# Newton third law

1. Nov 3, 2008

### UNknown 2010

Hello,

True or False:
- According to newton third law, the algebraic sum of the forces in the system is equal to zero.

I think the answer is FALSE because, the third law of newton says that F1 = - F2

and the " - " is for the direction, so that F1 = F2 in the quantity ==> F1 + F2 $$\neq$$ 0

2. Nov 3, 2008

### Jp_Garant

Well, from what i understand from Newton's third law is, any force will have a counter force of the same magnitude in the opposite direction. So, if u add both, it would be zero.. however, i am not sure that is what they are asking..

3. Nov 3, 2008

### Thepoint

If F1 = - F2, the two forces are equal but one is negative
For example,
1+ -1 = 0
At least that is what I think

4. Dec 9, 2008

### redrose_emf

i think its false ,,,
because each force is acting on seperate body,,
so we can not find the the algebraic sum of the forces ,,

:grumpy:

5. Dec 9, 2008

### D H

Staff Emeritus
This question is impossible to answer without further information on what "the system" means. We have a template that specifically asks for 1. The problem statement, all variables and given/known data. You should have followed the template, UNknown.

Sure you can. Just add them vectorially. This is a very important concept. The (vectorial) sum of all internal forces must be zero in an isolated system.

6. Dec 9, 2008

### redrose_emf

thank you for the correction ,,,