I What is the Abstract Definition of Energy?

[RonL]

First of all, have you actually observed this happening the way you describe?
If you examined what went on a bit more closely (slo mo camera) you would have seen the impact, in which the bat and the peg were in contact for a finite time. During the contact, there was some distortion of both, which temporarily stored some elastic potential energy. During contact, the batter could also have been pushing against the resistance of the peg. The flywheel would have gradually (over the contact time) accelerated and the bat would have slowed down. Once the contact ended there would be no further acceleration - if you assume the flywheel was rigid. If there were spokes involved the hub could accelerate after the contact time (catching up with the rim and the rim might have accelerated a bit as the peg straightened.
But, once contact had finished, there would be no more energy transferred to the wheel. There can have been no 'magic' store of energy; it must have all been in the strain of deformation of the bat and wheel.

The flywheel gaining speed at impact is what I'm blocked at, if the speed is 100 rpm and at impact the effect is an increase of 10 rpm, so in the space of maybe one degree of rotation the wheel is now slowing from an elevated speed of 110 rpm.
It just has my brain a little twisted, but I'll see it eventually :)

 

[Drakkith]

The flywheel gaining speed at impact is what I'm blocked at, if the speed is 100 rpm and at impact the effect is an increase of 10 rpm, so in the space of maybe one degree of rotation the wheel is now slowing from an elevated speed of 110 rpm.
It just has my brain a little twisted, but I'll see it eventually :)

What's the problem? If you apply a force over some time, there will be an acceleration and the angular velocity will increase. This is just basic mechanics.

 

[nasu]

The flywheel gaining speed at impact is what I'm blocked at, if the speed is 100 rpm and at impact the effect is an increase of 10 rpm, so in the space of maybe one degree of rotation the wheel is now slowing from an elevated speed of 110 rpm.
It just has my brain a little twisted, but I'll see it eventually :)

You really mean "slowing"?

How about a billiard ball being accelerated from 0 to about 10 m/s over a distance of the order of 1 mm, when hit with the cue?
Collisions are usually characterized by large changes in speeds over relatively small distances. And this is because the forces involved during collision are quite large but they act during a short time interval.

 

[sophiecentaur]

The flywheel gaining speed at impact is what I'm blocked at,

OK - not intuitive.
Take it one step at a time. It's easier to think in terms of a linear impact. A railway locomotive traveling at 60km/hour with a thick steel plate on the front, running into a soft squidgy beach ball. You can imagine the contact involving the ball squashing 'till it's almost flat and then bouncing off in front of the train. The impact would last perhaps 0.1s . You have also probably seen pictures and high speed film of golf balls (harder and denser); they go pretty flat during contact. But you don't see that in a game of golf. Now take a steel ball bearing, hit by the train. The steel is very hard and will deform only a small amount until the force is great enough to push the ball away. That process need only take less than 0.1ms but it still happens. In every case, once the collision is over there's no more force acting so no transfer of Energy.
Ones mind has a very narrow range of "what's reasonable". That's why Engineers and Scientists use numbers and measurements.

 

[RonL]

I have seen the golf ball deformation and I am back on track, just not seeing in the correct time frame appears to have been my blunder. I'll go back to what I understand better, a shot of compressed air driving a sliding vane of an air motor, a maximum pressure applied and then energy applied through expansion.
Thanks to each that replied

 

[Mark Harder]

Hi, Abstracted Universes, and welcome to PF!
To me, "energy is the capacity to do work" is actually both intuitive and abstract...

Not quite. Heat is a form of energy, but not all heat can be used to do work. Some just leaks away. In the thermodynamic statement of the 1st law, the change in the internal energy potential of a system is the sum of heat absorbed by the system minus any work done by the system. If a change in internal energy was just the work done, there could be no exchange of heat with the system's environment. But this is true only in special, so-called 'adiabatic', systems. To take one example, there's no other place with which the universe can exchange heat, the universe is an adiabatic system. But creating a practical system that does work on its environment (or vice-versa) yet remains thermally isolated from that environment is a task that can only be approximated, by slowing the exchange of heat to the point where it may be neglected. Thermal energy always plays a role in real-world processes and cannot be simply ignored.

 

[ProfChuck]

Is there a difference between what something does and what something is? Most (if not all) scientific theories, definitions and descriptions are behavioral in nature. In the case of energy we know a lot about what energy does. We know how it can be transformed from one state to another, how it can be stored and released, how it can be focused or diffused and so on. But all of this is behavioral description. Can we truly understand anything in terms of its underlying existential nature? Behavior can be observed and measured and models can be constructed that allow us to predict future outcomes. When these models work can we say we understand the underlying mechanisms or only that we appreciate some of their observable properties?. It seems to me that to ask "what is energy" reveals an attempt to transform behavioral properties into existential identity. I don't think science is equipped to do that.

 

[ZapperZ]

Is there a difference between what something does and what something is? Most (if not all) scientific theories, definitions and descriptions are behavioral in nature. In the case of energy we know a lot about what energy does. We know how it can be transformed from one state to another, how it can be stored and released, how it can be focused or diffused and so on. But all of this is behavioral description. Can we truly understand anything in terms of its underlying existential nature? Behavior can be observed and measured and models can be constructed that allow us to predict future outcomes. When these models work can we say we understand the underlying mechanisms or only that we appreciate some of their observable properties?. It seems to me that to ask "what is energy" reveals an attempt to transform behavioral properties into existential identity. I don't think science is equipped to do that.

It doesn't, and I think most people do not realize that the things that they THINK they know about, such as an apple that I used in my response to the thread that I linked earlier, are also described by a series of its properties and behavior.

So asking for "what is energy?" and wanting an answer that is not a description of its properties is a bit puzzling. It is as if there is another way to answer the question "What is X?" without giving a series of description of the property of X.

It isn't just in Science.

Zz.

 

[Dadface]

If it moves or if it can make things move it has energy.

 

[member 563992]

It is as if there is another way to answer the question "What is X?" without giving a series of description of the property of X.

Oh. That sounds a bit of/like Wittgenstein.

 

[rumborak]

All the above points are certainly true, but I'll also say that it is an interesting thing to at least ponder how these transformations between various manifestations of energy (kinetic, fields etc) are facilitated. Especially when you consider quantum mechanics, where for very short periods of time the energy balance sheet can be unbalanced, i.e. you can borrow energy provided you pay it back in time.

 

[Dale]

Not quite. Heat is a form of energy, but not all heat can be used to do work.

it could all be used as long as your cold reservoir is at absolute 0.

 

[Voltageisntreal]

I got you :D. Energy isn't real as such, that's why you're getting intuitively confused. The real phenomena which we experience would be velocity. That's how we percieve the world, through velocity and mass. Everything can come down to velocity and mass.

The rest is just things we believe in, like energy. You can't measure it because it isn't "real". To measure energy, you have to use it up, at which point it's "forces" at work which we can only REALLY detect because of the velocity they create on massess.

So energy isn't real, hence "real"-ly it's nothing: just a belief we created to help us deal with certain things.

 

[Dale]

And on that note we will close the thread as another great example why these threads are so useless.

The rest is just things we believe in, like energy. You can't measure it because it isn't "real". To measure energy, you have to use it up,

In the future please make sure that your posts do not contain nonsense like this.

 

[fresh_42]

Energy isn't real as such

This is a rather edgy interpretation. There's currently a heat wave here, I'm writing this on an energy consuming device and in my lifetime I more than once accidentally touched a hot wire: Energy IS real.

The point with these kind of questions ["Is <xy> real?" What is <yz> really?"] is, that they cannot be answered without defining a valid framework for an answer first. Such a framework can be found in philosophy or maybe in mathematics. I doubt that it can be found in physics. Physics describes measurable effects, and as energy is measurable as well as has obvious effects, it is real. One can even chose between many forms of energy (see above) and therewith definitions. All of them are real.

So as always with these kind of questions, we have to end the (in my eyes fruitless) discussion at some point and this point has come for this thread, so it will be closed.