I dont think any shot (forehand backhand slice serve) is hit with the hand/forearm slowing down from the moment when initial acceleration happens to the moment of the contact point. At least not with proper technique.
More physics-based discussion on MgR/I
- Thread starter PistolPete23
- Start date
José Fernando Barba
New User
The forearm never decelerates intentionally, but happens naturally. Force is only applied to start the body rotation, shoulder adduction and shoulder flexion, but since that force is not being kept steady, the different portions of the body start to decelerate. The initial body rotation deceleration increases the aceleration of the arm at the shoulder joint, then the deceleration of the arm acelerates the wrist (and because the swing path is more vertical, the forearm pronates and the shoulder gets into internal rotation, helping both with spin).
tele
Hall of Fame
In the case of the forehand, I think the slowing down of the forearm near the contact point is what causes the racquet to start rotating about the wrist, bringing the racquet around your wrist through contact (i.e. "whip-through"). If the wrist remained in the initial roughly 90-degree lag all the way until contact, it seems like you would have to have your arm perpendicular to the net to make good contact with the ball.
The deceleration of the arm prior to contact is mentioned by Rod Cross and the TW professor on the TWU site and in articles, though the extent of the deceleration in tennis players does not appear to have been extensively studied.
tele
Hall of Fame
Ok, to put it simply in mgr/I terms, you would hypothesize that if two racquets with identical "I" (i.e. "swingweight" about the butt cap) and identical "m" but different "r" were swung at the same initial speed, the racquet with the lower r would rotate faster through contact because it would decelerate the arm (as it "tried" to rotate about its balance point) more before contact?
It’s called recoilweight because it’s a measure of how stable the racket is during the contact – how much it recoils and how much of the recoil shock is transferred to the arm. Higher recoilweight means that the racket is more stable during contact. Low recoil weight is among the most common causes of arm pain and injury.
High recoil weight means that we have to have a lot of mass far away from the balance point, ideally on the opposite poles (tip of the racket and the handle). This is where term polarization comes in to play.
High recoil weight means that we have to have a lot of mass far away from the balance point, ideally on the opposite poles (tip of the racket and the handle). This is where term polarization comes in to play.
tele
Hall of Fame
If you are responding to me, I know what recoil weight is. We have actually been talking about what happens up to the moment contact rather than how the racquet behaves after contacting the ball.
Roads_to_tennis
Rookie
What is this wristband joke? I have also heard tenncom guy talking about wearing rolex... What is all this about
José Fernando Barba
New User
Yes, I was wondering if that could help to decelerate the forearm more and, for that reason also, rotate faster.
At least at the start of the forward swing pulling the racquet handle forward/upwards would make the tip of the racquet go backward/downwards. This rotation happens because the tip goes around the center of mass. The lower the balance, the more you see this effect, and getting the balance higher should decrease the effect, until it could get nullified if the center of mass could be located at 27" (at least hypothetically speaking).
At least I think this contributes in an important way to head rotation in the vertical axis, and was wondering if that same principle could be applied at the end of the forward swing, but this time the racquet head exerting a force over the handle and, hence, decelerating the forearm.
What do you think about that? Maybe the way I'm writing is confusing.
José Fernando Barba
New User
From a physics standpoint, it could increase the "swing weight" of your arm and make the swing slower. For people that tends to start their swing earlier it could be beneficial, since you can always try to compensate if you are late, but if you started earlier it is more complicated.
From a practical standpoint, I also think that is a joke; you would probably need a lot more weight to actually make a difference.
From an economical standpoint.... I would not play better, but would play happier if Rolex were to sponsor me to do that!
tele
Hall of Fame
I think I do at least partially understand what your idea is. The head of the racquet does indeed move backward as the handle moves forward at the beginning of the swing, and if you hold the racquet in front of you and move the handle from side to side with a loose wrist, you can see the head responding in the opposite direction. I am assuming the axis it rotates on somewhere close to the center of mass (which might need to take into account the weight of the hand, as well), so it would make sense that the length of the distance between the tip of the head and balance point would relate to how far the head "recoils" when the wrist pushes the handle forward.
For simplicity's sake, I have been thinking about your example in the horizontal axis so I don't have to worry about gravity. I don't have enough knowledge to give a good answer to your question, but I wonder if a key difference in the two phases of the swing could be the tension the racquet experiences during the part of the swing through contact vs the tension it experiences(or doesn't experience) when the swing is initiated and the head flips around, if that makes sense. I wonder if the tension directed toward the hand when it whips through contact prevents the it from rotating about its balance point, rather than the hand resisting the recoil of the handle (and decelerating as a result) as the racquet head rotates forward, if that makes sense. I really do not know, though.
In addition, if you think of the arm/racquet as a pendulum about the shoulder, the moment of inertia of this pendulum increases as the angle between the wrist and racquet increases, which I think could also contribute to forearm deceleration (and racquet acceleration if the wrist is loose) if the arm is passive at this stage. In that case, I think a higher balance should create a higher "swingweight" about the shoulder than a lower balance would, if m and I remained constant.
laypeople like me trying to think their way through this might be an exercise in futility, but I am always game for discussing/considering other perspectives
José Fernando Barba
New User
Hi everyone! I just finished doing an experiment which turned out to be very interesting. The point was to see if a lower balance resulted in increased racquet head speed, according to the theory I recently proposed.
I purchased an used Head Graphene Touch Instinct S and did a few modifications. I chose that racquet because it has a low static weight (300g strung), low swing weight (295) and a headlight balance (4HL). This is according to TW racquet finder information.
With the purpose of the experiment to show clear differences, I had to make very extreme changes. I decided to do the following:
1. Increase the grip size with 48g of lead from 2cm to 13cm above the buttcap.
2. Wilson cushion aire replacement grip
3. Wilson pro sensation overgrip
4. Added two cotton balls at 10cm above the buttcap to prevent further extension of silicone.
5. 4 bars of hot silicone (4g each) inserted in proximity to the cotton balls
6. 40g of BBs between the buttcap and the silicone.
Considering all that, around 104g were added inside the handle (not really counting the replacement grip and overgrip, since that's normal almost always with any racquet).
That changed the balance to a point around 26.5cm above the buttcap (a 24.5 HL balance if I'm not mistaken).
After that, it was time to try the racquet. The racquet head speed seems to be much much faster than before adding the weight. Doing the same effort to swing it in comparison with a clash 100L that I have (which should be around the same swing weight), the head felt much faster and a much higher pitched sound was heard while swinging the racquet. All that seems extremely subjective, but I don't have an accurate way of making those measurements. I guess I could try to record in slow motion and check how much time it passes between the handle pull at the start of the swing, and the racquet getting to the contact point.
However, where it is less subjective, is that it is impossible to strike the ball with my usual stroke mechanics. If I start the stroke in my usual position, the contact point ends up being at the side of my body, so it feels very awkward. I need to do a very short/almost nonexistent racquet take back to be able to get the racquet to my usual contact point. So, if the racquet makes the same motion in a smaller distance in comparison with a normal racquet, it must be going faster.
This could be explained simply because pulling the handle on a racquet with a lower balance point gets the head down faster because of the lever effect, so the racquet kicks back faster.
I know that a few experiments have shown that increasing the weight in any place decreases racquet head speed, but I don't know if it has been taking into account the stretch shorten cycle that happens with the body, and the fact that a double pendulum model only takes into account movement of the racquet in one axis and not two.
I'll be receiving a briffidi SW1 soon so I can post real measurements.
Any thoughts about this? Have any of you done something similar?
I purchased an used Head Graphene Touch Instinct S and did a few modifications. I chose that racquet because it has a low static weight (300g strung), low swing weight (295) and a headlight balance (4HL). This is according to TW racquet finder information.
With the purpose of the experiment to show clear differences, I had to make very extreme changes. I decided to do the following:
1. Increase the grip size with 48g of lead from 2cm to 13cm above the buttcap.
2. Wilson cushion aire replacement grip
3. Wilson pro sensation overgrip
4. Added two cotton balls at 10cm above the buttcap to prevent further extension of silicone.
5. 4 bars of hot silicone (4g each) inserted in proximity to the cotton balls
6. 40g of BBs between the buttcap and the silicone.
Considering all that, around 104g were added inside the handle (not really counting the replacement grip and overgrip, since that's normal almost always with any racquet).
That changed the balance to a point around 26.5cm above the buttcap (a 24.5 HL balance if I'm not mistaken).
After that, it was time to try the racquet. The racquet head speed seems to be much much faster than before adding the weight. Doing the same effort to swing it in comparison with a clash 100L that I have (which should be around the same swing weight), the head felt much faster and a much higher pitched sound was heard while swinging the racquet. All that seems extremely subjective, but I don't have an accurate way of making those measurements. I guess I could try to record in slow motion and check how much time it passes between the handle pull at the start of the swing, and the racquet getting to the contact point.
However, where it is less subjective, is that it is impossible to strike the ball with my usual stroke mechanics. If I start the stroke in my usual position, the contact point ends up being at the side of my body, so it feels very awkward. I need to do a very short/almost nonexistent racquet take back to be able to get the racquet to my usual contact point. So, if the racquet makes the same motion in a smaller distance in comparison with a normal racquet, it must be going faster.
This could be explained simply because pulling the handle on a racquet with a lower balance point gets the head down faster because of the lever effect, so the racquet kicks back faster.
I know that a few experiments have shown that increasing the weight in any place decreases racquet head speed, but I don't know if it has been taking into account the stretch shorten cycle that happens with the body, and the fact that a double pendulum model only takes into account movement of the racquet in one axis and not two.
I'll be receiving a briffidi SW1 soon so I can post real measurements.
Any thoughts about this? Have any of you done something similar?
Irvin
Talk Tennis Guru
Force (mass times balance) is the force required to rotate a racket around a pivot at the butt cap. But when you grip the racket you don’t apply the force at the butt cap but at some point farther up the racket, I think it’s about 10 cm. When the force is applied farther up the racket any mass below the point where the force is applied counterbalances the mass above the point where the force was applied, requiring less force to rotate the racket. Also mount up 10 cm to apply the force gives you more leverage.
When you applied 48 g from 2 to 13 cm, the mass below 10 cm helps to speed up the racket, and the mass above 10 cm slows the racket down.
bfroxen
Rookie
I just happened across this. The conclusion is correct, but MgR/I describes angular acceleration not the final angular velocity.This one was tricky; I had to think about it for a bit. It would be a good exam question for an engineering physics class
At the moment you run into the wall, the racquet has kinetic energy of (1/2) mv^2, where m is the mass of the racquet and v is the linear velocity you were running at. Even though your body has come to a halt, the racquet is able to rotate freely around your limp wrist, so by conservation of energy, the linear kinetic energy of the racquet must be converted into rotational kinetic energy (RKE).
RKE = (1/2) Iw^2 where I is the moment of inertia and w is the angular velocity.
Since in both scenarios, the kinetic energy of the racquet is the same at the moment of your body's impact, and the I value is the same for both racquets, their respective angular velocities must also be equivalent.
Conclusion: Both racquets, even though having different balance point, will have the same angular velocity.
The numerator (MgR) is a torque. For rotational motion, T=I⍺ (T is torque, I is MoI, and ⍺ is angular acceleration) is the equivalent of the familiar F=ma for linear motion. So, MgR/I is T over I, which is an angular acceleration. You can think of the product of M and R as being the torque that causes angular acceleration, and I is the inertia that resists angular acceleration. So, higher M or R will increase acceleration, and higher I will decrease acceleration. This assumes all else equal, which is often not the case. For example, adding mass at the butt cap will add M but reduce R such that the product of M and R is unchanged.
PistolPete23
Hall of Fame
I haven't been active on this forum and just saw this. What a lot of ppl don't understand is that while MgR is torque, it is torque for rotating motions on the vertical plane, caused by gravitational force acting through the balance point of the racquet. The angular acceleration associated with this torque is MgR/I to rotate the racquet downwards from a horizontal starting point. MgR/I IS NOT a generalized equation for all angular acceleration. For rotating motions on the horizontal plane, MgR isn't relevant.
Big_Dangerous
Talk Tennis Guru
I feel like MgR/I is like George Costanza trying to explain to Derek Jeter and Bernie Williams how to hit home runs in baseball:
bfroxen
Rookie
Sure, MgR is torque due to gravity. Gravity is just a convenient acceleration to use for the purposes of comparison. In the horizontal plane, the acceleration is from a different source, but the ratio of MR/I holds. For a given horizontal linear acceleration (for example, acceleration/deceleration of the hand), a racquet with a higher MgR/I will have higher resulting angular acceleration than one with a lower MgR/I. It's just as relevant for comparison in the horizontal plane.
PistolPete23
Hall of Fame
So on the horizontal plane, all the torque is applied by the player, gravity isn’t contributing. Let’s call this torque, T_app. Then shouldn’t the resulting acceleration in this plane be T_app/I? I don’t see how the balance or static weight would be involved. For a given T_app, the only determining factor of angular acceleration is I.
bfroxen
Rookie
The player can add some torque directly, but that torque is quite a bit smaller than the torque that results from linear force applied by the hand.
First, hold a racquet in your hand with the racquet horizontal and use your off hand to brace your arm so it doesn't move. Rotate the racquet by applying just a torque with your wrist. You can accelerate it, but it won't be very fast.
Second, remove your off hand and whip the racquet through like you're trying to switch position from a forehand to a backhand volley or vice-versa. You can accelerate that rotation must faster. You do that by accelerating and decelerating your hand. The resulting force is at a distance from the center of gravity (balance point), so it creates a torque that rotates the racquet.
You can also think of it like the wall example that @tele used. The wall doesn't apply any torque at all, but it causes a torque because it applies a force at a distance from the center of gravity.
PistolPete23
Hall of Fame
Your reasoning makes perfect sense, thank you. I wasn’t thinking about linear acceleration translating into torque on the horizontal plane in an actual tennis swing. One thing I’d add though is MgR/I shouldn’t be the sole determining factor of how easy it is to achieve rotational acceleration, because you still have to linearly accelerate the racquet as a precursor.
tele
Hall of Fame
thank you for this answer. i am assuming based on the sw1 your physics knowledge is sound, and I had been wondering about this for a long time. I had begun to assume the way I had been thinking about mgr/i the when I posted questions earlier in this thread was incorrect.
anyway, if I may ask one question to make sure I understand, can you say that, in an ideal horizontal swing with a perfectly loose wrist and no air drag, as long as horizontal acceleration and deceleration of the hand were held constant, two racquets with the same mr/i ratios would experience the same angular acceleration about the wrist, even if the m, r, and, i values were differentbetween the two racquets?
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bfroxen
Rookie
A tennis swing is complex, so I'm not able to say much definitive about it. If two racquets have the same MR/I ratio and you accelerate/decelerate the ends of the handles at the same rate, then the angular accelerations of the racquets will be the same. Note that the forces required to cause that angular acceleration may be different. For example, you can add a bunch of mass at the end of the handle, and this will have no effect on the MR/I ratio, but it will require more force to accelerate.
tele
Hall of Fame
that makes eense. thank you！
I see a lot of analysis on MGR/I and stroke mechanics but does anyone have any analysis on correlation between MGR/I and surface speed? I think that could be helpful for rec players because you have some people who only play majority doubles on indoor/quicker courts and some people in who play majority singles on red outdoor clay.
