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The red region I marked there the person hand is in contact with the block I want to know if there is any normal force acting between the person's hand and the block. If there is a normal force then what is direction of this normal force? If this person applies this force $F$ at an angle then will there be any normal force too?

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  • $\begingroup$ If the surface is frictionless then the person standing does not have any friction in their feet. If that person pushes, there will be a slight impulse (Force times contact time) before both person and block move in opposite directions and the F drops to zero. $\endgroup$ Sep 28, 2023 at 16:30
  • $\begingroup$ @StevanV.Saban That's rather irrelevant, they can still push the block by momentum conservation alone. Lack of friction doesn't mean the person can't push the block, it just means they'll move backwards when they do. Both begin to move the instant force is applied, and continue to accelerate while force is applied by the person's extending arm. There is no delay between application of force and movement. $\endgroup$ Sep 28, 2023 at 16:32

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The red region I marked there the person hand is in contact with the block I want to know if there is any normal force acting between the person's hand and the block.

If the person applies a force $F$ perpendicular to the surface of the block then $F$ is the normal force on the block. Per Newton's 3rd law the block exerts an equal and opposite force $F$ to the persons hands. If that force is perpendicular to the persons hands then $F$ is the normal force on the person's hand.

If there is a normal force then what is direction of this normal force?

The normal force is always the component of a force that is perpendicular to the surface.

If this person applies this force 𝐹 at an angle then will there be any normal force too?

Yes, but it will only be the component of $F$ that is perpendicular to the surface. If $\theta$ is the angle between the force and the surface, then the normal force is $N=F\sin\theta$.

Hope this helps.

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  • $\begingroup$ thank you very much and sorry for asking same question again and again $\endgroup$
    – user379089
    Sep 28, 2023 at 17:19
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The force labeled $F$ is the normal force from the hands acting on the block.

The word "normal" simply means "perpendicular to the surface" in this context. The force $F$ is perpendicular to the surface, so it is the normal force.

If the person applying the force is pushing at an angle, then you can still decompose $F$ into a perpendicular component and a tangential component. The perpendicular component is, by definition, perpendicular to the surface. So that component would be the normal force.

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  • $\begingroup$ the force F is muscular force? $\endgroup$
    – user379089
    Sep 28, 2023 at 16:36
  • $\begingroup$ and the person hand is in contact with block then there will be a normal force also so the net force on the block will be F+the normal force between person hand and block? $\endgroup$
    – user379089
    Sep 28, 2023 at 16:39
  • $\begingroup$ No the force on the block and the force of the man are in opposite direction , there magnitude is equal. $\endgroup$
    – trula
    Sep 28, 2023 at 16:58
  • $\begingroup$ @HarshitRaj It seems to me you have asked this before, perhaps under a different name (did you change your name on the site?) and were told not to double count the normal force. $\endgroup$
    – Bob D
    Sep 28, 2023 at 16:58
  • $\begingroup$ @Bob D i am very much cofused in normal force thatswhy i asked $\endgroup$
    – user379089
    Sep 28, 2023 at 17:03
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Adding to the other answers -

When the case is that only the block is on a frictionless surface - but the person is not (so the person can "push" the block without getting pushed backwards), even then there will be a normal force, which is the cause of the block's movement from rest.

To be more exact, the force will cause acceleration as long as it remains, which is very small here, because no matter the force, the block will move as there is no friction. So the contact will break from person's hands. And so there is no more normal force.

There onwards, the block will remain in constant motion as there is no force acting on it anymore, according to the Galileo's Law of Inertia (or the Newton's First Law).

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