## anonymous 3 years ago Newton's third law with magnetic forces? Now while I was studying more about this matter, as I asked before when two bar magnets attract do they both their forces on each other? The answer was "YES." Now, let me go indepth with this more and more, when two bar magnets of un-equal forces attract! Do they equally apply the same force or no? Imagine Magnet A capable of applying 50N of force while magnet B is applying 10N of force, they both attract! I think the two forces add up! What do you all think?

1. anonymous

Although I studied this more and found the following statement: "Another demonstration might be to show two bar magnets. Choose one that is stronger than the other; demonstrate this by showing that one can lift a greater iron weight than the other. Ask: If the two magnets attract one another, will one pull more strongly than the other? The answer is, no. You can feel that they pull each other equally. (This is because the force is proportional to the strength of each.) If magnet A pulled magnet B more strongly than B pulled A, you could attach B to the front of your car and lean out, holding A in front. Your car would move effortlessly!" I doubt this case is true... How is it possibile for a unequal forces of unequal strength apply an equal force of attraction on each other?!

2. anonymous

3. anonymous

@Mashy

4. anonymous

5. anonymous

@ghazi @Hero

6. anonymous

I'd generally think that both force will be added up to attract each other. Its not like on magnet is in charge of attraction, but both of them are. Not sure though...

7. anonymous

Yea, for some reason I feel this statement "You can feel that they pull each other equally. (This is because the force is proportional to the strength of each.)" Is wrong... They pull on each other equally... Maybe that means they BOTH apply their forces on each other? Thus they both add up? I highly doubt that they attract each other equally since one is stronger than the other.

8. anonymous

They attract each other equally.. doesn't matter which magnet is stronger and which one is weaker... you need to understand how force fields work.. the force that a magnet puts on something not only depends on the magnet.. but also on that something else.. Take gravity for example the force put by earth on moon = force put by moon on earth.. Earth produces a stronger gravitational FIELD.. and moon produces a weaker one.. similarly in electric charges.. and magnetism is no exception either..

9. anonymous

ow, I need to study this all over again. good luck @OneOwOne.

10. anonymous

@Mashy So having a weak or a strong magnet attracting another magnet makes no difference?

11. anonymous

Tell me the difference in this case where on magnet has 40N of pull force and the other has 20N. Case 1 40N and 20N. Case 2 20N and 20N. What factors would be different? @Mashy I don't understand how there is no difference since they equally attract... There has to be a catch here.

12. anonymous

I'd say the more the force they greater the attraction. Case 1 has a stronger attraction force than of case 2. Does that makes sense?

13. anonymous

Newtons third law reigns. forces between two interacting bodies whether coulomb, magnetic, or gravitational when one pulls or pushes on the other so the other reacts is kind.

14. anonymous

point 1... "Tell me the difference in this case where on magnet has 40N of pull force and the other has 20N." .. makes no sense.. thats what you need to understand .. the difference between contact forces and field forces.. .. would it make sense i said Earth has 10000N of pull force??? no right?

15. anonymous

how much pull force does earth have??? it pulls you with 600 N force maybe (considering you wegh 60kg :D).. pulls me down with 720 N force... so the FORCE depends on what it is pulling or pushing.. !!

16. anonymous

Ok, when two magnets attract. THE FORCE that attracts a magnet is a contact force or a force field force?

17. anonymous

Im just asking you all when two magnets attract, we know that they BOTH apply a force on each other, for me to calculate the net force should I add them up @Mashy

18. anonymous

@Mashy Or to make this even more simple describe this statement: "They attract each other equally..." In depth explanation needed!

19. anonymous

QUote: "Tell me the difference in this case where on magnet has 40N of pull force and the other has 20N. Case 1 40N and 20N. Case 2 20N and 20N." This statement is simply irrelevant/nonsense. There is no such thing as the "pull force" belonging to A magnet. The force is an interaction between TWO magnets, not a property owned individually by one magnet or the other. You are mistaking field created by a body and resulting force of that field on another body. Your misunderstanding has nothing to do with magnets, but it is more profound and has to do with the meaning of "force", "interaction" and "field".

20. anonymous

A).. we are talking about field forces here.. field force due to an object depends on i think 3 things a) the quantity of the property that creates the field (for example in gravity how much mass, or for magnetism and electricity.. how much charge) b) how far away you are from the object these two uniquely determine the strength of the field at any point.. for example.. the strength of the magnetic field due to any magnet at any particular distance from it is always a constant.. but how much force it exerts on the something else.. depends on that something else too hence for the force.. one more factor comes in c) the target object.. now i am going to use this formula for the force between any two poles of a bar magnet $F = \mu q1 q2/4\pi r ^{2}$ where q1 and q2 are magnetude of magnetic poles in amp - meter look at the expression.. what you see?? the force of attraction or repulsion always depends on BOTH the poles that are in the picture.. thats always true.. for any sort of field force you take.. for contact force its obvious that two forces are equal.. this should make you understand that even for field forces.. the two forces are always always always EQUAL..

21. anonymous

I understand why you are having this problem... thats because you are trying to think of this force on the similar lines of the normal contact force that we are so familiar with.. for example i can say i can exert a push force of exactly 200N .. that makes perfect sense regardless of who the target is.. but field forces are something totally different.. you need to read about it more.. i say start with gravity.. cause thats where it all began.. did you know even though Sir Issac Newton realized that planets revolved cause sun was exerting a pull force on them... he just couldn't convince himself how that was possible .. at that time. the very concept of "force at a distance" seemed so preposterous.. but today we take it for granted.. I advice you to read about FIELDS.. m sure there will a good tutorial on what fields are .. please go through them.. they will definitely explain the concepts of fields way better than m doing :D.. and sadly m a physics teacher :P..

22. anonymous

@Mashy Could you explain to me, why is it when I bring a magnet and another stronger magnet with greater "mass", I feel a STRONGER force of attraction or repulsion, than using two magnets of the same mass + strength? What is the reason for the force being stronger? could you relate what you've said to this situation? With the inclusion of contact force? Thank you! I'm still reviewing what you've said.

23. anonymous

If you bring a heavier magnet then it means the pole strength is stronger.. and hence you see the q values in the above equations become stronger and thus the force of attraction is stronger.. and are you saying that.. if there is one magnet which is smaller than the other then force of attraction is higher.. then you are wrong. you may only feel like that cause, in that case the smaller magnet accelerates faster ( F=ma) and you may "feel" that bigger acceleration hence the force maybe be bigger.. but if you took two big magnets even of same size rest assure you would get bigger force of attraction!.. the relative size difference plays no role what so ever!

24. anonymous

@Mashy I must clarify a few things here... Newtons third law still applies! I agree, and just now realized its not relevant to what I was trying to say! The statement is true about Newton's 3rd law. Now about the larger magnet with greater mass... LOL, its a known fact with more mass comes more strength to the poles. One magnet can be 20Grams and the other can be 5Grams, True the 5g magnet will accelerate more not only because of its low mass, but also because there is more applied force of attraction in this setup, then if there were 5g magnet attracting another 5 g magnet. Thanks for your efforts! I appreciate it!

25. anonymous

I just didn't understand the statement properly... xD

26. anonymous

which statement mate? .. so you still have doubts huh? :D.. m not so proud as a teacher now :P

27. anonymous

No no I don't have any doubts. It just Newton's 3rd law applies. But I just didn't understand how?! Now I knew and it's completely not related to what I was thinking about!

28. anonymous

But I got to ask! When two magnets attract is the force added up? Does that make any sense? Since I know now both of them apply a force. What is the best way to calculate force of attraction! Never found a suitable formula that works in all cases.

29. anonymous

complicated stuff! Really...

30. anonymous

no forces don't get added up.. you just have one force that acts on both of them in equal amounts but in opposite directions

31. anonymous

Ok, how can you calculate that "one force".

32. anonymous

this one force of attraction of repulsion is interesting!

33. anonymous

by the formula i just mentioned :D .. but thats for bar magnets with negligible sizes..

34. anonymous

For some reason I though when two bar magnets attract they BOTH apply a force of attraction, but that force of attraction is just one force applied on both magnet right? The same is applied with repulsion?

35. anonymous

thought*

36. anonymous

YES they both apply a force on each other (attraction or repulsion).. but both those forces are always same in magnitude and opposite in direction.. what i mean't is forces don't get added up.. .. :P

37. anonymous

Um. Now this is really confusing...

38. anonymous

Why is it that they are always of the same magnitude? When they apply their forces?

39. anonymous

cause the force that they apply depends on WHO is applying the force and ON WHOM is the force is being applied! both factor comes into play

40. anonymous

I am telling you.. thats how force fields work!!.. you need to study more!! study the basics of it!!

41. anonymous

Indeed I will. Thanks Mashy for enduring the whole time. Just one last thing: this statement: "If you bring a heavier magnet then it means the pole strength is stronger.. and hence you see the q values in the above equations become stronger and thus the force of attraction is stronger.." Contradicts this one: "they both apply a force on each other (attraction or repulsion).. but both those forces are always same in magnitude and opposite in direction.. what i mean't is forces don't get added up.. .. :P" I'll start studying this all over again, any recommendation where to start?

42. anonymous

no no.. i mean't when you take two different cases .. like two different pair of magnets! and compared heir forces

43. anonymous

So if you take to different magnets and compared their forces... "they both apply a force on each other (attraction or repulsion).. but both those forces are always same in magnitude and opposite in direction.." ?!

44. anonymous

To avoid all this confusion... I'll simplify my understanding, To magnets of the same mass, type, strength attracting each other is not equal to two magnets on greater in mass + strength but of the same type. What is the difference? Both acceleration and force! They are "GREATER". Assuming that the larger magnets is fixed, and in the previous set up on the magnets is fixed too. Each magnet applies a force on one another. And Newton's 3rd law! Still applies. If we think about it, we have two magnets applying force on each other that will equal 2 forces, and both of them are getting the equal opposite reaction force and that will total to 4 forces... And that is true because, take a motor for example, it uses an electromagnet and a permanent magnet, the electromagnet is te coil, and the permanent magnet is the armature. As the coil feeds more electric power, its field becomes stronger and thus the armature is repelled/attracted with a higher force. @Mashy My final sum up!

45. anonymous

I confused my self with kinds of forces and their reactions in certain system, as you and I know, forces are quite complicated. But knowing the basics is quite enough :)

46. anonymous

NOO.. only 2 forces :-/.. not 4 forces.. one magnet applies a force on the other.. and the other applies a force on the first.. thats all

47. anonymous

The 4 force includes those two force, AND Newton's 3rd law! The equal and opposite force GENERATED by those two orignal force = 4. @Mashy

48. anonymous

NOooo.. the two forces are action reaction pairs mate!!!.. they themselves form the action reaction.. !!

49. anonymous

Ok. Apart from the 4 force is my summary good enough?

50. anonymous

The 4 forces part is a mistake. So everything else is good?

51. anonymous

especially the (Both acceleration and force! They are "GREATER".) part.

52. anonymous

ermm yea yea :)!

53. anonymous

loool Thank you.

54. anonymous

this was a great ONeowONe session :P

55. anonymous

lol :P

56. anonymous

I've done this experiment a few times and proved myself right. I taken two different mass and pole strength and two similar masses and poles strengths and noticed te major difference. Greater mass magnet vs small mass + pole strength = significant force + acceleration in comparison to two same sized + strengthen magnets.

57. anonymous

@Mashy I'm just trying to find the best formula to represent the attraction/repulsion force.

58. anonymous

nooo not this again :D.. please try to understand magnetic force depends on what it is putting force on if you have three magnets A B and C it doesnt make sense to ask how much force does magnet A put? rather you talk about how much forces A and B put on each other or how much A and C put on each other!!

59. anonymous

@Mashy I don't know how I didn't mean that... Again, two magnets apply the force of attraction/repulsion on each other not only one magnet. I know that. B applies a force to A and vice versa and A applies a force on C and C does the same to A. Now what I was trying to say... The rate of that force depends on many factors. One of them is pole strength that you and I agree on... If A's pole strenght is stronger than B A applies a stronger force, that does not mean B is doing nothing... Its doing the same but with a weaker force compared to A. And that is what I've proved to myself to be true throughout the experiment. @Mashy what lead you to think this way? In my last statement or the one before?

60. anonymous

why can't you try and think in terms of gravity?.. earth and moon.. ?? even thought we say earth has MORE gravity.. what we really mean is it has a greater gravitational field.. or acceleration.. and moon has less.. but the force they put is the same.. on each other!

61. anonymous

Sorry @Mashy but why did you agree with this statement: "To avoid all this confusion... I'll simplify my understanding, To magnets of the same mass, type, strength attracting each other is not equal to two magnets on greater in mass + strength but of the same type. What is the difference? Both acceleration and force! They are "GREATER". Assuming that the larger magnets is fixed, and in the previous set up on the magnets is fixed too. Each magnet applies a force on one another. And Newton's 3rd law! Still applies. If we think about it, we have two magnets applying force on each other that will equal 2 forces, and both of them are getting the equal opposite reaction force and that will total to 4 forces... And that is true because, take a motor for example, it uses an electromagnet and a permanent magnet, the electromagnet is te coil, and the permanent magnet is the armature. As the coil feeds more electric power, its field becomes stronger and thus the armature is repelled/attracted with a higher force." The only thing I can find wrong is the "and both of them are getting the equal opposite reaction force and that will total to 4 forces..." Sorry that is totally wrong. Aside from that you said this was fine. Tell me are these setups equal? Magnet A(1) = 20g ceramic magnet Magnet B(1) = 80G ceramic magnet A(1) ARE BOTH ATTRACTED A(1) ----> Setup 1 B(1) AND A(1) ARE BOTH ATTRACTED ----> Setup2 Now let me explain, and maybe you can correct me yeah? No, they are not equal. Setup 2 has B(1) and that magnet has more mass = higher pole strength.The force applied in Setup 1 is less than the force applied in setup two. @Mashy I know we have been on this for a while sorry, but its important to me, please hang in there! Could you answer using what I've said make me understand a whole better.

62. anonymous

Even if I used the formula that is based of the two part magnets F=μq1q2/4πr2 I notice that the number of "q" is greater in setup2 = higher total force. And that Q is dependent on the mass of the magnet.

63. anonymous

And I'm not talking about newton's third law just generally what happens between two magnets.

64. anonymous

Even when you look at an electric motor and increased current, you basically increase the electromagnet's pole strength thus the total F is higher.

65. anonymous

"but the force they put is the same.. on each other!" This statement is killing me! :P Why are they equal? Can you prove that using my two examples? Setup's 1 and 2 and the electromagnet? Thanks @Mashy Sorry for putting you in this annoying place but hey! Your helping out a lot.

66. anonymous

And your own statement @Mashy supports my point: "If you bring a heavier magnet then it means the pole strength is stronger.. and hence you see the q values in the above equations become stronger and thus the force of attraction is stronger.." When you say a heavier magnet= More mass= greater pole strength = Force of attraction will be stronger/higher/greater BECAUSE of that "heavier magnet". The force of attraction is due to both magnets, however, the rate of those forces being strong/weak depends. In my cause its strong because one of the magnets is heavier in mass and stronger in the poles. And when I tired this, I FELT THE FORCE. Not acceleration because I held two magnets between my fingers and compared, acceleration was = 0. So I felt the force of attraction.

67. anonymous

@gleem @Vincent-Lyon.Fr

68. anonymous

I still do ont understand what you are doing. It seems it's going on and on. As @Mashy and me have said before and at length, Newton's third law of motion is CONFIRMED by the laws of magnetic attraction. Concentrate on understanding it. You are wasting your time trying to invent cases where this would not be true.

69. anonymous

@Vincent-Lyon.Fr I believe there is a major confusion here... MAJOR! Makes sense why you and @Mashy did not understand me. PLEASE PLEASE PLEASE forget the point of NEWTON'S THIRD LAW.

70. anonymous

To avoid this major confusion I'll write down a new question and mention you all there.

71. anonymous

lol :D..

72. anonymous

Lets begin again. One thing that was left uncorrected in the previous discussion is that the pole strength is related to the mass of the magnet it is not... A light magnet can be much stronger than a heavy one. A term which should be eliminated from this discussion is "rate of force" It means nothing to me and I am sure to many others. OK? You say you have done some experiments with magnet but from reading above you did not use instruments to measure forces but used the feel of the force to gauge its strength which is very subjective. A light strong magnet is indistinguishable from a heavy weak magnet. in fact you cannot determine which one is stronger from their interaction. You can determine which one is stronger using a third magnet to interact with each separately. Do you see that? To demonstrate the force between the two magnets is the same strength consider the diagram with two different strength and size magnets separated by a rigid non magnetic wall with two identical springs between the wall and each magnet. |dw:1360941913137:dw| . You would find that the compressed length of each spring is the same demonstrating the force on each magnet is the same. The force on A due to B is equal to the force on B due to A. I'll stop here and see what you think.

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