# Thread: Overall Weight vs Balance

1. Originally Posted by taneepak
Swing speed is fastest with the lightest racquet, but swing speed in badminton is a moot point and in my opinion meaningless. Momentum is everything, and here swing speed has a tiny role.

Momentum though is a product of both the velocity and the mass. Taking the extreme case, you can have a super heavy racquet, but you barely move it, it will not move the shuttle much. On the other end, you have a feather weight racquet moving at a very high speed, the impulse it imparts on the shuttle again will be small.

What we need is to do is maximize not only the mass of the racquet, nor the velocity alone, but the product of the two.

2. Originally Posted by kwun
momentum = mass * velocity
oops, sorry, I'll finish reading the whole thing first next time hahahah...

My excitement about physics took me over by suprise.

oops, sorry, I'll finish reading the whole thing first next time hahahah...

My excitement about physics took me over by suprise.
haha. i like your explanation better.

4. Originally Posted by kwun
momentum = mass * velocity

5. Originally Posted by avaxis
back here again

for the angular momentum you need

Second Moment
It is the infinite sum of all infinitely small mass elements times the square of their distance from the axis of rotation.

* the angular velocity

6. Swingweight is the Second Moment of Inertia. It is possible to have a 4U AT700 with a heavier swingweight, also known as second moment of inertia, than a heavier even-balance 3U racquet. In that case the lighter but heavier swingweight AT700 will generate more power. Swing speed makes no difference, all other things being equal. Of course a Lin Dan can generate more power from a lighter swingweight racquet than you or me with a heavier swingweight racquet-a case of all other things not being equal. Swingweight is not absolute weight but the weight perceived by the player as he swings his racquet. The 4 swingweight factors are weight, head size, racquet length, and balance. For mortals like you and me, these four factors are very real.

7. Originally Posted by avaxis
To answer that, we have to consider not just regular momentum in a straight line that's listed above, but look at the form relevant to us called angular momentum. But since all this talk about momentum isn't getting us anywhere, let me take an energy approach to this answer, which could be easier to understand I hope.

As badminton players we are trying to inject as much energy as possible into the shuttle at the point of impact. That energy comes from the kinetic (i.e. moving) energy available from the swinging racquet. How is this calculated you ask?
--------------------------------------------------------------------
The kinetic energy of a rotating object is proportional to:

1) the length of the swing arm (i.e. longer arm, more energy)
2) the mass of the object (same as what Neil's saying about summing the mass, which you must do since a racquet is not a point object)
3) the square of the rotating velocity (i.e. note the square, I'll come back to this)
---------------------------------------------------------------------

All this means that a head heavy racquet will result in more energy transfer to the shuttle than an even balance, or head light racquet. This is intuitive and we know this well by now. So which type of racquet is best for me, and what's the fastest way for me to get more power, that is the core topic we're exploring here.

Optimal compromise:
Obviously if you can swing a head heavy racquet at very high speeds, you'll be able to facilitate a lot of energy to the shuttle, and you'll be the most feared player at your local club. But what if you can't swing a super heavy racquet. Fear not. Notice that the velocity term in the kinetic energy equation is squared. This means that:

Swing velocity x 2 -> translates into 4 times the kinetic energy.

So if you can't swing a head heavy racquet, no problem! Take a head light or even balance racquet, and the gains you can make by improving your swing technique to produce a faster swing will allow you to make up that lower mass deficit.

Notice here that there are two variables at play in trying to maximize our power. The mass of the racquet, and the swing speed.

What I'm saying is that working on the speed of your swing is the way which you can make the fastest power gain and in the most efficient manner. One could wait until you're strong enough to swing a heavy racquet, but improving the speed you can swing a lighter one in the mean time gives you faster gains in terms of practical power improvement. Comments?

(Note: I didn't want to delve into the difference in angular KE between head heavy and head light racquets right now, which involves talking about how that the center of mass is integrated, and how that is key in the moment of inertia calculation.

The focus of what I'm saying is how can you improve faster: swing faster, or get a heavier racquet?)

8. Originally Posted by taneepak
Swingweight is the Second Moment of Inertia.
Ok please allow me to clarify this then as I can see you guys are waging a war of vocabulary here . The swingweight that you are refering to is from what I can see the length of the racquet times the mass as measured at the center of mass. Also known as the moment of inertia .

What Neil's talking about with the second moment only applies because he's talking about integration of small little finite bits, and the second moment is used when a force is linearly varying over the length of an object.

What you are talking about taneepak I believe is the classic weight at the end of a stick. The whole thing may be light, but most of the mass is at one end. So even though the whole thing feels light, when you swing it, there is a lot of momentum. Am I reading you correctly there?

9. Originally Posted by taneepak
Swing speed makes no difference, all other things being equal.

10. Originally Posted by taneepak
In that case the lighter but heavier swingweight AT700 will generate more power. Swing speed makes no difference, all other things being equal.
*cough*splutter*

11. Originally Posted by Neil Nicholls
*cough*splutter*
hahha...now now.... civilized discourse remember . We must convince taneepak that swing velocity is an integral part of power generation. Along with the mass distribution and the length of the racquet.

12. What I am referring to is that a racquet's swingweight is different depending on where you hold the racquet. If at the butt end the swingweight is highest, if towards the shaft it is lower. It is dependent on the axis of rotation. If I put some counterweight on the handle at a spot close to the axis of rotation of a head-heavy light racquet, the racquet's swingweight has hardly changed, but the second moment is now lower.

13. but you said that a racquet with a greater swingweight generates more power regardless of how fast you swing it

did you mean
at the same angular velocity, the racquet with the greater swingweight will generate more power

[power in the badminton sense of "the shuttle goes faster" rather than the scientific sense of Joules per second]

14. Taneepak, we agree with you that a longer swing arm or a heavier mass distribution at one end of the arm will give more power. What we are debating is when you said the speed of the swing makes no difference.

Again, let me take an extreme example. Two racquets, one is even balance, another is head heavy. You are saying that speed makes no difference. So I can pick up the even balance racquet, swing it, and send the shuttle off at speed x. But I'll just hold the head heavy at 0 velocity, let the shuttle bounce off it. By your argument, the shuttle should have been returned at the same speed x. I'm sure we agree that a non moving racquet will not be able to impart much energy on the shuttle, regardless of where you hold the handle.

The argument about mass distribution and swing arm length is only the static portion of the physics here. There is an equally important dynamic portion which is in play. A 2 ton truck travelling at 50kph will do a lot less damage if rammed straight into a wall, than a 500 ton mining truck at the same speed. At the same time, a small meteor of say 1ton, travelling at > 10000 km/s will do way more damage than that mining truck. The difference is in the kinetic energy each has. That depends on BOTH the mass, AND the velocity. If the speed didn't matter, then the meteor would have just bounced off the earth, and the dinosaur's would be in my back yard.

15. Lets use a badminton example. Power strokes require a back swing to have some leverage. A thunderous smash requires much more back swing than a lightning brush stroke at the net to kill a net shot. The huge back swing of the smash stores energy and the momentum for the powerful smash. Let us assume you use a 2U La Fleche Ti 500 for this powerful smash. You now swap your racquet for a \$10 racquet, restring it with the same string and tension as the LF Ti500, and then repeat the smash. Same back swing, same hand speed or swing speed, do you think you can repeat the power of your previuos smash? The difference is in the different behaviour in the swing weight of the racquet during the smash. The swing weight of the two during dynamic play is worlds apart.
Back to the brush stroke at the net. This requires a hand speed even faster than the smash, but its power or shuttle speed is no where near as fast as from the smash because it has almost no back swing or energy buildup.
Now do you think the power of a smash comes more from the efficient use of the huge back swing or just your hand speed with a limited back swing? Wouldn't swing weight during dynamic play be more important to a player than his swing speed? Are you sure the hand speed of power players is faster than those top players who are less endowed? Isn't the efficient use of the back swing, in all its various permutations, the defining difference? For a player swing weight can make a significant difference.

16. Originally Posted by taneepak
......
Back to the brush stroke at the net. This requires a hand speed even faster than the smash, but its power or shuttle speed is no where near as fast as from the smash because it has almost no back swing or energy buildup.......
It's not true actually that the racquet head speed is faster for net play. The racquet head speed is much slower than when you smash. The acceleration is what is fast, but due to the short time it is allowed to act (quick stroke), the velocity hasn't reached a high value.

Two different things here. The racquet head velocity is not faster than a smash for the net shot you described. Only the acceleration is.

17. taneepak, i am lost in your use of the term "swing weight". what is your definition of swing weight? i assume you meant momentum (mass * velocity) or angular moment (Force * distance) or is it something else? without a precise definition, i have problem comprehensing your argument.

It's not true actually that the racquet head speed is faster for net play. The racquet head speed is much slower than when you smash. The acceleration is what is fast, but due to the short time it is allowed to act (quick stroke), the velocity hasn't reached a high value.

Two different things here. The racquet head velocity is not faster than a smash for the net shot you described. Only the acceleration is.
604badder is correct. in a net brush, the acceleration is high, but i am not sure if the acceleration is higher than the smash at the initial stage. but what is true is that both speed (distance/second) and momemtum (mass * velocity) and thus stored kinetic energy (1/2 * mass * velocity^2) of the racket head in a brush stroke is much lower than the smash.

on top of that, the brush net stroke hits the shuttle in a cut/brush motion, much of the energy is coverted to rotational energy of the shuttle.

all these factors together results in a much lower resultant velocity on the shuttle after a brush net shot.

19. Swing weight, in layman's term, is "dynamic weight" or how it feels when you're wielding or using the racket, i.e. in the arc of a badminton stroke.

Like a moving car "weighs differently" than a stationary car. Don't know if this helps.

The scientific formula for it removes understanding, ha-ha ...

The definition and discussion took place in this thread.

-dave

20. Just trying to make a side observation about this ongoing discussion. I can see that a reason our messages don't seem to be getting through to each other is because of the way we are using specific words. Terms like the weight of an object, and the mass mean two completely different things to an engineer. Momentum is a very specific measure, and it can't exist without something traveling at speed. Speed is different from velocity, the second implies a direction while speed is just a scalar number.

To get things back on track, I think we need to settle on a common vocabulary. I've seen this problem before when I saw computer scientists mingle with their MIS counter parts in commerce. Words were the same, meanings were drastically different.

And just what are we discussing anymore here guys Are we trying to establish what type of balance is best for someone? I've now lost track.

21. ## Balance point has nothing to do with Head-Heaviness???

A strange thing is noted today during my search for the 'ideal' racquet.

I have had a bad time with AT800 OF - I blame it for being too head-heavy.

I was able to try one AT500 from a friend and amazingly I didn't feel any head-heaviness at all! It feels really good! So I was talking to myself yeah this one should be an even-balanced one although all technical details I could find about AT500 said it was also a head-heavy racquet.

I was confused so I tried out the good old method of balacing the two racquets on my index finger in parellel, man it confused me even more when I saw that the AT500 and the AT800, were having almost-the-same balance point! (the distance from the bottom of handle to the balance point is about the same!)

So - my limited physics knowlege tells me that a head-heavy racquet should have a balance point closer to the head of the racquet, and an even-balanced one should have a balance point closer to the bottom of the racquet - am I right?

22. Let's say we have a symmetric dumb bell and a uniform rod of the same length and mass. They have the same balance point (the center).

But the mass of the dumb bell is concentrated at the ends, whereas the mass of the rod is spread uniformly throughout its length.

If you hold each object at one end and try to swing it, you will find the dumb bell more sluggish, because it has a larger moment of inertia.

This is an extreme example, of course, but I hope it makes the physics involved clear.

23. Indeed-- "head heaviness" doesn't imply necessarily a higher balance point, but rather more concentrated weight at the head, as opposed to possibly equal, though more spread out weight, in the handle. Search for "swing weight" on the forums, and you should be able to find topics mentioning it. Swing weight I find is more relevant than so called "even-balanced" or "head heavy" or whatever ratings that Yonex gives, they're notorious for not being able to label things consistently.

Swing weight is generally more apparent when you actually swing the racket, for the reasons Cheongsa expplained, as opposed to balancing it; someone could probably give you a better physics lesson on it, but the head weight concentration's further distance from the fulcrum of motion multiplies it's apparent weight. On a more even-balanced racket, the head's weight is more spread out, and thus it's concentration is less far from the fulcrum, and thus, you get less of an apparent weight multiplier.

24. The beam of the AT800OF frame is a larger boxed shape compared to the AT500's frame beam, to give it a higher swingweight and hence power. The AT800OF also has a stiffer flex than the AT500. It needs more strength to use the AT800OF than the AT500.

25. Originally Posted by Neil Nicholls

...

so you can see that 2 racquets with the same weight and the same static balance point can feel different when you swing them if their weight is distributed differently along the length of the racquet.
Good one! - solved my problem! Thanks.

The weight distribution along the racquet MATTERS!

Wonder wether Yonex put some mysterious extra-heavy material right in the tip of the Armortec 800 racquets

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