One of the worst things we do to students is try to convince them (through any means necessary) that objects fall at the same rate. I think we do this to them in the name of stamping out misconceptions, but I believe it is high up on the damaging things we do to introductory physics students. I believe some of us do it because we think it really is cool, but mostly in doing so, we steal the possibility of it ever being cool for students.
I think it is damaging for a couple of reasons:
We mascarade around with one or perhaps a few demonstrations, and propagate the myth that single (or few) experimental outcomes determine truth.
We attach this observation or decree to the value of “g”, long before students have a chance to even understand what acceleration means.
We tell the lie that mass doesn’t matter for falling objects, when it fact it does, doubly so. It influences both the gravitational force and the intertial response of the mass to net force. It is the interesting intersection of these two truths (along with certain approximations) that something like mass doesn’t matter emerges. [Aside: The canceling of m’s across an equal sign is an injustice to the grounding and coordination of ideas that’s really involved.]
We fail to let them in on the interesting and perplexing conundrum of how it might even be possible for objects of different masses to always move the same way. The conundrum of “Man, I know it’s harder to get the more massive objects moving. So how does the gravitational force “know” to pull harder on the more massive one and to pull less hard on the lighter one? Or I know that the more massive object is being pulled down harder, shouldn’t it fall harder too?” That is where I want my students to be… in it. In the conundrum, misconception or not.
We rig contraptions to prove our point about freefall in a vacuum, long before our students are even poised to understand how that contraption could possibly work and before they’ve had a chance to think about why one would even care to do physics in vacuum. Isn’t there enough physics around us without vacuums?
I believe we kill the patient to cure them of an ailment they never knew they had.