Ad-hoc reasoning

[kamil9876]

Some of physics explanations I am unsatisfied with, among them; the law of conservation of energy in certain situations. Let's say an S magnet of mass m is travelling at velocity v towards another S magnet. The velocity of the moving magnet decreases, and hence, so does it's kinetic energy. This loss of kinetic energy we say is converted into 'magnetic potential energy'. Same thing applies to a ball being thrown in the air, loss of kinetic energy=gain in GPE. Now these concepts of 'potential energy' seem quite abstract and ad-hoc in that it's as if they were 'created' in order to satisfy the law of conservation of energy. Therefore it seems that this law is too trivial and not something that actually is of any significane when it comes to predictions and observations. Example: the concept of GPE does not have to be used to work out how long a ball will stay in the air, newton's laws work just fine. In fact, the formula for GPE can be derived from a simple analysis of this situation in terms of newton's laws as well as the definition of work hence it's not a fundamental concept as simple newton's laws are more fundamental and satisfactorily account for the phenomena. So why bother with energy at all?

Now, 400 years of physics can't be flawed like this, hence I am convinced that I missed something and I'm hoping that someone here can fill in this gap in my understanding.

[kamil9876]

A rebuttal to my previous claims:

There was one physics question where the concept of energy was useful and did predict something non-trivial in a non-trivial way.

Let's say some rollercoaster is 10m above the ground, and it travels smoothly down towards ground level and continues travelling horizontally (assume gravity is the only force acting on it). If it was stationary 10m above the ground, and what speed is it moving at ground level (it's moving horizontally btw). Mass of the thing is 10kg.

This can be solved by GPE at top=Kinetic energy at bottom

Something that simple kinematics of the situation can't justify.

Having said that, I still would like replies to this as I'm still just as curious.

[hard]

what are you on about?

[/0]

I *think* kind of have the same problem with energy... sorry if it's something off topic
For example:
Throw a ball up into the air. At the beginning it 'has' (wtf does 'has' even mean) , but gravity does of work on it when it reaches its max height. Therefore, at the top of its trajectory, it should have joules of energy. But! By the Work-Kinetic energy theorem, , which means , so at the top it should have of energy!

[kamil9876]

At the beginning it 'has' (wtf does 'has' even mean)

Yeah, that is relevant to my problem. In a nutshell: I am going on about the need for GPE, it's as though it was introduced just for the sake of conservation of energy being true. Because if we just look at kinetic energy, it looks as if the energy was 'lost', (the thing didnt get hotter nor did it give off a sound) so to *fix* this we introduce GPE, and this is ad-hoc and makes conservation of energy trivially true.

There are other problems, I'll save that for other posts in this thread.

[Mao]

At the beginning it 'has' (wtf does 'has' even mean)

Yeah, that is relevant to my problem. In a nutshell: I am going on about the need for GPE, it's as though it was introduced just for the sake of conservation of energy being true. Because if we just look at kinetic energy, it looks as if the energy was 'lost', (the thing didnt get hotter nor did it give off a sound) so to *fix* this we introduce GPE, and this is ad-hoc and makes conservation of energy trivially true.

There are other problems, I'll save that for other posts in this thread.

I can kind of see where you are coming from, but my understanding of conservation of energy is not 'total energy in a system stays constant', but rather, no energy is created nor lost. In the latter sense, we are saying that energy change in an object is caused by energy transfers (and transformations), and the object cannot intrinsically 'generate' energy (the sun, for example, is merely converting nuclear energy into electromagnetic energy). In that sense, GPE is not really necessary, a falling object's gain in kinetic energy is caused by gravity doing work on it (though I'm not sure if there's a quantized figure on how much gravitational work a mass can do).