Need help with Normal forces?

Question

I'm trying to draw a free body diagram of a table that is placed on the floor. On the table there is math book. Then on the math book there is a chemistry book. Does the floor exert a normal force on all three....or just the table or math book or chem book

Answer 1

The normal force exerts on all 3.  When objects are stacked they essentially becomes one object with respect to the floor in this case.  

Then normal force from the floor would be exerted on all objects above it so by adding the rug it stills is exerting a normal force on the rug, the table and the math book.  

Hope this helps.

Answer 2

i would say that the normal force of the floor is only placed on the object closest to it. in the order that you show...the floor has a normal force on the rug, the rug on the table, the table on the math book, and the math book on the chem book.  

Answer 3

Floor applies normal force only on table. If you make FBD of table, then show normal force from floor. If you make FBD of math book, which is kept on the table, then do not show normal force from floor. Likewise, do not show normal force from floor in FBD of chemistry book.

But suppose that you want to treat table + math book together as a system. You want to draw FBD of this system. Then you should show the normal force from the floor. This is because the floor exerts normal force on the table. The table is a part of the system. The floor exerts normal force on the table. This means that it exerts normal force on the system.

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In case of rug on floor and chair on rug, the floor exerts normal force only on the rug.

To summarize, the floor exerts normal force only on the object in contact with the floor.