1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

B Why does an attractive force always have a negative sign?

  1. Jul 25, 2016 #1
    I've seen in many equations of physics that whenever we demonstrate an attraction force we tend to use a negative sign before it,why is that? In case of coulomb force it makes sense because when the charged particles are of opposite signs a negative sign is sure to be appeared.But why do we necessarily use it for gravitational force?Well,I know that we use the negative sign for gravitational force for vector representation only.That's all right,but I want to know whenever we use a work done by an attraction force we use a negative sign,viz: the gravitational potential.It is written in books that the gravitational potential is negative because the work to bring an object from infinity to the gravitational field is done by the gravitational force itself,no external force is provided.But what's the relation between the gravitational force's doing the work and the sign's becoming negative?
    Shafia.
     
  2. jcsd
  3. Jul 25, 2016 #2

    Dale

    Staff: Mentor

    In the usual radial coordinate system the positive r direction is outward. So a repulsive force is in the positive r direction and an attractive force is in the negative r direction .
     
  4. Jan 4, 2017 #3
    Think of it like this Positive(P) x Negative(N) always gives you a Negative(N), whereas when you times PxP or NxN It always equals to P. you can apply this to Charged Particles Two postives give a Repulsive force ( P) and two non-alike charges give a Negative, therefore you can say that attraction is negative.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Why does an attractive force always have a negative sign?
Loading...