# Thread: Physics questions on badminton

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I hope the simple home shuttle throwing test suggested earlier will be an eye-opener to a better understanding of a shuttlecock's spin.

However, to help avoid any more misleading 'expert' opinions in the future may I point out the following untrue claims:

1. "The way the feathers are over-lapping with a clock-wise spin (travelling from you) of the shuttle will mean it will travel faster.........."

This is wrong. All current feather shuttlecocks have their feathers overlapped in the same direction and they will all spin counterclockwise, not 'clock-wise' (travelling from you).

2. "Never heard of a spinning shuttle will travel faster and go further".

The proof can be found in your simple home shuttle throw test to debunk this.

3. "Smashing with a slicing action (in generating more spin) the forward velocity will decrease".

Smashing with a slicing action is a 'moderated' smash with less power and speed but it reduces the spin or rotation rate, not increasing it. The slicing action does not in any way create any additional spin. In fact it 'moderates' the spin rate which means a reduced spin rate.

4. "A smash done with a spinning of the feather will be slower and will have less power".

All shots, smashes, clears, drives, drops will generate spin. The slower the spin the easier it is for the human eye to discern, the faster the spin the more difficult to observe. It is this detectable spin that fools 'experts' into believing they have added more spin to say a sliced smash. This is not true.
Again, the more powerful the smash the faster the spin rate.

2. ## Physics explained

After reading quite a few 'expert' opinions which are by nature contradictory, I thought I'd give some definite points which can be used too further fuel this wonderful discussion. There has been a lot of speculation on this board on the effect of spin (whether it is counterproductive or not and by how much?). There is a paper available online from the ISB Journal of Physics on 'Deceleration of a Shuttlecock' wherein they have explained the concept quite minutely and have given a valid formula that one can use in the calculation. You can find it here-- http://www.isb.ac.th/HS/JoP/vol4iss2...1Badminton.pdf

Admittedly, there isn't much information regarding the effects of 'more' spin in the research but one can at least get a fair idea of the physics of the decelerating shuttle in a normal circumstance. In fact there is always some spin when the shuttle leaves the racket after its hit (One can see any of the numerous slow motion videos posted by Yonex marketing dept. to see that).

Let the discussions continue...

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jeez im getting a headache here
i think i must leave this forum as im afraid i read so much bs on topics im unsure about and read so much wrong stuff

here is your answer, its very simple:

more spin on a smash = less speed q.e.d.
that is because the feathers widen more the more they do spin and therefore have more air-resistance which makes the shuttle slower

all comparisons with other sports are ridicolous as the badminton shuttlecock is such a unique sport item

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Hmm, Not sure if I agree with all of the explanations given.

There's a few fundamentals that need to be realised.

1. There are two processes which impart spin on the shuttle. Spin imparted by the racquet & spin imparted by the airflow due to drag over the feathers.

2. Propellers add forward thrust as they "bite/screw" into the air due to their shape. Shuttle cocks do not have this shape & cannot impart forward thrust.

3. The spin on a shuttle will always settle on the path of least resistance (i.e. least drag)

So. . .
The faster you hit it the more natural spin will be on the shuttle due to drag over the arranged feathers. The natural spin is dictated by the speed not the other way round.

If you hit the shuttle with more/less spin than the natural for that particular speed you add more drag. If you cut the shuttle to take away spin the air resistance will speed up the rotation. If you cut the shuttle to add more spin air resistance will slow the rotation.

Rather than thinking of a propeler on a plane think of a sail boat.
If the wind is 10 mph & your drifting at 5 mph raising your sails will speed you up.
If your travelling at 20mph on the engine then switch it off & stick your sails up the sails will act like a airbrake & slow you down to 10mph.

tanepeeks pretty much got it on the money apart from making the distinction between the two ways that spin is put on the shuttle. In his example's he's only really talking about spin from air drag.

Using his example You should notive this effect:
If you try & throw a shuttle with lots of spin it will slow down it's rotation.
If you try & throw a shuttle with no spin it will speed up it's rotation.

Any change in spin speed is due to drag. Any energy required to slow/speed up the spin is sacrificed from forward speed.
Last edited by mindfields; 04-23-2012 at 10:12 AM.

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## Pakito's Theory of Relativity on Shuttle Spin

Hey guys, I am no scientist, and frankly all this quantum physics has made me all 'corkscrew'y in the data processing machine seated in my skull.

Let me chip in on my theory of the spin. As of now, one says that the spin slows down the shuttle, the other vice versa.

While it is true (I feel) that the shuttle does spin on its own irregardless of whether it is sliced or not, I feel that the spin is indeed really a 2 faced coin.

Spinning is in fact aroused and heightened by both speed and slice. But the fact for me is this: ever notice that the shuttle starts out fast and speedy on alot of spin, then it's like those Dragsters' sports where the dragster fires out a parachute and severely slows the speed of the dragster? Well, this is what happens in theory of the spin. And to cement this theory, virtually all fast spins (spins due to tremendous input power and slice from the racket) are all shots that land at the frontal area of the court, never the baseline. This is because its starts out fast by input of strength of hit by the player, and then sliced at the same time. The high input of kinetic force forces the shuttle to spin faster, boosted by the slicing motion of the racket on the shuttle (think snooker), and for the first part of the shuttle flight trajectory, it travels fast indeed, fooling the player to stand closer to the baseline. Almost in a quick milliseconds later, the shuttle suddenly lands nearer to the frontal area of the court. This where majority of the shots are used to fool their opponents. This effect cannot be achieved (at least in my theory) for lobs, lifts because palyers don't sliced them for a full perfect high lift. You can sliced a jab or a push a little, but not a lift, because the lift will fall low and fall short. This is why intense shuttle spinning (revolutions per second) happens a lot on downward trajectory shots ie the smash, half-smash, sliced fast drop (there is a distinction between a slow falling drop and a sliced fast drop).

So why fast at the beginning and slowing down at the end? Because the spin is a mechanism that needs slicing and kinetic force to start up, but once it's started up, spin speed increases till it comes to a break point when the feathers open up (think of a peacock) and causing more resistance and thereby, intense speed reduction.

Don't get me wrong, a shuttle does spin even with a full smash down the line without a slice, but compared to the smash coupled with a slice, the straigh smash spins slower.

PS: Shuttle spin (rotary motion) and shuttle tumbling motion (horizontally and vertically orientation) are both different aspects of defination of the motions defined.

Why I say this theory is a 2 faced coin?

Speed and sliced ---> increased the spin of the shuttle ----> increasing spin creates a vacuum in front of shuttle head (think of turbo engine) ------> shuttle speed increases even more -------> shuttle spins reached a criticial level where the feathers has to opens due to outward spinning momentum of the feathers ------> feathers opening outward increases friction on flight trajectory (think parachute) ------> as speed decreases so does the spinning (this is why commentators can see the spin when is slow, but not on initial flight straight from the racket because its too fast for the eye to define) ----->shuttle falls short of its intended length and drops in front of the opponent. Opponent is tricked.
Last edited by Pakito; 07-23-2012 at 01:14 AM.

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So much theory about spin and still getting confused.
Here is from a shuttlecock manufacturer's brief explanation. When we make shuttlecocks we have to test all shuttlecocks for rotational speed (spin) and stability on a special machine. This machine is different to another machine that tests shuttlecock's speed and distance. An average non-nylon shuttlecock has a rotational speed or spin of about 320 revolutions/minute, plus/minus 5 revs/m, with an average stability. A higher grade could be as high as 480 revs/m, plus/minus 5 revs/m, with very high stability.
The higher quality shuttlecock can spin/rotate faster and still maintain very high stability at such high rotational spin because of its higher quality feathers and shafts. Obviously, winter goose feathers are the best.
The faster a shuttle is hit the faster the spin/rotational spin, limited by the shuttle's spin limit. A duck feather shuttlecock has no hope of reaching a 480 revs/m and will travel at a spin of 320 revs/m when hit with power, which will collapse the feathers inwards a bit because the shafts are not strong enough, resulting in having higher wear and tear and loss of speed over a relatively short period of time.
The bottom line , insofar as shuttle manufacturing is concerned, is that the best shuttle must have very high rotational speed with very high stability when hit with power.
Now, you don't want to buy shuttlecocks with slow spin/rotational spin when hit with power.
Stroke techniques such as slices and so called "net spins" affect the shuttle's rotational spin by slowing it down in both speed and its natural rotational spin. In other words, the faster a shuttle's rotational spin the faster and the more stable the shots.
What happens is subject to 2 forces, gravity(pulling down) and air resistance (pushing up), that will affect its motion.

7. So, are the manufacturers saying that centrifugal force or the corresponding coriolis effect does not come into the picture, with relevance to the direction/path/vector of the bird? If a bird spins/rotates on any axis along any path, I would think that centrifugal force (no matter how weak or how insignificant or how strong or significant) would come in to play, unless I've got my funadmental physics all messed up.

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Yes, it is as pakito said, the more force impacted on the shuttle the faster it travels (with natural spins). The faster it travels (faster spins), and the higher the resistance. It is like the law of diminishing returns as the natural spin produces drag.
The slope of the graph will get less steep when u increase the force. After the shuttle leaves the racket, it is slowing down as resistance push the shuttle in opposite direction.

Now the slice. When we artificially slice the shuttle (putting a smaller vector on forward direction and some torque to create the spin), the increased spin does not increase the speed, or it does not add to the forward direction vector. In fact the spin will increase the resistance to the forward motion.

Think of it as projectile, and the vectors involved. The spins in the natural flight is the just the natural shape and feather position - the design.
If you "crashed" the feathers inward, less resistant (do u know some prayers actually trained to break the bird when smashing?) . If the feathers "puffed" outward due to slice or natural phenon (both due to speed), more resistant is generate to the projectile.

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When you slice a shuttle or execute a tumbling "spinning" net shot, you are actually slowing down the shuttle's rotational spin speed. A "spinning" tumbling net shot can be likened to a dis functional "spin" shot, exactly like a fast spinning top that has been given a sideways knock so it loses its rotational spin and begins to "wobble". Wobble is sometimes wrongly mistaken for spin, which it is not. A shuttle wit a broken or missing feather will visibly wobble, which is actually a loss of stability for that spin rate, thus resulting in the wobble.

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Originally Posted by chris-ccc
.
You have reminded me of this:

The current plastic shuttlecock will travel faster than a 'feathered shuttlecock' in a smash because of these reasons;

* Without spin, the plastic shuttlecock (compared to the feathered shuttlecock) will travel faster in a smash.
* With less rigidity of the plastic 'skirt' (compared to the stiff feather shaft), the plastic skirt collapses (folding inwards).

Therefore, a smash with a plastic shuttlecock is usually faster and/or more powerful than a smash with a 'feathered shuttlecock'.

Maybe, this is another topic... And perhaps, we can start another thread on this one.
.
Good old juggernaut has closed the case and hammered in the nail on this example! Case close.
Oops, sorry I have no power to close the case. I'm not the moderator.

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