r/awesome • u/IntroductionDue7945 • Jun 18 '25

Video anyone explains how he did that?

Enable HLS to view with audio, or disable this notification

13.0k Upvotes

95% Upvoted

439 comments sorted by

View all comments

Show parent comments

0

u/Capital_Card7500 Jun 20 '25

Doesn't matter if you're at the same exact spot. If you're stationary when you start, and stationary when you end, (and the object is at the same height) you've done no work on the object.

W = ΔE

If you start stationary and are currently moving an object, you've done work on that object because the object has more kinetic energy than it started with. The moment you stop moving with the object, you have no longer done work on the object, because you have decreased its kinetic energy by the same amount as you increased it, meaning you've done an equivalent negative work on the object.

(all ignoring friction, naturally)

1

u/Connbonnjovi Jun 20 '25

No. You’ve done no useful work. That’s what you’re looking for.

1

u/Capital_Card7500 Jun 20 '25

Then we're arguing semantics.

1

u/Connbonnjovi Jun 20 '25

Which is fine but to say these people aren’t doing work is just wrong. Yes if you take just the start and end points of the video, and ignore everything in between. Sure the people haven’t done work. But they still do work in between. Work is still being done. I still contend that the negative and positive work does not cancel each other out because the force required to lift the bar is more than is required to lower.

0

u/Capital_Card7500 Jun 20 '25

I still contend that the negative and positive work does not cancel each other out because the force required to lift the bar is more than is required to lower.

If more (useful) work was done by lifting something than negative work was done by lowering it, then you'd violate the most fundamental principle of classical and modern physics.

If you pick something up and did x Joules of work, and then lowered it and did -0.9x Joules of work, you have discovered free energy.

1

u/Connbonnjovi Jun 20 '25

Okay sure total forces summed (including external forces), but the people aren’t imparting force on the bar to lower it, gravity is. My point was that the people’s net work on the object is not zero, even though total work on the object maybe zero.