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Acceleration

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Original Message Post # 1
Wed 7th May 2008 13:16
user18082

USA-4-1030
Joined: 04/12/2006
Topics: 6 Replies: 18
I have a bit of a technical question for anybody who can give me any kind of answer?
 
If I have a technique, lets say a punch moving at a steady pace of 40 mph from its start point to its finish point.
 
And I have another technique
 
Lets say the same punch starting at 10 mph and accelerating to 40 mph.
 
Which technique has more power, and why?
 
 
Respectfully
 
 
John Szostek
Post # 2
Top Wed 7th May 2008 14:15
Michael Boik
Joined: 15/04/2007
Topics: 11 Replies: 35
I hate Math!!! With all else equel, I would say both have the same power since both are traveling at 40 MPH at the end. Now, if you have different Mass, say a bicycle and a train both traveling at 40 MPH, the train would have more Power. Dead
Taekwon!!

Mike

www.drysdaletkd.com

Post # 3
Top Wed 7th May 2008 17:48
Francois Bertrand

CAN-5-1010
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The answer is quite simple. The scientific equation for force is F=MA or Force equals mass X acceleration. Also speed and mass are two important elements of the theory of power. Basically, the more you have of them the greater the force will be. However, one doesn't go without the other. As it is explained in the TKD encyclopedia where it compares the impact of a large stone gently dropped on a pane of glass from a height of three inches versus a small stone thrown against a glass with great speed, you will see that the outcome is greater with the small stone as the weight increases with speed.

Furthermore, the speed of any technique will gradually increase when performed as you would be starting from a "fixed'" state (fist was not moving before you started to execute the punch) therefore one cannot have a steady pace.

François Bertrand

V Dan, Demers Taekwon-Do School

Canada

Post # 4
Top Wed 7th May 2008 19:22
user18082

USA-4-1030
Joined: 04/12/2006
Topics: 6 Replies: 18
Mr. Bertrand

Sir have you ever seen a students who's movements seem robotic? Because the acceleration is lacking. There technique hits there maximum speed before the end of there movement, then rides out at that speed till the end. This makes the technique look robotic. I just was wondering if there was a difference in power, or it was just the same?


Respectfully


John Szostek
Post # 5
Top Wed 7th May 2008 23:34
Francois Bertrand

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Mr Szostek,

I think I know what you meant as robotic movements, but still my interpretation may be different from yours. In my interpretation of a robotic movement, I notice that movements are not fluid but more sequential. That being said, the sine wave and the execution of the movement along with other elements might not be performed appropriately. In that case, one can assume that a student would have less power when he execute the technique.

Furthermore, you clearly identified the concern in your reply "Because the acceleration is lacking". If we apply again the scientific equation for force (F=MA) or Force equals mass X acceleration, then the power would be less if the accelaration is lacking.

Taekwon

François Bertrand

V Dan, Demers Taekwon-Do School

Canada

Post # 6
Top Thu 8th May 2008 02:10
Nick Malefyt

USA-6-1015
Joined: 04/12/2006
Topics: 2 Replies: 50
Doc,

Along these same lines I might tell you to take a look and see if the attacking tool is rotating at the right point:

Punch - twisting at the end
Thrusting = less twisting
Striking = least twist

Many times while punching students rotate their fists to early (more like a push compared to a punch) - and the speed stays constant - compared to speeding up and rotating at the end

Just a thought!

Nick
Post # 7
Top Mon 12th May 2008 15:29
user18082

USA-4-1030
Joined: 04/12/2006
Topics: 6 Replies: 18
Getting back to the Acceleration point.

The technique would be traveling at a fixed speed / velocity and not accelerating. So the formula Force =M x Acceleration or V squared would not work. thus the technique would not be as powerful.

Respectfully


John Szostek
Post # 8
Top Thu 3rd Jul 2008 19:44

Joined: 02/11/2010
Topics: 1 Replies: 8
Just a thought, In a straight punch, would the reaction hand come into play, would it increase speed and power if performed correctly?
Mr. Brennan
Post # 9
Top Fri 4th Jul 2008 00:27
Adam Gibbs

GBR-4-1154
Joined: 22/09/2007
Topics: 1 Replies: 4
Sirs, In my humble opinion...

As we all know, force is equal to the mass of the moving object(s) multiplied by the speed of motion at the point of impact. eg

If a car travelling at 30mph hits a wall the equation is force = weight of car X 30mph.

If the driver applied the brakes and slowed the car to 15 mph at the point of impact the equation reads force = weight of car X 15mph. this is less than A.

I have been playing with reaction hand speed and find that if, on a punch the reaction hand is retracted with as much energy as the punch is delivered, the force of the punch is much greater, I put this down to the rotation of the upper core and shoulder area being greater, therefore adding mass to the technique. The punch travels at the same speed but the mass is amplified as the two extra areas are now also moving, all be it in rotation as opposed to linear.
When I perform this in what I believe to be a correct fashion the fist connects with the target with out the throwing of the shoulder. IE front punch is full facing on contact of technique, (although it does pass through the target when breaking). Somthing else that changes is the timing of the punch in a self defence situation, although I believe this is easily addressed if practiced.

If it helps: the amount of force of my reaction hand on punching is approximatly equivalent to that of a rear elbow strike.

This rings true with the phrase ' an equal and opposite reaction force' (Theory of power) which I remembered after coming to my conclusion.

Taekwon
Post # 10
Top Tue 8th Jul 2008 18:34
David Sims
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Joined: 30/05/2007
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Sir,

I was under the impression that force = mass X acceleration

and power = mass X velocity2 (velocityXvelocity) (velocity here means travelling in a straight line)

however the definition for force and power are dif
Post # 11
Top Sat 12th Jul 2008 23:16
Adam Gibbs

GBR-4-1154
Joined: 22/09/2007
Topics: 1 Replies: 4
Thank you sir.

And can I say wow at the eye opener I have had this week in tracking down the variations to this question, and have a great amount of reading.

As you correctly point out, Newton’s 2nd law does in fact point to force = mass X acceleration and this is the way that Gen.Choi explained it in his writings, and correctly so.
I hope that what I put here then now is justifies what I previously wrote.

When an object has an applied force it will accelerate, if it was accelerating to an undetermined velocity and at the moment of impact it was travelling at 40mph it would certainly carry more power than a fist travelling at a constant velocity of 40 mph (That’s the answer to the beginning of this string).

When a punch is thrown it does have an equal force against it at the end of its range of travel that force is, I believe this to be tensile force, that of the arm and shoulder being fully extended and the joints being at their full range of movement. If the arm carried a velocity onward and upward of 40mph the 2nd law would be totally applicable. But realistically a punch will stop accelerating at some point, our training shows us to accelerate past the point of impact - but the punch will still stop even so. This is why I believe that Newton’s 3 laws should all be used in TKD at the same time for each technique.

With this in mind it brought me onto our kicks, is side piercing kick more powerful than a flying side kick at the same velocity?

Is there a scientific research area for the ITF to get the definitive answers to these very technical questions? The physics of which are way beyond me. Wouldn’t it be great to tweak moves for the absolute optimal output under the eye of the ITF and have this documented for all?
Post # 12
Top Mon 8th Nov 2010 16:52
MikeCarr

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The F=MA equation is commonly mis-used.

Consider the fist at the point of impact, do not consider it anywhere else. If the final speed of the fist is 40mph, any accelerations that happen before the point of impact will not effect the momentum of the fist (speed x mass).. This momentum will be transferred to the target, and the target will be forced to accelerate towards 40mph, it is this forced acceleration that causes damage to the target or the fist. The acceleration will cease once the speed of the fist and the target are equal... However this 'terminal velocity' will be less than 40mph unless an acceleration of the fist is initiated immediately after the point of impact.

The fist will decelerate upon the point of impact due to the transfer of energy (lets say the deceleration is 60m/s^2) - this means that 0.5 seconds after the point of impact the fist is now travelling at 10mph.. In order to balance this out, AT THE POINT OF IMPACT the fist needs to accelerate by 60m/s^2 for one second... In other words, to make the fist travel the same speed before and after the point of impact, it must accelerate immediately at the point of impact.In other words, to make the fist travel the same speed before and after the point of impact, it must accelerate immediately at the point of impact.

So difficult to put into words lol
Post # 13
Top Sun 15th Jul 2012 11:07
Bosse W
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The equation F=MA is a pretty bad equation and as MikeCarr states misunderstood in several aspects. From purely physics point of view one should understand that the F is the resulting force of all forces acting upon an object. In the present form people with high school physics knowledge tend to think of this as a pure scalar translation rather than a vectorized equation. The resulting force gives the mass M an acceleration A. Going into the details of the physics when hitting a human body is pretty complicated, what is interesting is the amount of energy transfered to the object/body and this is dependent upon the time energy is transfered during the impact and the way the material/body bahaves/moves. The initial value for the speed is of interest just before the contact. The energy transfer upon impact is entirely dependent upon the material characteristics of the body, most people probably have a gut feeling for the difference in energy transfer between hitting a feather and a brick wall. When hitting a brick wall most of the energy is transfered into the wall while when hitting a feather most energy is lost as heat in the muscles when you have to stop the arm yourself. To go into details one should rather look at solid mechanics rather than "pure physics" and this is not easy. Thus, the conclusion, you don't come very long when reasoning in terms of simple Newton mechanics F=MA and Wk=MV^2/2. t it general describes elementary movements but it can't explain much when it comes to the impact on a real human body.
Post # 14
Top Sun 22nd Jul 2012 17:58
JBCAlaska

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Greetings - I too have heard confusion in both class discussions and in threads specific to this topic, but believe that the take home message is that an increase in your speed of a punch or kick, will significantly enhance your 'capacity to perform destruction' (trying to stay away from the use of words like, force, power, energy). The specific 'energy' that your attacking tool has when it is moving is in the form of kinetic energy that includes mass and velocity (KE = 1/2 * m * v * v), and you are gonig to want to transfer it elsewhere (and hopefully not back on your own hand when attempting board breaking). Since your velocity is in that equation twice, this means that you get bigger bang for your buck with a slight increase in your speed (it is multiplied twice, or squared in the equation). Since mass is also part of that equation, we should also work on increasing the mass relative mass of the attacking tool (not by eating mind you) by incorporating core rotation, which provides effectively puts more of your personal mass behind the attacking tool. I also believe (as stated above) that the reaction force we invoke (in many, but not all instances) also helps counter the maintenance of the attacking tool 'mass' by helping to keep our momentum in a forward direction to the attack. Reaction force is not always applicable in real fight situations, but speed and rotational mass certainly are...hope I didn't add to the confusion!

Best regards -
John Carnahan - ITFUSITF -- Alaska, USA
Post # 15
Top Mon 23rd Jul 2012 20:45
MikeCarr

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Here's an interesting text you can try at home which might help you think outside the whole force/power issue.. Take a housebrick and place it on the ground (supported by two other bricks at each end) as if you were going to break it with a stamping kick or downward punch ... Put on some shoes and stamp on it as hard as you can - If it's a decent strength brick it probably won't break .. Now take a solid stone and grip it in the palm of your hand, give the brick a firm tap in the centre and it will probably break clean in half.

The point of this experiment - Although stamping on something as hard as you can probably has a lot more energy/power than tapping something with a stone.. Because the stone is so hard, it transfers all that potential energy/power straight into the target.. Sharpen up your tools and you're already streets ahead
Post # 16
Top Fri 27th Jul 2012 12:35
Bosse W
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Quote from JBCAlaska - 22nd Jul 2012 17:58 View
Greetings - I too have heard confusion in both class discussions and in threads specific to this topic, but believe that the take home message is that an increase in your speed of a punch or kick, will significantly enhance your 'capacity to perform destruction' (trying to stay away from the use of words like, force, power, energy).

Best regards -


I agree totally.

Post # 17
Top Fri 27th Jul 2012 12:38
Bosse W
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Quote from MikeCarr - 23rd Jul 2012 20:45 View
Here's an interesting text you can try at home which might help you think outside the whole force/power issue.. Take a housebrick and place it on the ground (supported by two other bricks at each end) as if you were going to break it with a stamping kick or downward punch ... Put on some shoes and stamp on it as hard as you can - If it's a decent strength brick it probably won't break .. Now take a solid stone and grip it in the palm of your hand, give the brick a firm tap in the centre and it will probably break clean in half.

The point of this experiment - Although stamping on something as hard as you can probably has a lot more energy/power than tapping something with a stone.. Because the stone is so hard, it transfers all that potential energy/power straight into the target.. Sharpen up your tools and you're already streets ahead


A good example where the importance of material charateristics for the energy transfer is quite obvious and the "Theory of Power" isn't explaining very much.

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