Explain why stars form only in molecular clouds, the coldest, densest parts of the interstellar medium
What will be an ideal response?
A cloud collapses and ultimately forms stars when gravity overcomes thermal pressure. The latter depends both on the density and temperature of the cloud. The high densities in molecular clouds means that the gravitational forces are relatively strong but the pressure is no higher than elsewhere because the temperatures are low.
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If, in the figure below, I1 = 2 A and I2 = 6 A, which of the following is true?
A comet in a highly elliptical orbit is found to have a semimajor axis equal to one astronomical unit (AU). According to Kepler's 3rd law, what would be the sidereal period of this comet?
a. more than one year b. one year c. less than one year d. 76 years; the same for every comet e. Not enough information is given to determine this.
A cube is subjected to a pressure of 12 atmospheres. The un-squeezed length of one side of the cube is 10.000 cm. The squeezed length of one side of the cube is 9.999 cm. The bulk strain on the cube is
a. 
b. 
c. 
d. 
e. 
A uniform sphere of radius R and mass M rotates freely about a horizontal axis that is tangent to an equatorial plane of the sphere, as shown below. The rotational inertia of the sphere about this axis is
?
?
a.
.