Re: defining laws in isolation or 'no other force acting'

David Deutsch <david.deutsch-LR/[email protected]> Mon, 6 Jan 2014 13:41:42 +0000
Newsgroups	gmane.science.physics.fabric-of-reality
Message-ID	<[email protected]>
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On 6 Jan 2014, at 12:23, <hibbsa-/[email protected]> <hibbsa-/[email protected]> wrote:

> ---In [email protected], <david.deutsch@...> wrote:
>=20
>> In that sense, the laws of constructor theory *are* about isolated syste=
ms: the substrate plus constructor.
>=20
> The isolated system doubles as a better way to make clear there aren't ot=
her influences acting. Certainly there are applications where the boundary =
has independent value....say in how the major problems of mechanical engine=
ering were solved (which were fundamental in nature)
>=20
> But, take Newton's laws of motion. Say, an object will remain at rest or =
continue the way its going at constant velocity, WHEN no other forces are a=
cting.=20
>=20
> Does that say that when forces are acting, inertia and the other laws are=
n't also acting? No one would say that. Newton uses forces acting and that =
law in combination to get orbital behaviour, show conservation of momentum =
hence explain elliptical orbit and so on.=20

Newton's first law specifies the behaviour of isolated systems.

Newton's second and third laws specify the behaviour of all systems, isolat=
ed or not. Indeed, the first law follows from the second, if one adopts New=
ton's conception of what it means for a force to 'act'.

-- David Deutsch




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      <p><br>
On 6 Jan 2014, at 12:23, &lt;hibbsa-/[email protected]&gt; &lt;hibbsa-/[email protected]&gt; wrote:<br>
<br>
&gt; ---In [email protected], &lt;david.deutsch@...&gt; wrote:<br>
&gt; <br>
&gt;&gt; In that sense, the laws of constructor theory *are* about isolated systems: the substrate plus constructor.<br>
&gt; <br>
&gt; The isolated system doubles as a better way to make clear there aren&#39;t other influences acting. Certainly there are applications where the boundary has independent value....say in how the major problems of mechanical engineering were solved (which were fundamental in nature)<br>
&gt; <br>
&gt; But, take Newton&#39;s laws of motion. Say, an object will remain at rest or continue the way its going at constant velocity, WHEN no other forces are acting. <br>
&gt; <br>
&gt; Does that say that when forces are acting, inertia and the other laws aren&#39;t also acting? No one would say that. Newton uses forces acting and that law in combination to get orbital behaviour, show conservation of momentum hence explain elliptical orbit and so on. <br>
<br>
Newton&#39;s first law specifies the behaviour of isolated systems.<br>
<br>
Newton&#39;s second and third laws specify the behaviour of all systems, isolated or not. Indeed, the first law follows from the second, if one adopts Newton&#39;s conception of what it means for a force to &#39;act&#39;.<br>
<br>
-- David Deutsch<br>
<br>
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