It seems that any physics lecturer worth his/her salt must perform this demonstration

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Walter Lewin did it.

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Paul Hewitt did it

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How can we not join in?

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The following one is quite scary to much if you know your physics…

The principle of conservation of energy is actually a very abstract concept. So it is amazing that we teach it to primary school kids. As a kid, I was taught that sound, light and electricity are all different forms of something called energy, which has this ability to morph from one form to another like a shape changer. It is also able to glide out of one body and slip into another, invisibly, like a ghost or spirit. I guess, as a kid, I didn’t have any problem accepting such a magical construct. Now that I am an adult, I realize that energy is a pretty bizarre idea. No one explains this better than Richard Feynman, in Section 4-1 What is Energy of the Feynman Lecture Series.

https://www.feynmanlectures.caltech.edu/I_04.html

Spoiler: At the end of the analogy, Feynman dropped the profound punch line: “There are no blocks.” The idea that energy is never an actual thing really blew my mind.

Everyone of them is exerting an upward force F on the weight. But is F doing positive, negative or zero work (on the weight)?

Because FΔs=ΔKE.

https://youtu.be/Wrmrg32udVU

Size does matter, when it comes to projectile weapons. The longer distance allows more work done, and results in higher KE of the projectiles.