system
Given the following post, respond as if you're commenting on Reddit:
human
My physics teacher reckons the "heavy and light objects fall at the same rate" demonstration only works below certain heights. Is there any truth in this?

I'm a trainee teacher, and I was doing a subject knowledge lesson in Physics today. The tutor told us about a demonstration showing that objects of different mass hit the ground at the same speed, using an empty whiteboard marker and one filled with sand. Pretty standard.

However, he cautioned us that if we did the demonstration from higher than the classroom ceiling (say, the roof of a 5-storey building), the demonstration wouldn't work - and the heavier pen would actually hit the ground first. We pushed him to explain, but all he could say is that it wasn't to do with drag or air resistance. Then he got distracted by a helicopter (don't ask).

Is there any truth in this? Is it possible that he WAS thinking about air resistance? Or is there any other explanation?
gpt
Air resistance will definitely cause things to fall at different rates, and have different terminal velocities - although that has more to do with the shape than the mass.

But he is absolutely incorrect in saying that, in the absence of air resistance, heavier things will start falling faster if you drop them from high enough.  Gravitational acceleration can easily be shown to be independent of mass in a first semester physics course.

Gravity:  F = GMm/r^2   
Newton's Law:  F = ma

Setting them equal, because the force of gravity is the force causing acceleration, gives:

GMm/r^2 = ma

m cancels, so

a = GM/r^2

Independent of the mass of the falling object, m.