Yang Family Tai Chi Discussion Board

DPasek wrote: ChiDragon,

I think that I may finally understand what you are trying to say when you talk about force. I think that you may be mistakenly using FORCE when it would be more accurate to say EFFORT.

In the arm wrestling example, it would be correct to say that you were using less effort than your brother-in-law. It would be incorrect to say that you were using less force, since you both produced equal force.

Your posts would make more sense to me if you substituted “effort” where you say “force.”

As I understand Taijiquan, we train to use the minimal possible effort to produce whatever level of force we are using. But this does not prohibit us from using powerful levels of force.....

DPasek

I agree with you on the part about the less effort but only in push hands. However, arm wrestling is different. If I have to use equal force to get even with the opponent, then I am not using less effort. It is because I have putted myself in a yang-yang position. Where as in push hands, a less effort would be in a yin-yang position.

In my arm wrestling example, I was using less effort is because I was only fajin enough force to counteract the force of the opponent. His 100% full throttle of force is not necessarily my full throttle which agrees with the latter part of your post.


Wu Wei

Newton’s Third Law of Motion states, in general, that for every action, there is an equal and opposite reaction. You absolutely have force equal to your arm wrestling partner. You cannot have less than him. You are using less effort, not less force. You are misunderstanding both “force” and “effort” in your post.

okay.....


Let nature take its course.
Wu Wei

This concept can be confusing, apparently even for physics students, so here is a relevant web site that explains Newton’s Third Law, and can easily be related to Taijiquan:
http://resource-bank.nzip.org.nz/draft- ... ception-2/

Okay!
Arm wrestling is about two hands pushing against each other at the point of contact "O".
Force A ---------------->O<----------------Force B

The forces are straightly muscle strength. It does not rely on a friction force on the table. I am wondering is that equal to two persons pushing against each other while standing on the floor?


In the case of the push-hands:
Force A --------------->O------------------> Froce B

The basic principle is to have the hands of both partners move in the same direction. So, that there is almost zero pressure or zero force at the point of contact. Please note they are not pushing each other and B is trying to move away from A while both hands are stay in contact. My question is does Newton's third law still applies here?


Wu Wei

Newton's Third Law still applies. I realize that it is difficult to understand. I was hoping that the link would help you understand. It applies to push-hands drills with extremely soft contact. It applies to extremely forceful push-hands competitions. It applies to arm wrestling.

Look at the video that was included in the linked article. Whether the pressure is light (the positive and negative lines almost touching on the computer monitor shown behind the two guys pushing each other) or heavier (when the lines diverge), Newton's Law applies.

Quote from your link:

Internal and External Forces. One can carefully use the concept of internal and external forces but this can easily reinforce the misconceptions. We can say that the two forces in the action-reaction pair Green pushing Blue and Blue pushing Green are internal forces if the system is the pair of students. Internal forces cannot accelerate the centre of mass of the system. But students are inclined to think this means the forces cancel.

In the link, Green is pushing Blue and Blue is pushing Green.
In Tai Ji push-hands: A is pushing B but B is not pushing A.

Do you see the difference in both cases?

Chi Dragon,

I am not a physics teacher, so you may be better served by searching the internet for answers to your thinking. Physics is used to understand the reality of nature, even when our minds give us misleading perceptions.

It is my understanding that Newton’s Third law always applies – no exceptions.

If you do not understand something about it, then it is likely that some force somewhere else is not clear (e.g., the foot in the examples given for two people pushing against each other). The force at the point of contact is always equal and opposite when pushing someone else.

The “internal” and “external” example that you quoted is only further confusing you. I think that they are pointing out that if you push your own hands against each other (internal system), you cannot affect your own mass. But when you push against someone else (external system), then their mass can be affected. The use of internal and external forces “can easily reinforce the misconceptions.”

The students pushing each other in the quoted example would be like two children pushing each other in the back seat of a car. They can affect each other, but cannot affect the car (the external system).

I think that you will understand it better if you try to understand it yourself, rather than trying to counter what I have posted in order to try and match your own misunderstandings.

DPasek

I think you understand Newton's third law quite well. However, I think you did not understand the principle of Tai Ji push-hands at all. I was trying to tell you that it is a push-pull situation; but you are kept on telling me it is a push-push situation.

If you understand the principle of Tai Ji, then, you would know that push-push is analogous to yang-yang. And push-pull is yin-yang. If you think both partners are pushing each other, then they are doing it all wrong.

The principle of Tai Ji push-hands:
Wrist against wrist
Force A --------------->O------------------> Froce B

Please note that forces A and B are not pushing against each other but moving in the same direction. Let's say at the point of contact O there is a 1/16 inch gap which means that both wrists are not touching each other. The idea is to keep that distance while both were moving in the same direction at all times. However, in order to ting jin(聽勁), both wrists have to make contact but barely touching each other with no pushing force. I hope I could make this understood. Hence, this is what Tai Ji push-hands is all about.

Jin has magnitude which can be controlled by a long time Tai Ji Practitioner. In other words, the magnitude of jin can be issued(fajin, 發勁) from zero to 100%. At the point of contact, both partners will issue zero jin and listen to whoever fajin first. Zero jin means no force was applied. As soon one issue jin, then the other will feel the amount of strength of the jin by ting jin. However, if both partners are starting to use force to push each other, then there is no need to use the application of ting jin or practice push-hands. Isn't it?

The principle of Tai Ji push-hands is learn not to issue jin, at all times, instead of using brunt force to push against each other by applying Newton's third law. Unfortunately, one will not accomplish the goal of push-hands if one cannot get over this hurdle.

If the two people are touching, then there is force, however minimal, between them. The force between them, as measured at the point of contact, is equal and opposite for the two people regardless if one is trying to move away (“pulling”) and the other is moving towards (“pushing”). The person moving forward (“pushing”) will increase the magnitude of the force at the point of contact if the other’s retreat (“pulling”) does not match the advance. Likewise, the person retreating (“pulling”) will decrease the magnitude of the force at the point of contact if they move away faster than the other person advances. If the advance and the retreat exactly match each other, then the equal and opposite force measured at the point of contact will stay at the same magnitude.

This is why you see changes in magnitude on the graph as the people in the video push each other. But the magnitudes of the positive and negative forces remain equal and opposite at the point of contact (being measured by the two force meters) regardless of whether one person is moving backward and the other person is moving forward.

However, regardless of the magnitude of the force, and regardless of whether one person is advancing and the other is retreating, the force at the point of contact will always be equal and opposite. If both are advancing, the magnitude of the force will increase, but the force measured at the point of contact will remain equal and opposite. If the person advancing has more mass and/or more acceleration (F=ma), then the position of the point of contact will change and the magnitude of the force will increase, but the force measured at the point of contact will remain equal and opposite, as measured at the point of contact, throughout this change.

Equal and opposite means both people experience the same magnitude of force, it does not mean that the magnitude of the force never changes. Equal magnitude of force would mean that the graph would show straight lines without the increases or decreases shown in the video.

Perhaps you are misinterpreting the phrase “equal and opposite?”

How about this: the force that the two people express towards the point of contact will usually be different (e.g., it will not record a straight line when measured with the force meters as used in the video), but the result at the point of contact will be equal and opposite (the amount that the lines on the graph vary from each other will be equal and opposite)?

If the two people are touching, then Newton’s Third Law applies when measuring the force at the point of contact. One person could be unconscious and it would still apply. On person could be on ice or be wearing roller skates and it would still apply. The people could be in outer space, and it would still apply.

ChiDragon wrote:As soon one issue jin, then the other will feel the amount of strength of the jin by ting jin.

Newton’s Law shows that BOTH would feel the amount of strength of the jin equally. If you use the same jin force against an unmoving wall instead of against another person, then you would realize that the issuer experiences the same force returning to them as they are expressing.

It is the same magnitude of force being felt through tingjin for both participants.

Okay....my final question.

What if there is a gap of 1/16 inch between the point of contact. Is there a force there?

ChiDragon wrote:Okay....my final question.

What if there is a gap of 1/16 inch between the point of contact. Is there a force there?

No, unless your body hairs are still touching at that distance, then the force on your hairs would be equal and opposite. The level of force would be equal for you and your opponent to feel with your tingjin.

With the hairs touching, you would likely be using your hair follicle sensors (sensing movements of your hairs) to detect the other person rather than your mechanoreceptors (sensing pressure on the skin), although you could also sense them with your thermoreceptors (detecting heat).

If nothing was touching, then Newton's Law would not apply.

DPasek wrote:If the two people are touching, then there is force, however minimal, between them.

1. The force between them, as measured at the point of contact, is equal and opposite for the two people regardless if one is trying to move away (“pulling”) and the other is moving towards (“pushing”).

2. The person moving forward (“pushing”) will increase the magnitude of the force at the point of contact if the other’s retreat (“pulling”) does not match the advance.

3. Likewise, the person retreating (“pulling”) will decrease the magnitude of the force at the point of contact if they move away faster than the other person advances.

4. If the advance and the retreat exactly match each other, then the equal and opposite force measured at the point of contact will stay at the same magnitude.

T

Okay! Finally, we are going somewhere with this. So, we have four conditions here.
I agree with conditions 1 and 2. However, I only see that conditions 2 and 3 apply in Tai Ji push-hands. That is exactly what was happening in Tai Ji push-hands. Condition 4 is what the practitioners do not want it to occur at any time. Thus it would fall into the category of arm wrestling.