Understanding Work: Defining the Price of Electron Redistribution in Electricity

[jbriggs444]

Now put the automobile at rest and the ground has moved 50 meters and the car 0 :)
They skidded on one another a distance d, of course there was some work done on the car and it lost energy, but where did that energy go? Initially to the ground, you'd find that while one lost energy, the other gained it if you keep the axis the same but change point of origin's placement, that is a frame of reference.

The rest frame of the car is not inertial. That complicates the analysis. Can you pick an inertial frame and re-cast the problem using it?

 

[Beanyboy]

What you were told was a direct translation of the formula into English.
Force --- F
is equal to -- =
mass -- m
times -- X (can be omitted; symbols that are adjacent are assumed to be multiplied)
acceleration -- a

When I was an undergrad, I took a year-long engineering physics sequence. The equation F = ma came up so much that my housemate and I decided that if we didn't know this formula, the alternative was "F = your grade."
That's really a backwards perspective. It's the force that causes the object to accelerate.

I don't see how changing the word order in "Force is equal to mass times acceleration" leads to greater understanding.

The formula F = ma is derived from the second of Newton's three laws of motion. See https://en.wikipedia.org/wiki/Newton's_laws_of_motion under "Newton's second law".

That's really got me thinking now. Very interesting indeed. You do know I'm a complete novice here, so feel free to just ignore my ignorance. But, if you're in the mood for explaining ... you're saying "Force causes the object to move". Haven't you altered the expression "Force is equal to mass times acceleration"? Are you altering it for "your convenience"?

So, let me ask you this, are you saying I could/should read the equation as "Force causes mass times acceleration". Looks like I may have some "unlearning" to do! As the great Mark Twain once said: It aint what you know that gets you into trouble. It's what you know for sure, that just aint so."

 

[DarkBabylon]

what was it about your math style that would have pissed off the mathematicians?

Physicists and mathematicians tackle mathematical problems differently. Physicists generally avoid certain mathematical formalism being too obvious or too redundant for certain purposes, or that we like to apply logic and physics to solve a certain equation without needing half a white board worth of formalism, sometimes however we resort to that formalism if we need to. Mathematicians, at least first year undergrads, would be annoyed by just you treating dv/dt as a fraction rather than a derivative, but the annoyance is innocent most of the time.
There probably is nothing wrong mathematically in what I wrote and mathematicians would be fine with it.

Also I do understand that I kinda lost you with the math, but kinda did expect that. However I should point out, the math itself uses algebra and just a tiny amount of calculus. The rest is just physics. All of these are not too complicated to learn, heck sometimes you don't even need the integral and derivatives in certain cases and just solve it with pure algebra. Sure pure algebra wouldn't get you a PhD, but the basic understanding as a layman it is sometimes enough.

 

[Beanyboy]

That's rather ironic, considering the video ends with Feynman exulting the remarkable accomplishment of "Maxwell equations". I also don't see how this has any relevant with the concept of "work" that has been the central question here.

Here's the thing: you can learn about physics superficially by reading pop-science books, watching YouTube video like this, and not wanting to learn about these equations. But you'll never go beyond that level without the mathematics, and understanding the mathematics. There is just no way around this, and Mother Nature has made this non-negotiable.

As I've said a million times, physics doesn't just say "what goes up, must come down". It must also say "when and where it comes down"!

Zz.

I couldn't agree more with you. "Philosophy is written in that great book, which ever lies before our eyes, by which I mean, the Universe. But, we cannot understand it, if we do not first learn the language and grasp the symbols in which it is written. This book is written in the mathematical language... without which one wanders in vain through a dark labyrinth."

 

[Mark44]

That's really got me thinking now. Very interesting indeed. You do know I'm a complete novice here, so feel free to just ignore my ignorance. But, if you're in the mood for explaining ... you're saying "Force causes the object to move". Haven't you altered the expression "Force is equal to mass times acceleration"? Are you altering it for "your convenience"?

No, I'm not altering anything. I was attempting to correct what seems to be a misconception on your part in post #36:

the more you accelerate a massive object, the more force comes with it

The force doesn't "come with it" - the force is what causes the acceleration of the object.

So, let me ask you this, are you saying I could/should read the equation as "Force causes mass times acceleration".

No, read it as "force equals mass times acceleration", exactly like the formula F = ma.

Looks like I may have some "unlearning" to do! As the great Mark Twain once said: It aint what you know that gets you into trouble. It's what you know for sure, that just aint so."

 

[berkeman]

"Force causes mass times acceleration".

No. The force causes the mass to accelerate, and the amount acceleration depends on the values of the force F and the mass m, according to the equation F=ma..

 

[DarkBabylon]

Due to a disagreement with F=ma, let me point out that it is only a derivation and a rule of thumb, not the law itself.
The law itself states that for every body you can assign a quantity of momentum which is equal to its mass times the velocity of the object, which ends up being a vector because of this. Such quantity can be altered, and if we would like to know how much it changes over time we just take the derivative with respect to time. In a sense, we want to know how much momentum does a body get over a certain amount of time. That rate of change, THAT's the force, so in general:
F=dp/dt
Which means now you can talk about a system with a changing mass, such as a rocket.

 

[Beanyboy]

No, I'm not altering anything. I was attempting to correct what seems to be a misconception on your part in post #36:
The force doesn't "come with it" - the force is what causes the acceleration of the object.
No, read it as "force equals mass times acceleration", exactly like the formula F = ma.

12 = 4 times 3. Therefore, if I have 3 repeated, 4 times, then I'd have 12. Here, I've explained the equation without using the word "equals". To my knowledge, I haven't altered the essence, even if I've altered the words. Now it's your turn. Explain F = ma without using the word "equals".

 

[Mark44]

12 = 4 times 3. Therefore, if I have 3 repeated, 4 times, then I'd have 12. Here, I've explained the equation without using the word "equals". To my knowledge, I haven't altered the essence, even if I've altered the words. Now it's your turn. Explain F = ma without using the word "equals".

Why?
The formula uses the symbol '='. My explanation uses the equivalent word in English.
What's your point?

 

[berkeman]

Explain F = ma without using the word "equals".

I just did!

The force causes the mass to accelerate

 

[DarkBabylon]

12 = 4 times 3. Therefore, if I have 3 repeated, 4 times, then I'd have 12. Here, I've explained the equation without using the word "equals". To my knowledge, I haven't altered the essence, even if I've altered the words. Now it's your turn. Explain F = ma without using the word "equals".

It's really hard because we might have an occasion where we have a mass of 3.141592... well pi. Mathematically, you basically repeat the same vector of acceleration yes, but if we just use "equals" it makes the formula general enough to be used for things which are not dependent on neither mass nor acceleration, because now the Force is not strictly limited to those quantities. Physically force can be anything, and it would always also be the rate of change of momentum, or mass times acceleration for unchanging masses.

 

[berkeman]

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