RobbieB said:
Mostly for coaches/proshop gurus to think about...
If a bowler has a free swing- ie, no muscle tension/acceleration in the swing - what effect do the following changes have on ball speed and why?
1- Raising or lowering the position of the ball in the stance;
2- Increasing/decreasing ball weight.
Cheers, Robbie.
Ooo... What a good geeky question! It's like when two trains leave at the same time and so on... I suspect that you're seeing just how far down this rabbit hole we go, Robbie ;-)
1-Raising or lowering the ball should raise or lower the swing height all things being equal. However, all things aren't equal. The "pendulum" hangs off a moving fulcrum (the shoulder), who's motion is in turn affected by the motion of the pendulum. This is not simple maths, but we won’t need to do the calculus to work out the result.
As the ball swings back, it drags the shoulder back (open), reducing the forward motion of the shoulder and its attached body. As the shoulder only closes in the final moments of the swing as the ball drops to the release point, when the body's forward motion is decreasing toward zero in the slide and the horizontal vector of the swing becomes small enough to overcome for mere mortals, it’s safe to assume that this loss of velocity is not recovered.
Therefore, higher “swing drag” of the body is created by the higher ball position, owing to higher momentum needing to be reversed at the top point of the swing. A ball moving faster backwards takes longer to slow, leading to a higher swing and later timing unless foot cadence is slowed to accommodate the longer swing time.
However, the ball is now set to drop from a higher point. This means that the greater arc of the downswing spends more time in the zone where the vertical component of the swing vector is greater than the horizontal component, meaning that gravity is assisting the acceleration of the ball. This is serious assistance at 9.8 m/s². (Gravity becomes more neutral as the swing bottoms out and becomes more forward than downward.)
Therefore, in an "unmuscled" swing (don’t know, never had one to speak of), the higher ball position leads to a higher backswing peak at the point of the power step than a lower ball position would achieve at the same point in time, so we can safely assume that the long held belief of a higher ball position leading to greater delivery velocity holds true.
In fact if you want to prove it, go to your nearest park and play on the swings. Feel the difference in your velocity swinging from different heights.
2- Increasing/decreasing ball weight. Now this one is trickier.
Increased weight means increased momentum (mass x velocity); therefore more of the aforementioned drag on the body as the ball moves from a backward to forward motion. The energy for this change in direction has to come from somewhere and chances are it comes from your shoulder and torso which are propelled by your legs. Ipso Facto - your body gets slowed down somewhat more by a heavier ball.
What the momentum view of things doesn't take into account is gravity - or why we all get saggy as the years go by. Galileo is said to have dropped spheres of different weights from the top of the leaning tower of Pisa to demonstrate to skeptics that the spheres would strike the ground together. (
http://www.newscientist.com/article/mg14920146.300.html) Assuming that the laws of gravity haven't changed in the last 400 years or so, a heavier ball should in theory fall at the same rate as a lighter ball and likewise rise at the same rate. If you had a truly pendulous swing, no difference to ball speed would occur.
In bowling though, a number of variables come into play.
- Players will either pitch the lighter ball, making it go faster;
- the lighter ball will not push as hard into the lane surface, making it travel faster down the lane;
- or the player will lift or rotate the lighter ball a bit more, as it offers less resistance to the wrist and fingers, making it travel slower down the lane, owing to greater hook.
Difficult to tell what the heavier/lighter ball will do without knowing the individual’s game to be affected by the weight change.
If you're not confused yet. Congratulations. My nerd propeller hat has just about burnt out a bearing on this one...
Cheers,
Jason