The human body special mass

origin said:
Do you understand that physics says that the scale should only read a couple more kgf when you stand on your toes instead of an additional 60 kgf?
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You need to be specific. What are these couple kilogram-forces that the scale reads? does this mean I can exert any force I want to accelerate upwards any small acceleration I want and then return back to the ground with some huge work of 60*9.8*0.05 more than I exerted? The scale first reads 60 kgf, when lifting it rises to some 60+f kgf so indeed the force I exert is f kgf and this force cannot be any smaller force I want.
For any object placed for example on a table if I exert smaller forces than the weight the object will not accelerate upwards" I cannot lift it" as soon as the force reaches the smallest force greater than the object weight it will rise. For my body I exert smaller forces by my calf muscles to lift until I reach some force that can lift my body it is not an arbitrary force or any couple kilogram-forces.
 
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Yahya A.Sharif said:
You need to be specific.
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I was quite specific and showed you the calculation in post #50. Was there an error in the calculation? If you agree there was no error and yet you continuing to claim that the scale should read 120 kgf, then that would be trolling. If on the other hand you think there is an error in the calculation please point it out and we can discuss it.
 
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origin said:
I was quite specific and showed you the calculation in post #50. Was there an error in the calculation? If you agree there was no error and yet you continuing to claim that the scale should read 120 kgf, then that would be trolling. If on the other hand you think there is an error in the calculation please point it out and we can discuss it.
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It is simple, you assumed the distance 0.05 m and the time t 0.5 sec and you got 0.4 m/s/s as acceleration and 2.4 kgf as force by calf muscles to lift the body what if the force is less than 2.4 kgf or the acceleration is less than 0.4 m/s/s can the human for instance lift his body with 0.0003 kgf force by his calf muscles? if not what is the minimum force to lift my body and why?
 
Yahya A.Sharif said:
you assumed the distance 0.05 m and the time t 0.5 sec and you got 0.4 m/s/s as acceleration and 2.4 kgf as force by calf muscles to lift the body
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So you agree that the analysis was correct?
Yahya A.Sharif said:
what if the force is less than 2.4 kgf or the acceleration is less than 0.4 m/s/s can the human for instance lift his body with 0.0003 kgf force by his calf muscles?
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Yes.
As you probably know Newtons first law states that an object will not change it's motion unless acted on by a force. The reason that you don't move when standing on a scale is because there is no net force acting on you. You are putting 60 kgf on the scale and the scale is pushing 60 kgf against your feet for a net force of 0, so you don't move. If you were to exert 0.0003 kgf with your calf muscles you would very slowly raise up on the balls of your feet. Why would that happen? Because there would be the 60 kgf pushing down on the scale and there would be the normal force of the scale pushing up on your feet plus the force of your calf muscles for a total force of 60.0003 kgf. That would leave a net force of 0.0003 kgf or about 0.003 N upwards. Since F=ma, we can see that your acceleration upwards would be 0.003 N/60 kg = 0.00005 m/s^2, which is really slow over the distance of 5 to 20 cm.
Yahya A.Sharif said:
if not what is the minimum force to lift my body and why?
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Well the answer was yes not no. But to answer your question the answer is any nonzero net force will cause movement.
 
origin said:
Well the answer was yes not no. But to answer your question the answer is any nonzero net force will cause movement.
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First of all the calf muscles do not exert 60+2.4 kgf, the 60 kgf is the normal force of the body so apparently the calf muscles only exert 2.4 kgf which what appears on the scale by the calf muscles push force on the scale. The scale measures the weight 60 kgf added to it some force 2.4 kgf exerted by the calf muscles. As soon as the human lifts his body no normal force is acting on the heel. The only force acting is 2.4 kgf.

Second if I exert a 2.4 kgf by my muscles for a distance 0.05 m that is work done of 2.4*9.8*0.05=1.176 joules however when my heels returns back to the ground it exerts work of 60*9.8*0.05=29.4 joules you can see that I exert work less than the work I get which is violation of the law of conservation of energy so to conserve energy a minimum force of 60 kgf must be exerted “ the scale should read 120 kgf “ so that the work done is 60*9.8*0.05 equals the work gained by the heels when they return to the ground.
 
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Yahya A.Sharif said:
As soon as the human lifts his body no normal force is acting on the heel. The only force acting is 2.4 kgf.
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If that were true then you would have a net force of 67.6 kgf downwards and that means you would sink into the ground, since that doesn't happen you must be incorrect on this point.
Yahya A.Sharif said:
Second if I exert a 2.4 kgf by my muscles for a distance 0.05 m that is work done of 2.4*9.8*0.05=1.176 joules
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That is incorrect. Work is not force x acceleration x distance.
 
origin said:
That is incorrect. Work is not force x acceleration x distance.
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2.4 represents the force in kgf if you want to convert it into Newtons you multiply it by gravity acceleration 9.8 m/s/s so 2.4*9.8 is the force in Newtons.
You did not answer me :
If I exert a 2.4 kgf by my muscles for a distance 0.05 m that is work done of 2.4*9.8*0.05=1.176 joules however when my heels returns back to the ground it exerts work of 60*9.8*0.05=29.4 joules you can see that I exert work less than the work I get which is violation of the law of conservation of energy so to conserve energy a minimum force of 60 kgf must be exerted “ the scale should read 120 kgf “ so that the work done is 60*9.8*0.05 equals the work gained by the heels when they return to the ground.
 
origin said:
If that were true then you would have a net force of 67.6 kgf downwards and that means you would sink into the ground, since that doesn't happen you must be incorrect on this point.
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Oops, I meant 57.6 kgf.
 
Yahya A. Sharif:

Clearly, a person can stand and simultaneously hold another object, which means that the human body is quite capable of supporting more than its own weight. Human muscles are able to exert forces that are greater than the weight force on the body, too.

My impression is that you're unaware of these simple facts.
 
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I see what you were trying to do now Yahya, I will answer your question.
 
James R said:
Human muscles are able to exert forces that are greater than the weight force on the body, too.
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How do you know that ? Have you tried to lift a mass let's say 80 kg? I do not know how strong Origin is but when I put the scale I pressed as hard as I can with two legs and the scale measured 34 kgf I can lift my body like someone tries to pick a fruit from a tree with one leg easily without exerting my maximum strength. If one leg maximum strength exerts 17 kgf by calf muscles and because I lift easily without exerting my maximum strength then I lift my body with force less than 17 kgf.
 
Yahya A.Sharif said:
If I exert a 2.4 kgf by my muscles for a distance 0.05 m that is work done of 2.4*9.8*0.05=1.176 joules however when my heels returns back to the ground it exerts work of 60*9.8*0.05=29.4 joules you can see that I exert work less than the work I get which is violation of the law of conservation of energy so to conserve energy a minimum force of 60 kgf must be exerted “ the scale should read 120 kgf “ so that the work done is 60*9.8*0.05 equals the work gained by the heels when they return to the ground.
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Before we move on to energy balances you need to acknowledge that according to physics you should not see your scale read 120 kgf when you stand up on the balls of your feet. The reading should actually only be a little above 60 kgf, which is just what you read on the scale when you stand on your toes.
 
origin said:
Before we move on to energy balances you need to acknowledge that according to physics you should not see your scale read 120 kgf when you stand up on the balls of your feet. The reading should actually only be a little above 60 kgf, which is just what you read on the scale when you stand on your toes.
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Hi origin,
You will not find a solution for this, not because you do not have the physical knowledge but because it is something new.
The idea is if I lift with force let's say 1.5 kgf to a distance 0.05 meters my heels elapse, I am not doing a work of 1.5*9.8*0.05= 0.735 Joules but much bigger which is the energy taken from the body muscles that equals to 60*9.8*0.05= 29.4 Joules which is much bigger than 0.735 joules. To prove this, even though I exert only 1.5 kgf my muscles will be exhausted after only several repetitions of the movement because it exerted tiny force but did bigger work"energy from the body". However the muscles do not get that tired when exerting much bigger force like 15 kgf.
 
I guess me doing several repetitions of 250 kg's was a physical accident.
The universe simply glitched out.
Leg press machine of some sort in case people wondered if it was applicable to this thread.
 
Yahya A.Sharif said:
Hi origin,
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Hi, since you have not responded to my analysis, I will assume you agree with it. That means you agree that standing a scale and rising on the balls of your feet will cause the scale to move from reading 60 kgf to approximately 62 kgf, which is completely in line with mainstream physics.

Yahya A.Sharif said:
The idea is if I lift with force let's say 1.5 kgf to a distance 0.05 meters my heels elapse, I am not doing a work of 1.5*9.8*0.05= 0.735 Joules but much bigger
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Of course it's bigger! You are forgetting about the 60 kgf of your body.
When you are standing still on the scale your feet are supporting your weight or a force of 60 kgf. There is also a normal force of 60 kgf 'pushing' upwards against your feet. You don't move because the forces balance out. Standing is not very tiring because the force is mostly supported by your bones and not so much your muscles. This is why standing for 10 minutes is not tiring, however if you raise your heels up just a couple of cm your calf muscles will get tired in 10 minutes since they are now supporting the 60 kgf.

When you raise up on the balls of your feet how much force do your calf muscles feel? When standing with your heels just off of the scale your calf muscles have to balance the 60 kgf from you weight. To move up wards your calf muscles must supply some additional force. If we assume you move the distance very slowly this additional force is 1.5 kgf. So the force that your calf muscles are working against is 61.5 kgf not 1.5 kgf.

The problem here is that you thought you had found something missed by everyone else and that was a very exciting prospect for you. We have given you reason after reason why your ideas on this are wrong, but you are ignoring them because it is more exciting to cling to the idea that you are right. Unfortunately it has been shown that you are obviously wrong, it is long past time that you accept this and move on.
 
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Yahya A.Sharif said:
How do you know that ? Have you tried to lift a mass let's say 80 kg? I do not know how strong Origin is but when I put the scale I pressed as hard as I can with two legs and the scale measured 34 kgf I can lift my body like someone tries to pick a fruit from a tree with one leg easily without exerting my maximum strength. If one leg maximum strength exerts 17 kgf by calf muscles and because I lift easily without exerting my maximum strength then I lift my body with force less than 17 kgf.
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This is getting really silly now. It's obvious that human beings can lift a mass greater than their body weight. Look, here's a video of a man lifting 120kg:

https://www.youtube.com/shorts/8-bbxuAAlHg
 
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