SIR WHY WE ARE NOT ABLE TO LIFT OURSELVES WITH HAND AND WHAT IS THE SCIENCE BEHIND THIS?

Dear Student,

Please find below the solution to the asked query:

According to Newton's Second Law, the rate of change of momentum is equal to the External Force. So,

$\frac{dP}{dt}=F_{ext}$

In the case, you mentioned, the force applied by the hand will be internal force. Because you are trying to lift one part of body with another. So, this is not an external force. So,

$F_{ext}=0$

Therefore,

$\frac{dP}{dt}=F_{ext}=0$

So, the momentum of the body remains constant and body will not move.

That is the reason why we have to apply an external force to lift our body. 

Hope this information will clear your doubts about the topic.

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Regards