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Question

Can higher order derivatives of momentum be useful in creating theories of dynamics if they have conservation principles? Even if they aren't needed, could it be done in theory? For instance, why can't we use tug, the third derivative of momentum, to solve physics problems even though it has a conservation principle? Is it too hard to find tugs in the physical world?

Derivations

Let's define,

$$(1) \quad P_n=\cfrac{d^n p}{dt^n}$$

Where $p$ is momentum. If we take the integral of $(1)$ over a path $C$ parameterized by $r(t)$, and call the result $W_n$, we get,

$$(2) \quad W_n=\int_C P_n(r(t)) \ dr$$

$(2)$ can be simplified a bit to the form,

$$(3) \quad W_n=\int_{t_i}^{t_f} P_n(r(t)) \cdot \dot r(t) \ dt$$ $$\Rightarrow W_n=\int_{t_i}^{t_f} m \cdot \cfrac{d^{n} (\dot r(t))}{dt^{n}} \cdot \dot r(t) \ dt$$

For $n=0,2,4...$ the expressions for $W_n$ simplify to,

$$W_0=\Delta K_0=\int_{t_i}^{t_f} m \cdot (\cdot r(t))^2 \ dt$$ $$W_2=\Delta K_2=\cfrac{1}{2} \cdot m \cdot \dot r(t_f)^2-\cfrac{1}{2} \cdot m \cdot \dot r(t_i)^2$$ $$W_4=\Delta K_4=m \cdot \dot r(t) \cdot \cfrac{d^{2} (\dot r(t))}{dt^{2}}-\cfrac{1}{2} \cdot m \cdot \cfrac{d (\dot r(t))}{dt}$$

The analogy to Kinetic energy should be apparent. In addition, I'd expect an analogy for Potential energy to exist. If we assume these functions exist then,

$$(4) \quad W_n=\Delta K_n=-\Delta P_n$$

Which immediately leads to,

$$\Delta K_n+\Delta P_n=0$$

And then finally,

$$\lambda=K_i+P_i=K_f+P_f$$

However, I am at a loss as how one would actually find real life $P_n$ where $n \gt 1$. For instance, how would deriving the tug of the gravitational field work?

Zach466920
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    The higher order derivatives of momentum are just higher order time derivatives of position. If you know position, you know all orders of time derivative of the momenutm. To know position, using time derivatives up to second-order is sufficient in most of phyiscs, cf. e.g. this question. The higher order things don't contain any information not contained in the lower orders. – ACuriousMind Jan 27 '16 at 01:55
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    @ACuriousMind But it seems like it can be done this way...why hasn't anyone? I mean, I'd be curious to derive some yank fields and draw tug diagrams if it led to something novel. – Zach466920 Jan 27 '16 at 01:57
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    But it cannot lead to something novel. All the information is already there in the lower orders, and generally, calculating with lower-order derivatives is easier. Of course you can use them in some application - but you won't get any new results that one could get in usual Lagrangian or Hamiltonian mechanics. I'm not really sure what you're asking for. Those higher-order derivatives exist, they're just not interesting or relevant. – ACuriousMind Jan 27 '16 at 02:02
  • As primitive as this sounds... science is the description of nature and nature doesn't use higher derivatives. One can, of course, ask why nature doesn't use higher derivatives, which ultimately will lead to the question of causality in physics (forcing second derivatives, I believe) and how classical mechanics derives from quantum field theory. You can, of course, look all day long at the structure of classical mechanics, but you won't learn anything from it... it's not the correct description of the actually fundamental structure of nature, so why waste time on it? – CuriousOne Jan 27 '16 at 02:09
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    @ACuriousMind Well luckily my question is about if it can be done, not if it's useful. Nevertheless, Lagrangian and Hamilitonians are redundant under your argument as they both do the same task this theoretical approach would. So perhaps they'd have use in the right circumstance just like Lagrangian or Hamiltonian. – Zach466920 Jan 27 '16 at 02:10
  • Are you asking if it can be done? Sure... but not in physics. – CuriousOne Jan 27 '16 at 02:11
  • @CuriousOne Physics describes nature, if it can be done in multiple ways all with the same result, who's to say which is physics and which isn't? – Zach466920 Jan 27 '16 at 02:13
  • If I give you nothing but the second derivative of an object's position, you will be able to determine the motion of that object up to a choice of observer inertial system, which leaves physics invariant. If I give you nothing but the third derivative, you will only be able to determine it up to choice of observer system and a constant acceleration term. Unless you think that physics in the ISS and physics on the surface of the Earth are identical, your approach is not equivalent. – CuriousOne Jan 27 '16 at 02:22
  • @CuriousOne Proof? And why do you say the idea would not be physics but then in the next post imply it's used in space? Space has a larger domain of applicability than Earth, so I don't get the objection. Also, using the second derivative, initial jerk can't be determined. Jerk is actually important, people and objects can be damaged if it's too high. In addition, your argument begs the question as to why we don't just use momentum equations and get rid of acceleration. – Zach466920 Jan 27 '16 at 02:28
  • Proof for what? The definition of inertial system? That's Newton's first law. Since you obviously didn't understand the comment, I can only conclude that you haven't quite mastered the phenomenology of classical mechanics, yet, and you can't intuitively distinguish between inertial and non-inertial physics, yet. – CuriousOne Jan 27 '16 at 02:33
  • @CuriousOne Actually I'm referring to your dismissal of third order equations, that part that's not included in CM, and the subjects apparent uselessness on Earth, among other things...It's like you're trying to suggest mass is negligible in space or something. – Zach466920 Jan 27 '16 at 02:39
  • I am simply suggesting that you don't understand Newtonian physics, yet. Look at a few educational videos from the ISS, maybe it will become clearer. – CuriousOne Jan 27 '16 at 02:45
  • @CuriousOne What?...If want me to look something up, you'd be best advised to tell me the subject and the concept I'm missing. Saying I don't understand Newtonian Physics is neither effective nor accurate. I clearly understand large swaths of it, at the least, and if there is something I don't know, it be more efficient to just link or point out my mistake. For instance, you're underestimating the importance of jerk in physics. It has effects on humans. Yet standard mechanics doesn't allow for a choice of jerk in IVPs. – Zach466920 Jan 27 '16 at 02:54

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