is there some physical property that decreases proportional to distance^3

[iwantanewcomputer]

if i'm not mistaken gravity and em effects decreace proportional to r^2

 

[dowxp]

e- potential around a hydrogen atom? 1/r^2 ?

 

[Loki726]

I think your thinking of an equation that is multplied by a regular vector, not a unit vector. For example if R is a vector, and r is a unit vector along R, the following equations are the same:

r/|R|^2 = R/|R|^3

 

[silverpig]

The reason why is because flux is conserved through concentric shells. The ratio of the areas of the shells is 4*pi*R1^2 / 4*pi*R2^2. It's the flux through the area, and the area goes as r^2. That's why.

For something to go down as 1/r^3 you'd need to have either

a) a 4d field
b) some kind of attenuation that goes as 1/r (ie radiation from a star if the star is in a uniform gas cloud that absorbs light as 1/r)

 

[ahurtt]

ugliness?

 

[brentkiosk]

The field due to a dipole drops off as r^3.

 

[bobsmith1492]

Moments or second moments of inertia have interestingly cubed/quarted properties; I think there is a pi^3 and some sort of distance^4 in it, but it's been a while since statics class...

 

[msparish]

Tidal forces are proportional to 1/r^3

 

[silverpig]

Originally posted by: brentkiosk
The field due to a dipole drops off as r^3.

Ah! That's it.

 

[DrPizza]

Originally posted by: msparish
Tidal forces are proportional to 1/r^3

I had quickly googled the other day and saw that. However, there was only one link related to 1/r^3. Also, I would think that as tides are caused by gravitational forces, that it would be 1/r^2 and the only site I see with the former is wrong.

 

[msparish]

Originally posted by: DrPizza

Originally posted by: msparish
Tidal forces are proportional to 1/r^3

I had quickly googled the other day and saw that. However, there was only one link related to 1/r^3. Also, I would think that as tides are caused by gravitational forces, that it would be 1/r^2 and the only site I see with the former is wrong.

Decent explanation.
A simple explanation is to consider what causes the tides on earth: the moon. Despite the sun having a larger gravitational force on the earth, the dependence on r^3 causes the moon to be the body that causes tides.

 

[TuxDave]

Originally posted by: brentkiosk
The field due to a dipole drops off as r^3.

You are 1337! I forgot about that.

 

[DrPizza]

Originally posted by: msparish

Originally posted by: DrPizza

Originally posted by: msparish
Tidal forces are proportional to 1/r^3

I had quickly googled the other day and saw that. However, there was only one link related to 1/r^3. Also, I would think that as tides are caused by gravitational forces, that it would be 1/r^2 and the only site I see with the former is wrong.

Decent explanation.
A simple explanation is to consider what causes the tides on earth: the moon. Despite the sun having a larger gravitational force on the earth, the dependence on r^3 causes the moon to be the body that causes tides.

thank you.