A drum is rotating uniformly and on its inner side a body is rotating with it as well. enter image description here

I know by applying newtons law, a normal force has to exist and I can calculate that but my question is why should it exist? I cannot visualise the body pushing radially outward on the drum which leads to the normal force.

Let's focus on the element which is in contact with the body. Both of them have the same tangential speed . And for an instant they will move in unison without the body pushing radialy out. Then how does a normal force exist.

I'd be glad if someone pointed out. Thank you


Consider what would happen if the normal force was not there. The person would simply move outwards, due to his inertia.

Now because there is a wall there, the person will not be moving radially outwards. Instead, the person will apply a force on the wall, and by Newton's third law, the wall will apply an equal and opposite force on the person.

  • $\begingroup$ If this is unclear, I can include a sketch. Let me know. In my experience, this does cause a bit of confusion to students seeing it for the first time. $\endgroup$
    – user256872
    Jan 6 at 6:10
  • 1
    $\begingroup$ Thank you so much. $\endgroup$
    – Kashmiri
    Jan 8 at 9:55

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