Minimum period of rotation and gravity

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SUMMARY

The discussion centers on calculating the minimum period of rotation (T) for a planet with uniform mass density (ρ) to prevent it from flying apart due to centrifugal forces. The formula derived is T = (3π)^(1/2) / (Gρ)^(1/2). For a density of 5.5 g/cm³, participants are tasked with determining the specific value of T. The conversation highlights the importance of correctly applying the relationship between density, mass, and volume in the calculations.

PREREQUISITES
  • Understanding of gravitational constant (G) and its role in celestial mechanics
  • Familiarity with the concepts of rotational dynamics and centrifugal force
  • Knowledge of basic calculus, particularly derivatives
  • Ability to manipulate equations involving density, mass, and volume
NEXT STEPS
  • Calculate the minimum period of rotation for various densities using T = (3π)^(1/2) / (Gρ)^(1/2)
  • Explore the implications of rotational speed on planetary stability
  • Study the relationship between mass density and gravitational forces in astrophysics
  • Learn about the effects of rotation on other celestial bodies, such as stars and moons
USEFUL FOR

Astronomy students, physicists, and anyone interested in planetary science and the dynamics of rotating bodies in space.

Tonyt88
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Homework Statement


Consider a planet with uniform mass density p. If the planet rotates too fast, it will fly apart. Show that the minimum period of rotation is given by:

T = (3 pi)^(1/2)
...(G p)^(1/2)

What is the minimum T if p = 5.5 g/cm^3?



Homework Equations



T = 2 pi r
...v

v = (G m)^(1/2)
...(r)^(1/2)



The Attempt at a Solution



I combined the two equations to have:

T = 2 pi (r)^(3/2)
...(G m)^(1/2)

I found dr/dT to have:

3 pi (r)^(1/2)
(G m)^(1/2)

What am I doing incorrectly?
 
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How does dr/dT relate to this problem?

Read the question carefully, and try to use the "givens." In this case, you are required to find the minimum of period of rotation, which is given as a function of the velcocity.

Your substitution was right. Note that the planet's density is also provided. Remember that density = mass.volume
 
Hmmm, so am I not supposed to find a derivative somewhere, or?
 

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