Question about formula for gravity

[Vay]

Gravitational force between two bodies is equal to G*m1*m2/d^2. Does this formula work for finding the force of gravity without interaction with another body? Such that the gravity of a single isolated body is equal to G*mass/d^2? Or does it have to require an interaction?

 

Also for F = M*a, this formula gives the instantaneous force at a particular location right? Is this the same for the force from G*m1*m2/d^2? Is gravity the only type of force that is affected by the inverse square law?

 

I don't learn the math yet, because I am still in a basic physics course. But fortunately there is this forum.

 

Thanks.

Edited September 23, 2011 by Vay

[mathematic]

When you leave out the mass of a second body, you are talking about a force field.

 

F=M*a is a force on an object, where it is located.

 

Electromagnetic force is also inverse square. The other two fundamental forces (weak and strong nuclear forces) are not.

[Janus]

Gravitational force between two bodies is equal to G*m1*m2/d^2. Does this formula work for finding the force of gravity without interaction with another body? Such that the gravity of a single isolated body is equal to G*mass/d^2? Or does it have to require an interaction?

[math]\frac{Gm}{d^2}[/math]

 

would give you the acceleration of an object at a distance of d from the center of mass 'm'. For instance, if d is the radius of the Earth, and m the mass of the Earth, you would get ~9.8 meters/sec called 1g.

It is generally what is used when you what to compare the gravity of two planets, Etc. because it doesn't depend on any other mass than that of the planet.

Also for F = M*a, this formula gives the instantaneous force at a particular location right? Is this the same for the force from G*m1*m2/d^2?

 

F=ma tells you how much force it takes to accelerate a given mass by a given acceleration

 

So for instance if we make m=m1, we can say that

 

[math]m_1a = \frac{Gm_2m_1}{d^2}[/math]

 

Since m1 appears on both sides of the equation, it cancels out leaving.

 

[math]a = \frac{Gm_2}{d^2}[/math]

 

Which is the formula for acceleration I gave above.

 

Is gravity the only type of force that is affected by the inverse square law?

 

No. The electromagnetic force also follows the inverse square law.

 

I don't learn the math yet, because I am still in a basic physics course. But fortunately there is this forum.

 

Thanks.