To understand why the galaxy rotation curve in Part D is flat, we must first understand how gravity determines the orbital speeds of stars around the galactic center. Consider any star on a circular orbit around the center of the galaxy. The speed of the star's orbit depends on the star's distance from the galactic center and .

they should be similar or the same

air exerts forces on falling objects near earth’s surface.

explanation:

the term 'free falls' refer to object that are falling towards the earth, in a situation in which gravity is the only force acting on the object.

for an object in free fall, the acceleration is constant (g, the gravitational acceleration), and so the velocity of the object constantly increases.

for objects near earth's surface, there is always another force acting on the object: the resistance due to the air. this force is opposed to the direction of fall of the object, and it is proportional to the velocity of the object, so as the object falls down, this force increases up to a point when it balances the force of gravity, and the object continues its motion at constant velocity (called terminal velocity). since in this case gravity is not the only force acting on the object, we are not in a situation of free fall.

answerdmitry mendeleyev made a workable classification of the elements