Easy math question... Calculating radius of a sphere

[Wyck]

How do you calculate the radius of a sphere given the weight and density?

 

[minendo]

Density in what terms?

 

[gopunk]

well from that you can figure out volume right, then you reverse engineer the volume formula for a sphere

 

[Wyck]

pounds per cubic feet

 

[minendo]

Volume = 1/d x wt. From there follow gopunks advice.

 

[AgentEL]

is weight the mass or is it the force of gravity on the mass?

 

[ElFenix]

4/3 pi r^3 is volume of a sphere i believe.

 

[Wyck]

Hmm, I have here that

weight = density + 4 * pi * radius^3 / 3

 

[Martin]

find out how many cubic feet, then use the formula V = 4/3 pi r^3 to find out r.

 

[ElFenix]

Originally posted by: AgentEL
is weight the mass or is it the force of gravity on the mass?

the second...

 

[her209]

force = mass x grav

mass = force / grav

==================

density = mass / volume

volume = mass / density

==================

volume (sphere) = (4/3) x pi x r^3 (i think)

r = [3 x volume (sphere) / (4 x pi)]^1/3

================== combining them gets you

r = [3 x ((force / grav) / density) / (4 x pi)]^1/3

where:
force = weight (given)
grav is a constant
density (given)
pi = 3.14

 

[minendo]

Originally posted by: Wyck
Hmm, I have here that

weight = density + 4 * pi * radius^3 / 3

Then why are asking. That is pretty damn self explanatory.

 

[Wyck]

Because I forget how to divide/multiple to get r on the left. Look, math really isnt' my thing.

 

[PicPop]

this is soo hard

 

[gopunk]

Originally posted by: Wyck
Hmm, I have here that

weight = density + 4 * pi * radius^3 / 3

yea that is basically all the steps rolled into one equation.

 

[minendo]

Originally posted by: Wyck
Because I forget how to divide/multiple to get r on the left. Look, math really isnt' my thing.

Subtract density from both sides. Divide both sides by 4pi. Multiply both sides by 3. Take the cube root of both sides.

 

[AgentEL]

Originally posted by: Wyck
Hmm, I have here that

weight = density + 4 * pi * radius^3 / 3

that doesn't make sense because rearranging...

weight - density != 4 * pi * radius^3 / 3 = Volume of a sphere

 

[Sukhoi]

Originally posted by: Wyck
Hmm, I have here that

weight = density + 4 * pi * radius^3 / 3

No, mass = density * volume.

 

[Wyck]

I don't need to do the cube root of everything, radius^3 will be enough. So is this right?

radius^3 = weight - density - 4 / pi * 3

How would I group the numbers on the left?

radius^3 = (weight - density - 4) / pi * 3?

 

[nd]

Wyck, that doesn't look right.

If you're allowed to leave it in the form of r^3, I got:

Volume = (W/g*D)
R^3 = (3*volume) / (4*pi) = (3 * (W/(g*D)) ) / (4 * pi)

where W = weight, g = gravity (9.8 m/s/s on Earth), D = density.

 

[Wyck]

That will work. Thanks a bunch!!

 

[her209]

Originally posted by: Wyck
That will work. Thanks a bunch!!

If you had bother to read the thread, I practically gave you the answer above.