Originally Posted by C₄H₁₀
It's baffling that this still exists.
I mean, I understand that it defies some basic sensory logic and I can see where some people wouldn't immediately recognize what's going on, but I completely fail to comprehend how they can still not get it after it's been explained. Analogies, thought experiments, mental models... None of it seems to work.
I guess some people don't/can't believe what they can't see for themselves. I work at a Uni and some students have difficulties with certain behaviours of electrical systems until they can be provided with a suitable mechanical analogue then the light comes on and they "see" what's going on.
To be honest, the blame lies partly with the educational system when students are taught physics by some "kid" that scraped a pass on his physics course during his teaching degree and whose probably forgotton half of that already.
The lack of understanding of what the kinetic energy calculations are actually useful for come about because of the silly, simplified questions students in high school are asked about cars hitting walls. Students then tend to walk away thinking kinetic energy is some fixed quantity that objects posess like 50 litres of fuel in a tank while not fully understanding that a plane circling a building at 1000mph has NO kinetic energy relative to a person standing on top of the building and a constantly varying kinetic energy relative to anything not located at the centre of the circle.
Anyway, it's like that math brain teaser about the Bellhop that has to give the customer back some change and he keeps a bit, and sombody else keeps a bit and suddenly all the amounts don't add up to the original quantity anymore. When you do the math wrong, of course the answer doesn't make sense...