# S.O.S. Mathematics CyberBoard

Your Resource for mathematics help on the web!
 It is currently Sun, 19 May 2013 02:46:45 UTC

 All times are UTC [ DST ]

 Page 1 of 1 [ 7 posts ]
 Print view Previous topic | Next topic
Author Message
 Post subject: link between Newton’s second law and third lawPosted: Wed, 18 Jan 2012 17:08:50 UTC
 Member of the 'S.O.S. Math' Hall of Fame

Joined: Thu, 16 Sep 2004 10:35:11 UTC
Posts: 545
Could someone explain the link between Newton’s second law and third law

when it comes to finding the resultant force?

Thanks.

Top

 Post subject: Re: link between Newton’s second law and third lawPosted: Wed, 18 Jan 2012 17:35:00 UTC
 Moderator

Joined: Wed, 30 Mar 2005 04:25:14 UTC
Posts: 12074
Location: Austin, TX
kasheee wrote:
Could someone explain the link between Newton’s second law and third law

when it comes to finding the resultant force?

Thanks.

What do you mean? and if you know the initial conditions, that just means the total force sum is the same as the initial forces. (which are usually 0).

_________________
(\ /)
(O.o)
(> <)
This is Bunny. Copy Bunny into your signature to help him on his way to world domination

Top

 Post subject: Re: link between Newton’s second law and third lawPosted: Thu, 19 Jan 2012 00:26:33 UTC
 Member of the 'S.O.S. Math' Hall of Fame

Joined: Thu, 16 Sep 2004 10:35:11 UTC
Posts: 545
Let me give an example so i can better understand.

Lets say I hold pen in my hand and hold it up and keep it stationary. Newton's third law operates. :gravity force = reaction force of my hand

Now lets say I raise my hand. What happens to Newton’s Third law now that we have second law operating?

Top

 Post subject: Re: link between Newton’s second law and third lawPosted: Thu, 19 Jan 2012 02:33:21 UTC
 Moderator

Joined: Wed, 30 Mar 2005 04:25:14 UTC
Posts: 12074
Location: Austin, TX
kasheee wrote:
Let me give an example so i can better understand.

Lets say I hold pen in my hand and hold it up and keep it stationary. Newton's third law operates. :gravity force = reaction force of my hand

Now lets say I raise my hand. What happens to Newton’s Third law now that we have second law operating?

Nothing "happens", as you push up it pushes down more than it did at rest.

_________________
(\ /)
(O.o)
(> <)
This is Bunny. Copy Bunny into your signature to help him on his way to world domination

Top

 Post subject: Re: link between Newton’s second law and third lawPosted: Thu, 19 Jan 2012 05:19:16 UTC
 Moderator

Joined: Mon, 29 Dec 2008 17:49:32 UTC
Posts: 6003
Location: 127.0.0.1, ::1 (avatar courtesy of UDN)
kasheee wrote:
Let me give an example so i can better understand.

Lets say I hold pen in my hand and hold it up and keep it stationary. Newton's third law operates. :gravity force = reaction force of my hand

Now lets say I raise my hand. What happens to Newton’s Third law now that we have second law operating?

No! That is not Newton's third law. Newton's third law says the gravitational forcing pulling down on the pen by the Earth is equal to the gravitational force pulling the Earth up to the pen by the pen. Also, the reaction force of your hand on the pen equal to the reaction force of the pen on your hand. Newton's third law does not assert equality of the the reaction and gravitational forces. For that, look at Newton's first law instead.

_________________

Top

 Post subject: Re: link between Newton’s second law and third lawPosted: Sun, 22 Jan 2012 14:02:04 UTC
 Member of the 'S.O.S. Math' Hall of Fame

Joined: Thu, 16 Sep 2004 10:35:11 UTC
Posts: 545
When you say"the Earth is equal to the gravitational force pulling the Earth up to the pen by the pen", is this equal in magnitude to the "the reaction force of your hand on the pen"? Thanks.

Top

 Post subject: Re: link between Newton’s second law and third lawPosted: Sun, 22 Jan 2012 18:59:56 UTC
 Moderator

Joined: Wed, 30 Mar 2005 04:25:14 UTC
Posts: 12074
Location: Austin, TX
kasheee wrote:
When you say"the Earth is equal to the gravitational force pulling the Earth up to the pen by the pen", is this equal in magnitude to the "the reaction force of your hand on the pen"? Thanks.

How can the Earth be equal to a force pulling it? They're not the same thing, the sentence you wrote is nonsense as-written.

_________________
(\ /)
(O.o)
(> <)
This is Bunny. Copy Bunny into your signature to help him on his way to world domination

Top

 Display posts from previous: All posts1 day7 days2 weeks1 month3 months6 months1 year Sort by AuthorPost timeSubject AscendingDescending
 Page 1 of 1 [ 7 posts ]

 All times are UTC [ DST ]

#### Who is online

Users browsing this forum: No registered users

 You cannot post new topics in this forumYou cannot reply to topics in this forumYou cannot edit your posts in this forumYou cannot delete your posts in this forum

Search for:
 Jump to:  Select a forum ------------------ High School and College Mathematics    Algebra    Geometry and Trigonometry    Calculus    Matrix Algebra    Differential Equations    Probability and Statistics    Proposed Problems Applications    Physics, Chemistry, Engineering, etc.    Computer Science    Math for Business and Economics Advanced Mathematics    Foundations    Algebra and Number Theory    Analysis and Topology    Applied Mathematics    Other Topics in Advanced Mathematics Other Topics    Administrator Announcements    Comments and Suggestions for S.O.S. Math    Posting Math Formulas with LaTeX    Miscellaneous