Does Gravity Depend on ratio of mass? equation inside

[sigh hens]

I'm no physicist but this really doesn't make sense to me.

 

 

Simple newtonian physics says that gravity is dependant on mass and that an object with more mass will have more gravity, right?

 

well here's an equation I'm sure most of you are familiar with...

 

F = G*m1*m2/r^2

 

heres my problem...

 

m1 = 20

m2 = 1

r = 10

 

then F will = .2G

 

another example...

 

m1 = 19

m2 = 2

r = 10

 

then F will = .38G

 

 

In each example the mass of m1 and m2 add up to 21 and yet the gravitational force (F) is different. What is the rationale behind this? I thought all objects with the same mass had the same gravitational force no matter how you diveded them (assuming the same r value).

[Edge]

That's because 20*1 does not equal 19*2. Note that it is a multiplication not an addition.

[sigh hens]

I realize that but I thought objects that have the same mass were supposed to have the same force caused by gravity (assuming the same r value).

 

and that two objects that add up to the same mass as two other objects should both have the same Fgrav (assuming the same r value)

[Erasmus00]

I realize that but I thought objects that have the same mass were supposed to have the same force caused by gravity (assuming the same r value).

 

and that two objects that add up to the same mass as two other objects should both have the same Fgrav (assuming the same r value)

 

Two different objects falling toward the same body (i.e. a bowling ball and a nickle falling toward the Earth) should have the same accleration, not the same force.

 

Fgrav = -G*(Mass of the Earth)*(Mass of the object)/r^2.

Accleration = (Force on the object)/(Mass of the object) = -G*(Mass of the Earth)/r^2.

 

So all objects falling toward Earth accelerate at the same rate (it only depends on the mass of the Earth)

-Will

[arkain101]

Yah gravity is so strange.

It is a relationship effect between all mass.

The Amount of mass of an object means nothing in the gravity force it applies to an object but rather the density of space to matter ratio per given volume and yet the relationship is always the same acceleration.

Two chunks of chalk dont seem to pull much togther, but they do, but if we densify these objects (squeeze out the space-time inside them) the force they can apply to eachother grows and grows. Strong nuclear forces are dense, close relationship matter, could it be gravity is the force of all the forces of nature, but has several different faces because of several different relationships between the matter.?

 

what is the r in this equation F = G*m1*m2/r^2 ?

distance between objects or the radius of each object.?

[CraigD]

I realize that but I thought objects that have the same mass were supposed to have the same force caused by gravity (assuming the same r value).

 

and that two objects that add up to the same mass as two other objects should both have the same Fgrav (assuming the same r value)

I think you’re confusing 2 closely related, but distinct, Physics concepts (force and acceleration), and misunderstanding the context of a famous observation.

 

When we speak of 2 object experiencing the same acceleration (not force) due to gravity, regardless of their masses, we’re speaking of their acceleration due to the force of gravity between them and a third (usually much more massive) object. Recalling the fundamental definition of acceleration,

A = F / M,

we have, for 2 objects of mass M1 and M2, accelerated toward a third object of mass M3,

F1,3 = G* M1 * M3 / R1,3^2,

F2,3 = G* M2 * M3 / R2,3^2,

A1 =G* M3 / R1,3^2,

A2 =G* M3 / R2,3^2.

 

So, if R1,3 = R2,3, A1 = A2,

confirming the famous observation that a heavy object and a light objects dropped from the same height reach the ground in the same time (ignoring air resistence).

 

Although the gravitational force experienced by object 1 and 3 is the same, the acceleration is not:

A1 =G* M3 / R1,3^2

A3 =G* M1 / R1,3^2, confirming the observation that a small body moves toward a large one faster than the large one toward the small, such as when one releases a stone to fall toward the Earth (not only does the stone move toward the Earth, the Earth actually moves very slightly toward the stone).