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I'd just like to check my understanding of the branches of mechanics. I suspect dynamics is not just concerned with accelerating systems. Doesn't dynamics just generally deal with systems in motion? Those systems can either be accelerating or in dynamic equilibrium (constant velocity), right? Or am I thinking of kinematics?

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  • $\begingroup$ The field of dynamics studies the evolution in time of systems governed by a Hamiltonian, which will include a part describing the interactions in this system. $\endgroup$ Mar 11 '17 at 14:08
  • $\begingroup$ Essentially a duplicate of physics.stackexchange.com/q/1135/2451 $\endgroup$
    – Qmechanic
    Mar 11 '17 at 18:20
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"Dynamics" comes from the Ancient Greek δύναμις which meant power, ability. Dynamics deals with forces, the power behind forces, and their effects on motion.

The basis of dynamics is Newton's second law of motion, which deals with acceleration. Since the initiation of motion and changes in motion always involve acceleration, you generally will find that acceleration is a part of most issues covered by dynamics.

Kinematics deals with motion alone rather than with the forces that cause motion.

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  • $\begingroup$ One question: would it be inaccurate to say that dynamics is the study of systems that undergo acceleration? I thought you could have dynamic equilibrium, in which there is 0 acceleration. Doesn't that fall under dynamics? $\endgroup$
    – AleksandrH
    Mar 11 '17 at 19:09
  • $\begingroup$ @AleksandrH : You're right. Dynamic equilibrium in physics applies when all forces acting on an object in motion prevent that object's motion from changing. There's no net acceleration in dynamic equilibrium. With no net acceleration, there would be no acceleration. But the object's motion still would fall within the study of dynamics. Therefore, it would be inaccurate to limit dynamics to "the study of systems that undergo acceleration". $\endgroup$
    – Ernie
    Mar 11 '17 at 21:05

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