Thread: Calculations of Momentum P=mv, and Kinetic energy KE=(mv^2)/2 of a racket on shuttle

1. Originally Posted by craigandy
Still don't trust this one because of the other readings I can see but since your so adamant

Vx racket = 1.22m/s
Vx shuttle = 1.83m/s
Ratio = 1.5
lol, definitely something is wrong

2. Lol... yeah, but at least we got a good output to input ratio.

Does the software need an input for frame rate? Because that FHF super slow mo section is very very high frame rate per sec. Meaning that one frame is probably like 1/1000th of a sec.

3. Lol, Yeah it is clearly not FHF real time.
Tried to do quite a few things with regard to frame rates but to no avail. If the video is already in slo mo you can't input the frame rate of the vid into the software for translation, not that i would know what the fhf frame rate is(or maybe you can I don't know the software inside out and there is developer templates). But you can imagine whatever speed he usually hits the shuttle and divide it by 1.5 to get the real time racket speed.

4. Originally Posted by amleto
That is a bad idea because the further the shuttle travels the more air resistance affects the results.
air resistance is always affecting your results no matter what, whether you measure it when the shuttle has travelled more, or just left the bed of the racquet where it has barely travelled

have you incorporated air resistance in your calculations then? if you have been ignoring it, then why not ignore it further?

and it also depends on how hard the shuttle is being spun, if there is any slice component incorporated in the smash, the spin contributes.

5. Originally Posted by vajrasattva
air resistance is always affecting your results no matter what, whether you measure it when the shuttle has travelled more, or just left the bed of the racquet where it has barely travelled

have you incorporated air resistance in your calculations then? if you have been ignoring it, then why not ignore it further?

and it also depends on how hard the shuttle is being spun, if there is any slice component incorporated in the smash, the spin contributes.

The percentage of speed that air resistance subtracts over the first three feet is worth ignoring. It's a very small percent.

6. Originally Posted by amleto
thanks for the info!

Unless you have access to a swing weight app, then just the racket weight and bp will be useful.

Is the software open source?
Just thinking about this point some more. This way of measuring is never going to be accurate enough to start being able to take into account bp racket weight etc etc. Their is nothing to show how much slice is on the shuttle, also we don't know the reduction off center hits make to speed even off by a few mm could be a lot. The video's can show us some things but no point in including racket details etc as the information is not good enough.

I think if you want to compare what racket weight is best, you would be best forgetting about using a shuttle, and just record swings speed of only you(personally) seeing how fast you can swing the different weighted rackets, then use line and lengths formula!

7. Originally Posted by craigandy
Just thinking about this point some more. This way of measuring is never going to be accurate enough to start being able to take into account bp racket weight etc etc. Their is nothing to show how much slice is on the shuttle, also we don't know the reduction off center hits make to speed even off by a few mm could be a lot. The video's can show us some things but no point in including racket details etc as the information is not good enough.

I think if you want to compare what racket weight is best, you would be best forgetting about using a shuttle, and just record swings speed of only you(personally) seeing how fast you can swing the different weighted rackets, then use line and lengths formula!
I suppose... but still a greater m will have more P and KE, although it's a matter of optimizing the m so that you can still swing it at a very high v. Obviously due to differences in our musculature and technique, our individual optimal m and v will vary.

8. Originally Posted by visor
I suppose... but still a greater m will have more P and KE, although it's a matter of optimizing the m so that you can still swing it at a very high v. Obviously due to differences in our musculature and technique, our individual optimal m and v will vary.
lol sorry that was what i was trying to say in that last paragraph. measure your own personal swing speed for each of the rackets the use the appropriate v and m to see what gives you the higher Vs using LL's formula. Any better?

9. But still, let's say I swing fastest with the Arc FB, that doesn't mean that I'll get the fastest smash with it as it has a really low m. Otherwise you'll see everyone using very light rackets.

Somehow m also plays a large role eg for LCW, LD.

10. Originally Posted by visor
But still, let's say I swing fastest with the Arc FB, that doesn't mean that I'll get the fastest smash with it as it has a really low m. Otherwise you'll see everyone using very light rackets.

Somehow m also plays a large role eg for LCW, LD.
correct just because you swing fastest doesn't mean fastest smash but that's why you need to use line & length's formula as stated.

So for instance lets say you have a racket with a 35g head mass and can swing(record it) at 150mph (67.05m/s) and then you get a flashboost with head weight 28g and you can swing that 170mph(75.99m/s)(record this).

Then use vs/vr=(c+1)*mr/(mr+ms) to see what has worked out best for you. (I think c is more 0.7 and a 5g shuttle)

first racket: the 35gram one
Vs/67.05= (0.7+1)*0.035/(0.035 + 0.005)
vs=99.74m/s (223.11mph)

Flashboost one: the 28 gram one
vs/75.99 = (0.7+1)*0.028/(0.028+0.005)
vs = 109.6m/s (245.16mph)

So if you can swing that 28g that faster than the 35g one then hey presto!

11. Originally Posted by craigandy
I think if you want to compare what racket weight is best, you would be best forgetting about using a shuttle, and just record swings speed of only you(personally) seeing how fast you can swing the different weighted rackets, then use line and lengths formula!
No, use the shuttle, and then measure shuttle speed is obviously the most logical thing

12. It's too simplistic a model anyway. Just because you can swing it with a lot of momentum, doesn't mean you'll be good at transferring it to a shuttle.

13. this

says that racket speed of 40m/s *at the tip* is elite badminton player level, so 67m/s - 75m/s is totally unrealistic.

14. Whilst the vast majority of us (myself included) will only ever achieve a string-bed-speed of 20-30m/s, a speed in the region of 67-75m/s was probably needed to set the 421kph record.

Re: wind resistance. I was trying to find a formula to solve: a = -k.v*v, v(0) = V. Maclaurin series diverges too quickly to be useful. Anyone know a good method? If there is one, craigandy could plot several frames after impact and work back to what the contact speed would have been. That said, taking the average speed over the first 2-3 frames after contact will be within a few percent.

Re: momentum transfer to the shuttle. Whilst no contact is instantaneous, this one is short enough for additional force at the handle to make no significant influence what-so-ever. Just watch super slo-mos of balls striking cricket bats or snooker cues. The supposedly rigid timber wobbles like a tuning fork! To get the best shuttle speed for the weight you have, the velocity of the racket head needs to be as square to the shot as possible (no slicing) and as quick as possible at the point of impact.

general approach with short/long time approximation equation:
http://users.df.uba.ar/sgil/physics_...echan/air0.pdf

matlab: in 2d for golfball with drag
http://www.engr.wisc.edu/cmsdocument...ODE-MATLAB.pdf

16. Originally Posted by amleto
No, use the shuttle, and then measure shuttle speed is obviously the most logical thing
No, you can too easily get a bad reading because who knows where on the racket string bed the shuttle came off or if their was slight slice during the test. Maybe a few mm off center makes no difference to feel or sound but big enough difference to speed. I just don't know.

17. Originally Posted by SolsticeOfLight
It's too simplistic a model anyway. Just because you can swing it with a lot of momentum, doesn't mean you'll be good at transferring it to a shuttle.
I think the model formula that line and length came up with is maybe not incredibly accurate for the actual speed of the shuttle but I see no reason why it is not an excellent formula for comparing rackets.

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