# Homework Help: Direction of Normal force

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1. May 17, 2017

### Faiq

1. The problem statement, all variables and given/known data

3. The attempt at a solution
Can somebody please assist me in finding the direction of the normal force exerted on B? (How is normal force at B also normal to the rod? )

There is no hint provided from which I can conclude the direction of normal force. Can somebody please provide a hint so I can work it out?

P.S

Contact force = Normal force since friction is 0.

2. May 17, 2017

### haruspex

3. May 17, 2017

### Faiq

If only one has a tangent plane (as in the picture), use that.

Can you please clarify this point?

My confusion regarding this:
Considering the diagram given on the section 1 of the reference page, if we were to move the rod at a very very small angle keeping the contact point constant, the direction of the normal force will remain same but it won't necessarily be perpendicular to the rod.

4. May 17, 2017

### haruspex

I do not understand your response. That section tells you how to figure out the direction of the normal force in a point contact like the one in this question. Isn't that what you wanted to know?

5. May 17, 2017

### Faiq

6. May 17, 2017

### haruspex

No, it would move exactly as the rod moves and remain perpendicular. Why not?

7. May 17, 2017

### Faiq

Oh. So no matter how the surface of contact is, if my rod is a straight rod the contact force will always be perpendicular to the surface of rod?

But this point will not apply for the edges of the rod right? Because the straightness ends over there?

8. May 17, 2017

### haruspex

Yes. It follows from the definition of normal force that I give at the start of the section.
It will not apply at the tips, no, because there is no well-defined contact plane there. Generally you will be able to figure out the contact plane from what the tip touches, as in the question above where it rests in the bowl.

9. May 17, 2017

### Faiq

Thank you very much.