### Re: Repel force of a magnet

Date: Sat Jan 1 19:44:36 2005
Posted By: Keith Jones, Secondary School Teacher, Physics, Rhyl High School
Area of science: Physics
ID: 1104451632.Ph
Message:

((Moderator's message: This may be a homework problem, but I can't be sure. You may wish to give a way to learn about how to solve it rather than give a direct answer.))

Now we need to know a little bit about Newton's 3rd Law of Motion (You may know that Sir Isaac Newton was a very famous scientist who lived between 1643 and 1721, and he set out 3 laws which help to explain how and why objects moved).
His third law explains what happens when two objects are pushing or pulling each other - this is what your two magnets would be doing if they were close to each other.
So if object (magnet) A pushes/pulls on object (magnet) B with a force of X (usually measured in Newtons, but you can use "lbs", although it's not very good Physics) then B will also push/pull on A with the same force X. So for magnet A that would be 50 lbs.
But of course magnet B is also pushing at magnet A with its own repelling force, so magnet A will also push back at magnet B with this extra force. Now then, how do you think you calculate the total repelling force between the two magnets?
For extra information about Newton's 3rd Law you can look at http://www .physicsclassroom.com/Class/newtlaws/U2L4a.html

Hope this helps.