[Origin]

You asked this question 5 years ago in this thread:
Can a mass be lifted with force less than its weight ?
The answer you received then was 'no', the answer is still 'no' and 5 years from now the answer will still be 'no'.

[paul cotter]

I think I know the error this poster is making. In a healthy person of ~70kg the nervous system has adapted to the work in, for example standing up from a seated position, and the process feels close to effortless. Now that same person is asked to lift 20kg and a significant effort is required because that is an extra load that his(her) neuromuscular system is not accustomed to. If one was to strap a 20kg to oneself it would be quite noticeable as requiring an extra effort to stand up. Left there over a prolonged period it would become unnoticeable as the neuromuscular system adapts to the new load. Good to see you posting again, Origin, best wishes from "da Grinch"

[Bored chemist]

The final theory is available at SSRN:
The Biological Leverage in Humans and Animals' Self-Movement
https://papers.ssrn.com/sol3/papers.cfm?abstract_id=4794848

https://www.quora.com/Is-the-journal-International-Journal-of-Applied-Science-and-Technology-a-good-journal-or-a-predatory-journal

[alancalverd]

Predatory and amateur.

[alancalverd]

I lift with my only feet muscles

There's the trick! No human has significant muscles in his feet. YAS is an octopus or an alien.

[Yahya A.Sharif (OP)]

It is SSRN, it is not a predatory journal it is not even a journal:
Biological Leverage in Humans and Animals' Self-Movement
https://papers.ssrn.com/sol3/papers.cfm?abstract_id=4794848

[Yahya A.Sharif (OP)]

I lift with my only feet muscles

YAS is an octopus or an alien.

Its along time since your funny comments, thanks Alan I actually adopted that acronym.

[Bored chemist]

it is not even a journal:

[evan_au]

A different take...

Can a mass be lifted with force less than its weight ?

Yes, if it is in a liquid to provide some buoyancy...
- and the weight is measured in air

That's why elderly people do "Aqua-Aerobics".

[Yahya A.Sharif (OP)]

A different take...

Can a mass be lifted with force less than its weight ?

Yes, if it is in a liquid to provide some buoyancy...
- and the weight is measured in air

That's why elderly people do "Aqua-Aerobics".

Hello Evan_au,
Yes it's true that doing that exercise will require less force, but the resultant force is the force by muscles plus the buoyant force  the same force when doing that outside water. A similar example is a mass balanced with a pulley; pulled upwards by another mass less in weight you will always lift the bigger mass with force less than its weight because it is pulled upwards by the rope by the smaller mass gravity.

[alancalverd]

No. The force in the part of the rope attached to the bigger mass is exactly the weight of the mass. A single pulley won't make life any easier but a multiple sheave block acts as a force multiplier: the small mass moves further than the big one and energy (force x distance) is conserved.

[Yahya A.Sharif (OP)]

I think you didn't get me. The pulley is free to rotate, the smaller mass is exerting force equals to its gravity on the bigger mass, so you need to exert force equals:
Mg-mg
M: mass of the bigger object
m: mass of the smaller object
Actually if the masses are equal, in theory you can exert the smallest force but to accelerate it in a short time to lift it you need to exert the force for the time you want. See the drawing.

[alancalverd]

Your wording was inexplicit and implied what I wrote.