potential energy vs electrostatic force magnitude eq

[ihatebluescrubs]

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Hi,

Quick question about electrostatic forces:

The potential energy equation is U=KqQ/r
The electrostatic force magnitude is F=kqQ/(r^2)

I don't quite understand when you would use the two different equations. Why is the equation for potential energy only r and not r^2?

 

[LoLCareerGoals]

Obviously energy and force are not the same quantities, why would you expect them to be same?
You don't really need to understand how these formulas come about for MCAT, just memorize them.

I can tell you that 1/r^2 relationship typically stems from "density" of some quantity being reduced according to a rule of an expanding sphere. But I wouldn't worry about stuff like that.

 

[ihatebluescrubs]

Thanks for your help. One thing I don't quite get is the different between potential energy vs the electrostatic force magnitude. When would you choose to use one over the other?

 

[nickelbackfan]

Thanks for your help. One thing I don't quite get is the different between potential energy vs the electrostatic force magnitude. When would you choose to use one over the other?

well this is the same question as whats the difference in force on an object and potential energy of an object


say you have an object that is at a certain height in air. You can use PE=mgh to find its potential energy.

Also, there is a force that is exerted on the object (gravity).... F=ma.

As the object falls, gravity is constant acting on the object while the type of energy is changing from potential to kinetic.

You can relate this to two oppositely charged particles separated at a certain distance. They have a potential energy at that certain distance. They also want to attract each other. The thing causing this attraction is the force.

I guess its like comparing apples to oranges

 

[sciencebooks]

Thanks for your help. One thing I don't quite get is the different between potential energy vs the electrostatic force magnitude. When would you choose to use one over the other?

I've never seen any ambiguity in what they're asking for on the MCAT. They'll ask about one thing or another because as nicklebackfan suggested, they're something like apples and oranges when it comes down to what they're asking for.