RPM of a football

  • #1
looking for some guidance on what seems to be an oversimplification of calculating RPM. Using hi speed video (240 frames per second), I can determine that it takes .087 of a second for a thrown football to make its first revolution when coming off the hand of the thrower. Assuming I want to use this time for 1 minute, I get an RPM of 689.65. Does this sound correct? TIA
 

Answers and Replies

  • #2
DrClaude
Mentor
7,607
4,009
looking for some guidance on what seems to be an oversimplification of calculating RPM. Using hi speed video (240 frames per second), I can determine that it takes .087 of a second for a thrown football to make its first revolution when coming off the hand of the thrower. Assuming I want to use this time for 1 minute, I get an RPM of 689.65. Does this sound correct? TIA
Yes. If you divide 60 s by the time in seconds it takes to make une revolution, you end up with RPM.
 
  • Like
Likes BonBonBrady and Delta2
  • #3
35,123
6,864
Alternatively, if you work with the units involved, it might be easier to follow.
Given information: ##.087 \frac{\text{sec}}{\text{revolution}}##
This is equivalent to ##\frac 1 {.087} \frac{\text{revolution}}{\text{sec}} = \frac 1 {.087} \frac{\text{revolution}}{\text{sec}} \cdot 60 \frac {\text{sec}}{\text{min}}##
The last factor converts seconds to minutes, and the resulting units are revolutions/min = RPM, with the seconds units cancelling.
Multiplying 60 by 1/.087 is equivalent to dividing 60 by .087, which is what @DrClaude suggested.
 
  • #4
Vanadium 50
Staff Emeritus
Science Advisor
Education Advisor
27,204
11,167
I get an RPM of 689.65.

Probably this is 690. When you wrote 689.65 you are saying it's more than 689.645 and less than 689.655. You probably don't know it this accurately.
 
  • #6
Office_Shredder
Staff Emeritus
Science Advisor
Gold Member
4,622
630
I would have thought a professional quarterback would get a lot more spin than a random person. Maybe it slows down pretty quickly after release?
 
  • #7
berkeman
Mentor
59,933
10,142
I would have thought a professional quarterback would get a lot more spin than a random person. Maybe it slows down pretty quickly after release?
I don't think so on either point. Even an amateur can throw a football 50 yards/meters, so the force of the throw and the corresponding release and release RPM would be similar. The difference with good quarterbacks in my experience is the much better alignment of the spin with the launch angle (no wobble) and much better accuracy of the launch path.

However, there is a very big difference in baseball backspin RPM between the casual baseball player and a trained high school / college / professional player, since we are taught to maximize backspin on the ball on our throws. We learn to always pull the ball out of our glove with our fingers in the "4-seam fastball" position, so we can whip the back of the ball down as we throw to maximize backspin and minimize the drop of the ball. I learned that in high school from our semi-pro baseball coach, and spent hours at home in front of the TV tossing a baseball into my glove and learning to always grab it in the 4-seam position. Thanks coach! :smile:
 
Last edited:

Related Threads on RPM of a football

  • Last Post
Replies
12
Views
2K
Replies
7
Views
2K
  • Last Post
Replies
5
Views
4K
Replies
1
Views
544
Replies
18
Views
26K
Replies
7
Views
420
  • Last Post
Replies
18
Views
3K
  • Last Post
Replies
3
Views
1K
  • Last Post
Replies
3
Views
10K
  • Last Post
Replies
1
Views
963
Top