S13Phys2BaLec21C

# Although you could try coulombs law for every single

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Although you could try Coulomb’s Law for every single point charge in the floor separately and sum them together for the answer.

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Coulomb’s Law F = k r 2 q 1 q 2 C 2 N·m 2 8.99 9 × 10 [N] [m 2 ] [C][C]
Coulomb’s Law The direction of Coulomb’s Law is determined by the sign of the two charges involved. If you have unlike charges then the force will be attractive along the line connecting the two charges. If you have like charges then the force will be repulsive along the line connecting the two charges.

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Coulomb’s Law To take into account both magnitude and direction, we usually rewrite Coulomb’s Law as: where ε o is the permittivity constant with a value of: ε o = 8.85x10 -12 C 2 /(N m 2 ). ! F elec = 1 4 !" o q 1 q 2 r 2 ˆ r k e = 1 4 !" o Note that the absolute value signs are removed from the charges. If the charges are opposite signs, and hence attractive we get: ! ˆ r + ˆ r If the charges are have the same sign, and hence repulsive we get:
Coulomb’s Law Note the similarities between Coulomb’s Law and Newton’s Law of Universal Gravitation. Both have a proportionality constant. Both depend on the inverse square of the separation distance, r. Both forces “act at a distance,” the objects do not need to be touching. But because k e > G we say that the electric force is a stronger force.

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Coulomb’s Law When performing a Coulomb’s Law problem make sure you: 1) Define a coordinate system. 2) Make a clear diagram of the situation (if one is not given). 3) List the quantities known. 4) Calculate the magnitude from the equation for Coulomb’s Law. 5) Determine the direction (maybe using the fact that “like charges repel, and opposites attract.”) 6) Potentially incorporate force diagrams and Newton’s Laws.
Superposition Calculating the force on one charge due to another charge via Coulomb’s Law is quite simple, the issue becomes when you have multiple charges present.

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