Balancing Electric and Gravitational Forces Between Two Objects

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Homework Help Overview

The discussion revolves around balancing electric and gravitational forces between two small objects of equal mass (3.0g) by transferring electrons. The original poster seeks to determine how many electrons need to be transferred for the electric force to equal the gravitational force.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants explore the relationship between gravitational and electric forces, attempting to set the equations equal to each other. There are questions about the implications of transferring electrons and the resulting charges on the objects. Some participants express uncertainty about the relationships between the charges and the forces involved.

Discussion Status

The discussion is ongoing, with participants providing guidance on expressing relationships between the charges and exploring the implications of charge conservation. There is a focus on clarifying the net charge of the system after electron transfer and how that relates to the forces in question.

Contextual Notes

Participants are working under the assumption that the objects are initially neutral and are discussing the implications of charge transfer on the forces acting between them. There is a recognition of the need to express the net charge in terms of the individual charges involved.

DubbzWubbz
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Homework Statement


Two small objects of equal mass 3.0g are placed a certain distance apart. How many electrons must be transferred from one to the other so that the electric force between them is equal to the gravitational force between them?

Homework Equations


Coulomb's Law: F = K (|q1||q2|)/r^2
Gravitational Force: F= GMm/r^2

The Attempt at a Solution



Well I assumed I was looking for a proportion between gravitational force and electric force which would allow me to decide the electrons necessary...so I attempted to set the two equations equal to each other, however, I really don't know what to do with this information or if it is even right. Could I get some advice on how to start appropriately.
 
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DubbzWubbz said:

Homework Statement


Two small objects of equal mass 3.0g are placed a certain distance apart. How many electrons must be transferred from one to the other so that the electric force between them is equal to the gravitational force between them?

Homework Equations


Coulomb's Law: F = K (|q1||q2|)/r^2
Gravitational Force: F= GMm/r^2

The Attempt at a Solution



Well I assumed I was looking for a proportion between gravitational force and electric force which would allow me to decide the electrons necessary...so I attempted to set the two equations equal to each other, however, I really don't know what to do with this information or if it is even right. Could I get some advice on how to start appropriately.
You shouldn't let doubt and lack of self-confidence overwhelm you so early in doing your work.

Since you know the forces due to gravitational attraction and electrostatic charge are supposed to balance, how would you write that relationship in terms of the two laws governing these phenomena?
 
(GMm)/k = |q1||q2| ?
 
DubbzWubbz said:
(GMm)/k = |q1||q2| ?
Yes. Assuming the objects are initially neutral, what is the relationship between q1 and q2?
 
DubbzWubbz said:
(GMm)/k = |q1||q2| ?
Read the problem How many electrons must be transferred from one to the other...
 
haruspex said:
Yes. Assuming the objects are initially neutral, what is the relationship between q1 and q2?
The product of the two charges are proportional to the force?
 
DubbzWubbz said:
The product of the two charges are proportional to the force?
No, that's a relationship between the charges and the force, that you already found. I'm asking about a relationship just between the two charges. Read the question statement, and assume the two bodies are initially neutral.
 
haruspex said:
No, that's a relationship between the charges and the force, that you already found. I'm asking about a relationship just between the two charges. Read the question statement, and assume the two bodies are initially neutral.
If both q1 and q2 are neutral, there would be no attraction? I assume I am transferring electrons to create a charge.

(GMm)/kq2 = |q1| q1 is proportionate to GMm/k multiplied by 1/q2. Would q2 be the charge of an electron?
 
DubbzWubbz said:
If both q1 and q2 are neutral, there would be no attraction? I assume I am transferring electrons to create a charge.
Initially neutral, before the transfer of electrons. What is net charge of the pair of objects after the transfer?
 
  • #10
DubbzWubbz said:
If both q1 and q2 are neutral, there would be no attraction? I assume I am transferring electrons to create a charge.

(GMm)/kq2 = |q1| q1 is proportionate to GMm/k multiplied by 1/q2. Would q2 be the charge of an electron?
There are certain units associated with q1 and q2. You must use these units for the Coulomb's Law equation to work properly.
 
  • #11
haruspex said:
Initially neutral, before the transfer of electrons. What is net charge of the pair of objects after the transfer?
The net charge wouldn't change because charge is conserved?
 
  • #12
DubbzWubbz said:
The net charge wouldn't change because charge is conserved?
Right, so what relationship does that give you between q1 and q2?
 
  • #13
haruspex said:
Right, so what relationship does that give you between q1 and q2?
q1 = q2?
 
  • #14
DubbzWubbz said:
q1 = q2?
Not quite. If the two charges are q1 and q2, what is the total charge?
 
  • #15
haruspex said:
Not quite. If the two charges are q1 and q2, what is the total charge?

Wouldn't the total combined charge be 0? this way they are balanced?
 
  • #16
DubbzWubbz said:
Wouldn't the total combined charge be 0? this way they are balanced?
Right, so express that as an equation in q1 and q2.
 
  • #17
haruspex said:
Right, so express that as an equation in q1 and q2.

Do I incorporate this into the previous equation I had?
 
  • #18
DubbzWubbz said:
Do I incorporate this into the previous equation I had?
In post #13 you wrote q1=q2. That is not quite right. I'm just trying to get you to the right version of that. You wrote, correctly, in post #15, that the net charge will be zero. Express that as an equation using q1 and q2. I'm not asking for anything obscure here, it's very straightforward.
 
  • #19
haruspex said:
In post #13 you wrote q1=q2. That is not quite right. I'm just trying to get you to the right version of that. You wrote, correctly, in post #15, that the net charge will be zero. Express that as an equation using q1 and q2. I'm not asking for anything obscure here, it's very straightforward.

Are you asking for simply q1q2 = 0
 
  • #20
DubbzWubbz said:
Are you asking for simply q1q2 = 0
That's so close I suspect a typo. Is that what you meant to write?
 
  • #21
haruspex said:
That's so close I suspect a typo. Is that what you meant to write?

q1/q2 = 0 Is this what you're looking for
 
  • #22
DubbzWubbz said:
q1/q2 = 0 Is this what you're looking for
No.
Consider any two objects. One has charge q1, the other has charge q2. What is the net charge? (Note: net charge is the same as total charge.)
 
  • #23
haruspex said:
No.
Consider any two objects. One has charge q1, the other has charge q2. What is the net charge? (Note: net charge is the same as total charge.)
q1 + q2 = 0
 
  • #24
DubbzWubbz said:
q1 + q2 = 0
Yes.
 

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