# Coulomb's law vs. Newton's law of gravitation?

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What would be the easiest way to describe the similarities and differences between the two laws, other than the fact that their formulas are built similarly and they use different measurements. Any input would be great; I am currently having a brain block!

Coulombs Law:F=K (q1*q2)/r^2
Newtons 3rd Law: F=G(m1*m2)/r^2

## Answers and Replies

Simon Bridge
Science Advisor
Homework Helper
Hint: is Newton's Gravity ever repulsive? What about the electrostatic force?
You can also just google "comparison coulomb newton"

Hint: is Newton's Gravity ever repulsive? What about the electrostatic force?
You can also just google "comparison coulomb newton"
Thanks Simon, I have tried googling it and I didn't get quite the answer I was looking for.

Notice how enormous the value of Coulomb's constant is compared to the gravitational constant.

Simon Bridge
Science Advisor
Homework Helper
Oh? I found a whole lesson that lists similarities and differences and a raft of discussions on the same. More than enough to construct your own answer.
What sort of answer were you looking for?

Did you have a go following the hint given in the same post, the one in post #4?

Orodruin
Staff Emeritus
Science Advisor
Homework Helper
Gold Member
Notice how enormous the value of Coulomb's constant is compared to the gravitational constant.

The constants have different units and thus cannot be compared directly. I could easily define a set of units where the numerical value of the gravitational constant is orders of magnitude larger than Coulomb's constant. The relevant comparison would come from comparing, e.g., the gravitational force between two electrons to the electric force between the same electrons. This would be a comparison of forces, and thus be independent of the units chosen.

• Brian S. and PFuser1232
gneill
Mentor
What would be the easiest way to describe the similarities and differences between the two laws, other than the fact that their formulas are built similarly and they use different measurements. Any input would be great; I am currently having a brain block!

Coulombs Law:F=K (q1*q2)/r^2
Newtons 3rd Law: F=G(m1*m2)/r^2
Newton's 3rd Law of motion is not the law of gravitation. The third law is the law of action and reaction. The law of gravitation is a different beast altogether.

Can you list the points of similarity and dissimilarity that you have uncovered?

You can also think about the inputs (q1 q2 vs m1 m2), discussing how the signs of the quantities have physical significance