Re: Newton e Hooke

Jonathan Thornburg [remove -color to reply] il 18/02/2025 09:23:09 ha scritto:

In article <vos7hr$gpqq$1@dont-email.me>, Luigi Fortunati writes

In my animation https://www.geogebra.org/m/mrjtyuwk there is the force F of the hand that presses against the car and accelerates it according to Newton's second law (F=ma).
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 [[...]]

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And at point A' *of the hand* does only one force arrive (the blue reaction force of the car) or does the black force F of the hand also arrive?

 
In article <m1g9ofFcmipU1@mid.dfncis.de>, I replied

To answer this we'd have to dig into the the internal structure and
compressability of the hand (which is also an extended body), and where
the musles are that are applying the forces.  The issues involved would
be similar to the ones I just described for forces acting on the car
point A", but I'm not going to go through this in detail.

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I should clarify that part of Luigi's question is readily answered: The
car's reaction force (blue in Luigi's diagram) pushes left on the point
A' of the hand,

I agree with you: the blue reaction force I drew is there and acts on the hand.

and the force of the hand pushing right on the car (black
in Luigi's diagram) does NOT act on (i.e., push on) any part of the hand.
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It's the part of Luigi's question that uses the word "only" that's harder
to answer...

It is not "difficult" to explain that "only", it is impossible.

If "only" the blue force were to act on the hand, the hand should accelerate to the left.

Since the hand does not accelerate to the left, it means that the blue force does not act alone.

Therefore, another force "also" acts on the hand and it is easy to understand which force it is: it is the force of the arm muscles directed to the right, like the black force.

It is due to the action of these two opposing forces (arm and car) that the hand contracts.

It goes without saying that, if the two opposing forces are equal, the hand does not accelerate and if they are different, the hand accelerates.

Ciao.