explanation for what really happens Ball flight and spin are simply examples of aerodynamics (fluid dynamics, since air is essentially a fluid) and simple Newtonian physics. All three of Newton's laws apply in various ways when it comes to ball flight and the only requirement in terms of equipment is that there be a frictional surface on the clubface (that it is not smooth). Newton’s First Law (the law of inertia) is responsible for getting the ball moving in the first place, but his Second Law (the law of acceleration) and his Third Law (the law of reciprocal actions) take over in various ways, which ultimately influence ball flight and distance. The process goes something like this: The law of inertia basically deals with the clubhead in that its movement (force) acts upon a stationary body (the ball) and provides the inertia to get the ball moving from that stationary position. When the ball is struck the ball compresses against the clubface. In the microsecond or so during which this occurs, the inertial force of the moving clubhead is transferred to the ball. At that point, both the second and third laws come into play. The law of acceleration “the net force on an object is equal to the mass of the object multiplied by its acceleration” provides the momentum, which moves the entire ball and the reaction to the force with which the ball is compressed against the clubface provides the inertia, or the “opposite reaction” and together they both cause the ball to move forward. Newton’s third law, "To every action there is an equal and opposite reaction", also plays a major role in the ability of the ball to spin. When a ball is compressed against the clubface, it occurs from the bottom up. Let’s say that a clubface is at a 30-degree angle to the ball. The lower portion of the ball comes into contact with the clubface first, is compressed against its surface and is followed by the area above that point continuing upward towards the ball’s equator. When the ball de-compresses, it does so in the opposite way (equal and opposite reaction) and the lower portion of the ball begins to decompress and return to its original state even as the upper portions are still being compressed. Newton’s third and second laws cause this restoration to occur in such a way that the momentum of this de-compression forces the rest of the ball to “follow” the direction of its deformation, taking the mass of the ball with it, which causes the ball to begin to rotate in the direction of this restitution with the same force and speed with which it was deformed and the inertia of this restitution causes the ball to rotate which results in “spin”. In the case of a club with a shallow loft (like 9-iron), the ball is not profoundly compressed but is compressed over a larger surface area and in a more off-center/non-linear fashion and this results in greater spin because more ball mass has to travel a greater distance to “catch up” with itself in order to return to its spherical shape. In the case of a 2-iron, the ball is more profoundly compressed (due to the greater and more concentrated momentum generated by the higher clubhead speed) but is compressed over a much smaller and more uniform area more near its equator so that the resulting restitution is more linear. Since the area of distortion is smaller and more concentrated, its mass has a very short distance to travel when the ball “springs back” to it’s original shape, resulting in less spin. When a flier occurs, all that’s being done is that the water contained in the grass blades is released when the grass is crushed between the ball and the clubface causing the surface of the clubface to become far less frictional and less able to “grab” the ball. Even though the clubface has grooves cut into it which are there to displace this water (just like the treads in a tire), the remaining clubface surface is still wet and is less frictional. This lower friction reduces the ability of the clubface to “grip” the surface of the ball and there is a momentary “slip” in that connection which reduces the ability of the moving clubhead to fully impart its force to the ball which results in less deformation of the ball, which in turn results in less “restitution” which ultimately leads to less spin. There is still SOME spin, but not as much as if the ball were struck cleanly with a dry clubface. The reduction in spin means that less air is displaced or “piled up” ahead of the ball as it moves through the air and this of course means less resistance so that the ball reacts more purely to inertia and acceleration and generally flies farther because the reduced spin lessens the resistance to its inertia. (I love talking about this stuff!) -JP .
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