Aphysics student is presenting a report on a material that can conduct an electrical current with no resistance. she explains that the uses of this material are limited since the material has to be very cold when used. which best describes what the student’s report was about?
(a) superconductivity.
(b) solid-state physics.
(c) metallurgy.
(d) crystallography

this is poiselle's equation from fluid mechanic in physics. mech eng

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.