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A mass can be be lifted with force less than its weight


awaterpon
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According to classical mechanics for a force to  lift a mass it should be slightly greater than its weight .

My hypothesis  is that a human body can lift itself  by a force far less than its weight .

It is obvious phenomenon that when lifting an object  of 60 kg up , it would be extremely hard than lifting one's body " 60 kg" .while standing.

This applied to many phenomenon  .A body will seem to have inertia far less than its actual mass inertia , moving and walking effortlessly , standing effortlessly , lifting one's body parts easily.

In this special case the Newtonian equations doesn't apply , however we could measure the ratio between the force lifting a body and the force lifting an object both body and the object have the same mass.

Edited by awaterpon
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For one thing, a body is made of parts.

If you lift a 60 kg weight with your arm, the arm has to cope will all 60 kg.

A 60 kg person lifting themselves, does it in parts. Their neck lifts their head. Their core lifts their torso plus neck plus head. Their legs lift all the above.

It's not an apples to apples comparison. A 60 kg person doing a one-handed pull up or press up, would be a fairer comparison.

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46 minutes ago, pzkpfw said:

For one thing, a body is made of parts.

If you lift a 60 kg weight with your arm, the arm has to cope will all 60 kg.

A 60 kg person lifting themselves, does it in parts. Their neck lifts their head. Their core lifts their torso plus neck plus head. Their legs lift all the above.

It's not an apples to apples comparison. A 60 kg person doing a one-handed pull up or press up, would be a fairer comparison.

Thanks.

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45 minutes ago, Strange said:

Also, the total force on the ground will be exactly equal to the weight. And the force of the ground on the person will also be equal to that. So Newton is redeemed once again.

Thanks

It's unbelievable that I carry up my 60 kg body with only my feet when trying to pick  a fruit on  a tree.
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7 hours ago, awaterpon said:

According to classical mechanics for a force to  lift a mass it should be slightly greater than its weight .

My hypothesis  is that a human body can lift itself  by a force far less than its weight .

It is obvious phenomenon that when lifting an object  of 60 kg up , it would be extremely hard than lifting one's body " 60 kg" .while standing.

This applied to many phenomenon  .A body will seem to have inertia far less than its actual mass inertia , moving and walking effortlessly , standing effortlessly , lifting one's body parts easily.

In this special case the Newtonian equations doesn't apply , however we could measure the ratio between the force lifting a body and the force lifting an object both body and the object have the same mass.

In the low speed situations you describe Newton always applies.

If course it depends exactly what you mean

Mechanical Advantage = Load / Effort

and an ME of greater than 1 is certainly achievable with suitable arrangements.

Of course you need to go a long way further back than Newton for some of these, right back to the ancient Greeks.

"Give me a long enough lever and a fulcrum and I will lift the world."

 

https://en.wikipedia.org/wiki/Mechanical_advantage

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6 hours ago, awaterpon said:

 

It's unbelievable that I carry up my 60 kg body with only my feet when trying to pick  a fruit on  a tree.

Why do you find this unbelievable, when you have grown up with this perfectly normal experience?

It is like saying "It's unbelievable that I can breath the air around me" or "It's unbelievable that I can hear the range of sounds that my ears are specifically made to receive" or "It's unbelievable that water is wet" or any number of perfectly ordinary things.

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  • 1 year later...
Posted (edited)

 

These are other observations:

An average human can jump high raising his 60 kg weight while he barely moves a rock of 60 kg

A human can run fast with his massive 60 kg weight while he barely moves the same rock of 60 kg

A human can lift his body of 60 kg holding a bar many times but he will barely move a rock of 60 kg

This is an experiment of how a human can lift or moves his body mass with force less than the force needed to lift or move an equivalent mass:

The scale reads approximately 8 kg"80 N" which is the maximum force my calves' muscles can exert .So in the video for me to lift my 57 kg weight I should only use the maximum 8 kg"80 N" or less to lift my weight of 57 kg. This means in the video I only use 8 kg "80 N "or less to lift my massive body of 57 kg .

Video

Edited by awaterpon
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1 hour ago, awaterpon said:

 

These are other observations:

An average human can jump high raising his 60 kg weight while he barely moves a rock of 60 kg

 

These are not equivalent motions, so this comparison is not particularly useful

 

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3 hours ago, awaterpon said:

The scale reads approximately 8 kg"80 N" which is the maximum force my calves' muscles can exert .So in the video for me to lift my 57 kg weight I should only use the maximum 8 kg"80 N" or less to lift my weight of 57 kg. This means in the video I only use 8 kg "80 N "or less to lift my massive body of 57 kg .

It sounds like the scale is broken or there is an issue with the measurement. If your maximum force in a toe press exercise would be 80N then your would not be able to stand on your toes if your weight is 57kg. 

If you try to stand on your toes on a typical bathroom scale the scale shows your weight. 

 

(I have not watched the video)

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3 hours ago, swansont said:

These are not equivalent motions, so this comparison is not particularly useful

 

These are close:

I carry 20 kg rock and I jump compared to jumping with only my 60 kg weight 

Running while carrying the 20 kg rock vs running with only my 60 kg weight

20+60 kg will not give that significant difference 

21 minutes ago, Ghideon said:

If your maximum force in a toe press exercise would be 80N then your would not be able to stand on your toes if your weight is 57kg. 

In case I lift my body with small force the ground will push with the same small force the two forces will give slight pressure on the toes 

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8 minutes ago, awaterpon said:

In case I lift my body with small force the ground will push with the same small force the two forces will give slight pressure on the toes 

Your are affecting the ground with the force of your weight* and ground will push back with an equal and opposite force. Stating on your toes does not change that. Basic physics and something you can verify with a bathroom scale or a seesaw. 

*) m*g

 

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27 minutes ago, awaterpon said:

These are close:

I carry 20 kg rock and I jump compared to jumping with only my 60 kg weight 

Running while carrying the 20 kg rock vs running with only my 60 kg weight

20+60 kg will not give that significant difference 

And? This seems to be an argument against your thesis.

Further, running vs walking or jumping vs standing are more an issue of power, rather than force.

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Levers, gears and pulleys are all ways for less force to lift objects that weigh more (have greater gravity force) than that - a smaller force is applied through a longer distance. But the amount of energy expended will be (without friction) the same. What cannot be done is doing that whilst using less energy.

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Posted (edited)
1 hour ago, Ghideon said:

Your are affecting the ground with the force of your weight* and ground will push back with an equal and opposite force. Stating on your toes does not change that. Basic physics and something you can verify with a bathroom scale or a seesaw. 

*) m*g

 

If the two forces are weight and ground force that will appear in the toes pressure , the toes pressure is slight and 60 kg is massive to the toes or body to bear.Yet the scale reads the actual mass 60 kg and the gravity force is for a mass of 60 kg

Edited by awaterpon
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2 minutes ago, awaterpon said:

If the two forces are weight and ground force that will appear in the toes pressure , the toes pressure is slight and 60 kg is massive to the toes or body to bear.

I think we have had this discussion already*. The forces are as predicted by physics. Please draw a simple diagram with the forces you are uncertain about so that we can clarify the situation and correct misunderstandings.

I have assumed you mean the action/reaction forces floor<->person.If you wish to discuss forces in the foot we can probably do that using a simple model.

 

 

*) https://www.scienceforums.net/topic/121169-massive-human-body-can-stand-on-its-weak-feet-toes/?tab=comments#comment-1130639

 

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9 hours ago, Ghideon said:

I think we have had this discussion already*. The forces are as predicted by physics. Please draw a simple diagram with the forces you are uncertain about so that we can clarify the situation and correct misunderstandings.

I have assumed you mean the action/reaction forces floor<->person.If you wish to discuss forces in the foot we can probably do that using a simple model.

The model is not a proof. So could we discuss how what I propose violates physics predictions ?

 

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1 hour ago, awaterpon said:

The model is not a proof. So could we discuss how what I propose violates physics predictions ?

I have read the post again and it is not clear which force you refer to. Please clarify your proposal, a picture with the forces may be helpful?  Here is a quick example (my anatomy knowledge is limited; use picture as inspiration and not science facts)

image.png.031a32556d6e44df7e971d32571757db.png

 

16 hours ago, awaterpon said:

The scale reads approximately 8 kg"80 N" which is the maximum force my calves' muscles can exert .So in the video for me to lift my 57 kg weight I should only use the maximum 8 kg"80 N" or less to lift my weight of 57 kg. This means in the video I only use 8 kg "80 N "or less to lift my massive body of 57 kg .

Maybe you mean the maximum force calves' muscles can exert as a force "A" in the picture but you seem to measure and discuss force "B? 

 

edit: Disclaimer; length of arrows A and B are not an indictor of magnitude of forces, the example picture is not intended to correctly display how force A relates to force B, it's just an illustration to help the discussion.

Edited by Ghideon
clarifying arrow lengths
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Posted (edited)


Suppose I have another scale with a surface and a spring I stand on the surface to do the measurements by pressing the spring.

I refer to three forces :
1) The force I press on the spring surface to lift my body and it turns out to be 80 N as my scale reads in my experiment
2) The force gravity exerts downwards to be stored in the spring which turns out to be  the weight 570 N
3) The normal force the surface of the scale pushes upwards which equals the force I lift my body with " two forces in opposite directions"

If I stand on the scale I will do two things:
One I compress the spring with my 57 kg mass  by gravity force 570 N and the spring will store my weight 
The supposed normal force by the surface upwards equal to my weight doesn't exists in this case"for humans"

Second I will press the scale surface with my body mass but the mass here not equal to but equivalent to a smaller mass 8 kg so actually the surface pushes me with only 8 kg "80 N" and the force I lift my body with also small "the 80 N" 

When a body moves or lifts itself , body mass will be equivalent to a smaller mass, so inertia as well will be small"effortless walking and running" however force of gravity will be  for the actual mass. We can compare two equal masses on a two-legged scale one is an object 70 kg and the other is a body 70 k both will have the same gravity force  even though the body will have some equivalent mass
I hope this is more clear

Edited by awaterpon
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18 minutes ago, awaterpon said:

I hope this is more clear

Sorry, no. Please provide a picture with the forces and their point of application. 

 

19 minutes ago, awaterpon said:

The supposed normal force by the surface upwards equal to my weight doesn't exists in this case"for humans"

It sounds like you claim that the laws of physics as we know them are unable to predict the mechanical forces for a human standing on toes. More clarity is required to locate issues with measurements or possible misunderstanding.

Newtonian physics have known limitations but in the context of this thread the laws of Newton are applicable.

 

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