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Imagine a falling body, that is in a tube. The tube and body may have a frictional coefficient $\mu$. Generally the frictional force would be given by $\mu R$, where $R$ is the normal reaction. But in this case, how does one calculate $R$? Clearly, there would be a force of friction, but how much?

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  • $\begingroup$ Why do you think it is applying a horizontal force in the first place ? $\endgroup$
    – Bhavay
    Commented Apr 27, 2021 at 12:46
  • $\begingroup$ @Bhavay it isn't, but it seems intuitive that the particles of the surface are resisted by the particles of the other surface if they are in contact. $\endgroup$
    – Sid
    Commented Apr 27, 2021 at 13:01
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    $\begingroup$ There is no way to calculate R , from the amount of information you have given. You need more data points to get that $\endgroup$
    – silverrahul
    Commented Apr 27, 2021 at 13:05
  • $\begingroup$ @silverrahul such as? $\endgroup$
    – Sid
    Commented Apr 27, 2021 at 13:05
  • $\begingroup$ Maybe , how fast it is falling . $\endgroup$
    – silverrahul
    Commented Apr 27, 2021 at 13:06

1 Answer 1

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It is true it seems intuitive that the block will feel a resistive force , since it is in contact and will face electrostatic force.

To calculate R ,I believe you need to know the acceleration of the block.

CAse1 : If acceleration is 0.

Then $mg = 2\mu R$

Case 2 If acceleration is non zero .

then $mg -2\mu R= ma$.

From there you can calculate R.

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