Topspin Vs Bulletspin, Which is Faster?

[FiveFrameSwing]

3. Regarding the original question posed in this thread: Assuming the ball is released at the same velocity and at the same location, I suspect there is very little difference in the time from release to home plate between topspin and bulletspin. Both pitches lose speed due to air resistance. There is some evidence from MLB data (sliders have a large amount of bulletspin) that the air drag is a tiny bit less on pitches with bulletspin than on other pitches, but the difference is too small to be of much practical significance. The point about there being more sideways or up-down movement on the topspin/sidespin pitch than on the bulletspin pitch is not relevant. The motion along the pitcher-catcher line is independent of any forces in the up-down or sideways direction, a fact that we teach early on in introductory physics classes.

This is an important point. Please clarify.

Given three pitches with different spins ... 1) bullet spin; 2) 6-12 spin; and 3) 12-6 spin ... all released at the same location/height, speed, and initial trajectory .... how would the profiles differ?

 

[coach james]

OK, after some quickee calculations, the spin would have to exceed 4500 rpm (75 rps) for the ball to rise above its initial trajectory.

In Texas they throw 75 rps by 12u.

A rps (rotations per second)... is that a full revolution, 360° turn?

 

[coach james]

If a rise ball is spinning at a perfect 12/6 orientation, with 4 seams, are we counting just one of the laces in a revolution? Who has a rev fire? We've used one once a couple years back, now granted dd was HE then, but I don't believe she ever exceeded 20... now I'm wondering if the rev fire measures rps or total rotations?

 

[FiveFrameSwing]

CJ ... Revfire reports RPS ... Revolutions/Second.

 

[pobguy]

I calculated at 70 mph. Roughly speaking, the magnitude of the upward Magnus force is proportional to the product of the spin rate and the release speed. So, to "rise" requires 75 rps at 70 mph; that translates to 88 rps at 60 mph (etc.)

 

[pobguy]

How do your calculations take into account the differences in the height and shape of seams of various softballs? Do you have a standard softball or seam height that you use in your calculations?

I assumed a "generic" softball weighing 6.5 oz and with 12" circumference. The seam height does matter if you are really trying to get an exact numerical result. I was satisfied with an "order of magnitude" result that shows that it is not humanly possible to make the ball rise above its initial plane. Quite frankly, we don't know enough about the size of the Magnus force to give an answer to better than +/-20%.

 

[pobguy]

A rps (rotations per second)... is that a full revolution, 360° turn?

Yes. .........

 

[pobguy]

This is an important point. Please clarify.

Given three pitches with different spins ... 1) bullet spin; 2) 6-12 spin; and 3) 12-6 spin ... all released at the same location/height, speed, and initial trajectory .... how would the profiles differ?

Don't have time to give you a detailed response right now. However, I do recommend that you look at my "trajectory calculator", Trajectory Calculator. It is an Excel spreadsheet that allows you to do your own trajectory calculations, where you specify the spin, speed, and direction. Be sure to set the mass and circumference to be appropriate for a softball (cells B1,B2) and set the initial distance from home plate to whatever is appropriate (B4). There is a not-too-difficult learning curve, but once you learn you might find it to be a useful tool.

 

[fastpitchdad8]

great stuff pobguy!

 

[pobguy]

CORRECTION: I had earlier said 75 rps was about the spin needed for the ball to rise above its initial plane, assuming 70 mph release speed. I messed up (yes, even physicists do that, more often than you think; but, we are very good at finding our mistakes). It is more like 60 rps, still about twice what RevFire gives for elite players. The numbers for the spin in the slides I posted earlier are not my own numbers. The PITCHf/x system does not measure the spin. It measures the movement and used that to infer the spin, with the aid of a model. I don't recall offhand whether the model that is used is the best one available, so the absolute numbers for spin should be taken with a grain of salt. The numbers for movement are much more reliable.