Recent content by fortaq

So, we have to distinguish, on the one hand, between conservative and non-conservative forces, and, on the other hand, between system-internal forces and external forces on the system. I think the problem results from our different approaches to the energy equation: you considered a system...

Why? What happens in that case? I mean, if a system is isolated, then its energy should remain constant, no matter if the forces within the system are conservative or non-conservative.

Yes, we are saying the same thing, but I consider this statement (that the universe's total energy is constant) as the statement with the lowest possible information content about energy conservation. Since the universe is the only system that is actually isolated and any other subsystem may...

This may only be true if we impose constraints on the system, e.g., isolation. But nature itself does not require a system to be isolated so that its total energy is constant, but rather allows energy transfer to or from a system. (Of course, we may always include the energy transferring...

So you mean, merely the ball's potential energy transforms into kinetic energy, therefore no energy is transferred to the ball?

Oh yes, sorry, in my previos post I've asked if the ball's total energy changes or not (and of course it does not), but in fact I wanted to ask if Earth's gravity transfers energy to the ball while gravity performs work (F.dx > 0) on the ball.

But you talk about a system, whereas I talk about a (single) particle that interacts with other particles. That is, dEother does not exist in my equations. But also in the case of a system those other forms of energy (heat, electric, chemical, sound etc.) are in fact kinetic and potential...

Okay, but it is still not so clear for me. Let me rephrase the question: What is energy transfer to or from the particle? a) dK + dU = dE, which is the particle's total energy change. b) dK = -dU + dE, which is the total work performed on the particle. @ PhanthomJay: you seem to prefer...

Hello, The statement in question is: "In Newtonian mechanics, changes in the energy state of a point particle are described by the equation dK + dU = dE, whose terms are the (infinitesimal) changes in kinetic, potential, and total energy, respectively. The total energy change dE describes...

To add to my initial question: Is a conservative system not a system in that all forces are conservative? In that case, namely, answer a) should be true.

In terms of matter and energy. But is a conservative system in fact identical with an isolated one?

Hello, Could someone tell me what a conservative system in classical mechanics is? Is it a) a system in that each particle's total energy is constant OR b) a system whose total energy is constant, but the individual particles' total energies may change. THX, fortaq

Thanks for response. Could you give a reference to a textbook? I thought that Lagrangian and Hamiltonian mechanics are in principle the same and both are variational principles.

Hello! Would you say that the following text is true from beginning to end?: ----------------------- Basically, there are two mechanical approaches to describe a particle: (a) the variational principles (e.g., the Lagrangian and Hamiltonian ones) and (b) the Newtonian approach. The former...