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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?

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    $\begingroup$ 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. $\endgroup$
    – ACuriousMind
    Commented Jan 27, 2016 at 1:55
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    $\begingroup$ @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. $\endgroup$
    – Zach466920
    Commented Jan 27, 2016 at 1:57
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    $\begingroup$ 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. $\endgroup$
    – ACuriousMind
    Commented Jan 27, 2016 at 2:02
  • $\begingroup$ 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? $\endgroup$
    – CuriousOne
    Commented Jan 27, 2016 at 2:09
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    $\begingroup$ @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. $\endgroup$
    – Zach466920
    Commented Jan 27, 2016 at 2:10

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