Negative sign in coulomb's law/centripetal motion question

AI Thread Summary
In the discussion about Coulomb's law and centripetal motion, the confusion arises from the negative charge of the electron when calculating the period of its rotation around a proton. The key equations involved are the centripetal force equation and Coulomb's law. When substituting charges into the equations, the negative sign from the electron's charge does not affect the magnitude of the force calculated by Coulomb's law, which only provides the force's magnitude. Therefore, the negative sign is not included when determining the period, as it leads to a misunderstanding of the physical context. Understanding that Coulomb's law focuses on force magnitude clarifies the issue of the negative period.
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Homework Statement


I had a question in my physics class today that was relatively easy but what I was confused about was a misplaced negative sign. "An electron is rotating around a proton at a distance R. The mass of the electron is me and the charge is -e. Find the period."


Homework Equations


Fc=mev2/R
FE=kq1q2/R2
T=2pi*r/v

The Attempt at a Solution


The solution was calculated equating the two equations given above. The problem arises when I plug in -e and +e for the charges. This leaves one side of the equation negative, which results in a negative period. How does the negative sign go away? Do I not include the sign for charges?
 
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No, you do not include the negative sign of charges in Coulomb's Law for the force between two charges. Coulomb's Law gives the magnitude of the force. If you need to know the direction of the force, use the rule that like charges repel and opposites attract.
 
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