What exactly is a 2nd order differential equation?

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Discussion Overview

The discussion centers around the nature and applications of second order differential equations (DEs), particularly in the context of physics. Participants explore the conceptual understanding of second order DEs, their mathematical formulation, and practical examples in various physical scenarios.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Homework-related

Main Points Raised

  • One participant suggests that a second order DE describes the rate of the rate of change, building on the concept of first order DEs.
  • Another participant notes that classical physics is filled with second order ordinary differential equations (ODEs), citing Newton's second law (F=ma) as an example.
  • Further contributions mention applications in electrical circuits involving inductors, resistors, and capacitors.
  • A request is made for a step-by-step derivation of a second order DE from a real-life application.
  • A specific example is provided involving the motion of a ball thrown upward, leading to the formulation of a second order DE based on gravitational force.

Areas of Agreement / Disagreement

Participants generally agree on the prevalence of second order DEs in classical physics and their applications, but there is no consensus on a specific example or derivation process, as requests for detailed explanations remain unaddressed.

Contextual Notes

Some limitations include the lack of detailed derivations for the proposed applications and the dependence on assumptions such as neglecting air resistance in the ball example.

Who May Find This Useful

This discussion may be useful for students and enthusiasts of physics and mathematics, particularly those interested in the applications of differential equations in real-world scenarios.

Venomily
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A first order DE models the rate of change, e.g. when decay is proportional to time we have the DE: dM/dt = -K.M; this is describing that rate of change mathematically. Am I correct in saying that a 2nd order DE describes the rate of rate of change?

Also, can anyone explain any application of 2nd order DEs to me? I understand it mathematically, but I am interested in how it works in practice like that decay example I pointed out above, hence this post.
 
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Venomily said:
Also, can anyone explain any application of 2nd order DEs to me?
Classical physics is chock full of second order ODEs. F=ma, for example.
 
D H said:
Classical physics is chock full of second order ODEs. F=ma, for example.

Not to mention electrical circuits with an inductor, resistor, and capacitor.
 
D H said:
Classical physics is chock full of second order ODEs. F=ma, for example.

Mark44 said:
Not to mention electrical circuits with an inductor, resistor, and capacitor.

Thanks, but can you go through an example with me? actually point out a real life application (which you guys did) but also deriving a 2nd order DE to model it step by step.
 
If you throw a ball directly upward with initial speed 10 m/s, the basic physics law is "force= mass times acceleration". In this case, the only force (neglecting air resistance) is gravity: -mg. Since acceleration is the second derivative of the position function, taking x to be the height above the ground at time t, we have the differential equation
[tex]m\frac{d^2x}{dt^2}= -mg[/tex]
with initial conditions x(0)= 0, x'(0)= 10.
 

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