Newton's third law - normal force

[Lori]

Homework Statement

A book is placed on a chair which is standing on the floor. An iPad is placed on the book. The floor exerts a significant force:

A) only on the book
B) Upwards on chair and downwards on book
C) ONLY upwards on chair
D) upwards on chair book and iPad
E) downwards on upad,book and chair
[/B]

Homework Equations

Third law, action reaction pair

The Attempt at a Solution

I was think it would be D) because the normal force has to be able to support the total weight of the chair, iPad, and book. But, I also think it could be C) because the normal force only acts on one object which can only be the chair.

Which is right and why?[/B]

 

[Orodruin]

Which objects are in contact with the floor and can therefore exert a contact force on it?

 

[I like Serena]

Hey Lori! :)

Extending a little bit on @Orodruin's response, there is a difference between the magnitude of a force and the object that a force acts on.
Which one is the problem statement asking for?

 

[Lori]

Hey Lori! :)

Extending a little bit on @Orodruin's response, there is a difference between the magnitude of a force and the object that a force acts on.
Which one is the problem statement asking for?

I think i understand now! So, the problem isn't asking for the magnitude of the force that is a result of the three objects, but it is asking for the object that this force is acting on.. so all this magnitude of force is acting on the contact object which is only on the chair. Is the key word significant? (if it was asking this way: what magnitude is the floor applying on the chair, it would be the sum of the objects?)

So, in the end, the normal force is always acting on the object that it's in contact with? But it doesnti necessarily equal to the weight of the object?

 

[I like Serena]

Yep. All correct!
The word 'significant' in front of force is redundant though. It doesn't tell us anything useful, and seems to only distract us.

 

[Orodruin]

The word 'significant' in front of force is redundant though. It doesn't tell us anything useful, and seems to only distract us.

I disagree. I believe it is there to avoid smarty pants students saying that all objects affect all other objects gravitationally.