Why do disk stars bob up and down as they orbit the galaxy?
because the gravitational pull of other disk stars always pulls them toward the disk because of friction with the interstellar medium because the halo stars keep knocking them back into the disk

The answer is "because the gravitational pull of other disk stars always pulls them toward the disk".

Explanation:

The disk stars bop up and down as they orbit the Galaxy because the gravity of other disk stars always pulls them toward the disk and not because of friction with the interstellar medium or even because of the halo stars keep knocking them back into the disk.

This disk is about 100 time wider than it is thick. This slight thickness is caused by the regular bobbing up and down of stars in the disk.

nec chapter 5 contains

c. information on special occupancy areas

nec chapter 6 covers

a. special equipment

which of the following rules contain the words shall or shall not and must be adhered to?

b. mandatory rules

which of the following rules identify actions that are allowed but not required and typically cover options or alternative methods?

c. optional rules

which of the following serves as the introduction to the nec and provides an overview of the book?

a. nec article 90

organizations that test products for safety are

c. nrtls

the nec is published by the

a national fire protection association

the nec is divided into

b. 9 chapters

the nec provides informative annexes for

c. informational materials and examples

two terms from nec article 100 that trainees should become familiar with are

b. labeled and listed

explanation:

the answer is b, have negligible mass