[Bored chemist]

You are failing to understand the nature of reality here.

Doubling the load 120 kg must not give the big difference but it did,

You have that the wrong way round.
Doubling the load does  make a big difference.
You can tell- because it does.
You should  look at the evidence.
The evidence says that you weigh 60Kg and you can jump around. So your muscles can carry 60Kg easily.
But that your muscles are not able to carry you  and another 60Kg  making a total of 120 Kg easily.

Why don't you just accept that 120 is a lot more than 60?

[Yahya A.Sharif (OP)]

The evidence says that you weigh 60Kg and you can jump around. So your muscles can carry 60Kg easily.

You didn't add this: my experiments say: as I can jump around easily I can lift my body with small force x*9.8 N too.

Why don't you just accept that 120 is a lot more than 60?

Soon or later you will know the truth.

[Bored chemist]

I can lift my body with small force

You keep saying that.
It is not true.

Soon or later you will know the truth.

We do know it.
We are just waiting for you to catch up with us.

[Kryptid]

Doubling the load 120 kg must not give the big difference

You think that doubling the weight that your legs must carry shouldn't make a big difference? That makes no sense at all.

[Yahya A.Sharif (OP)]

Doubling the load 120 kg must not give the big difference

You think that doubling the weight that your legs must carry shouldn't make a big difference?

It shouldn't make that big difference of jumping fast against gravity and barely moving the rock

[Kryptid]

It shouldn't make that big difference of jumping fast against gravity and barely moving the rock

Okay, prove it (and do it with an actual, good argument, not mere intuition).

[Bored chemist]

It shouldn't make that big difference of jumping fast against gravity and barely moving the rock

Again, you are looking at the experiment and ignoring what it tells you.
It obviously DOES make a big difference.
And yet you refuse to accept the evidence of your own senses.

[Kryptid]

Do you work out, Yahya? Try doing squats with no weight, then try using a squat machine with a mass equal to your own as the resistance. Report back on your findings.

[Yahya A.Sharif (OP)]

Do you work out, Yahya? Try doing squats with no weight, then try using a squat machine with a mass equal to your own as the resistance. Report back on your findings.

Hello
Unfortunately We don't have the machine in my country.

[Bored chemist]

Do you work out, Yahya? Try doing squats with no weight, then try using a squat machine with a mass equal to your own as the resistance. Report back on your findings.

Hello
Unfortunately We don't have the machine in my country.

Then accept the findings of someone like Kryptid who does have access to such machines.

Or just get a sack with 60 Kg of sand, put it across your shoulders and try doing squats.
There's nothing magical about the machine.

[Yahya A.Sharif (OP)]

Then accept the findings of someone like Kryptid who does have access to such machines.

What are his findings?

[Yahya A.Sharif (OP)]

Do you work out, Yahya?

If I lift my body 60 kgf alone I will exert x kgf. If a weight of 60 kg is on my shoulders I will need an x kgf for my body and 60 kgf for the other mass I will lift my body and the rock with 60+x kgf.  According to what you say  to lift the rock  I need 60 kgf to lift my body and a 60 kg to lift the rock a total of 120 kg.
First of all the scale will not show a 60 kg for lifting the body it will show  smaller than this " x kgf"
 Second we will have  two scenarios:
 The person lifts his body alone with  x kgf and lifts both the rock and his body with 60+x kgf. What I say
Or the person lifts his body with 60 kgf and lifts the rock with 60 kgf a total 120 kgf what you say.
The scale shows the lifting force is x kgf. The difference between 60+x/x lifting the body alone x kgf and lifting both 60+x kgf is far greater than the difference 120/60 lifting the body alone 60 kg and lifting both 120 kg. I only doubled the weight.

[Kryptid]

This is hopeless...

[Bored chemist]

Then accept the findings of someone like Kryptid who does have access to such machines.

What are his findings?

THAT YOU ARE WRONG!

[Bored chemist]

If I lift my body 60 kgf alone I will exert x kgf.

Yes.
x =60.
That's it.

[Bored chemist]

If a weight of 60 kg is on my shoulders I will need an x kgf for my body and 60 kgf for the other mass

Yes.
And x is still 60

[Bored chemist]

First of all the scale will not show a 60 kg for lifting the body

Yes it does.

[Dave Lev]

my experiments say: as I can jump around easily I can lift my body with small force x*9.8 N too.

Sorry to jump in.
However, what is so unique in your jump?
I can offer you several animals with a similar mass that can jump and lift much better than you do.
So why do you focus on the human body mass?
Why don't you focus on the human brain ability/mass?
Just think about it - You won't find any creature/animal in the entire planet that would claim that its body mass is special.

[hamdani yusuf]

According to what you say  to lift the rock  I will need 60 kgf to lift my body and a 60 kg to lift the rock a total of 120 kg.

Your soles lift that amount. Your knees lift less, since they don't lift your lower legs.
Your waist lifts less, because it doesn't lift your body parts below it.
If you lift the rock using your hands, your head doesn't lift anything.

[Yahya A.Sharif (OP)]

It shouldn't make that big difference of jumping fast against gravity and barely moving the rock

Okay, prove it (and do it with an actual, good argument, not mere intuition).

A person stands on a scale he holds a15 kg block on his hands and his arms are stretched out in front of his body  in which his arms make a lever its fulcrum is at the elbow. The position is equivalent to trying to pick a fruit  on a tree in which the fulcrum is at the toes . If he lifts the rock up as a lever the scale will read 15+60 kg that is the 15 kgf is the force he lifts the rock with which equals to the mass of the rock 15 kg. As the rock 15 kg needed 15 kgf, a rock of 60 kg will need a 60 kgf.
Lifting the rock will need a 60 kgf lifting or jumping with his body will need a very smaller force x kgf.  That why he can jump fast against gravity but he will barely move a rock of 60 kg.