FBDs for Box and Magnet Lifting by a Rope Attached to Ceiling

AI Thread Summary
In the discussion about free body diagrams (FBDs) for a box lifted by a magnet from the ceiling, participants clarify the role of normal forces. It is established that a normal force only exists when there is direct contact between surfaces. Since the box is not in contact with the ceiling, no normal force should be included in the FBD. Instead, all relevant forces acting on the box and magnet should be represented, excluding any non-existent normal forces. The conversation emphasizes the importance of accurately representing forces in FBDs based on physical interactions.
cmkc109
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Homework Statement



A box is lifted by a magnet suspended from the ceiling by a rope
attached to the magnet as illustrated in Fig 3.65. Draw free body
diagram for the box and for the magnet

so the picture is basically there is a ceiling , and the rope hanging from the ceiling to the magnet, and the magnet is attached to the box (located below the magnet)

I am wondering, will there be a normal force in the FBD since the ceiling is the surface? but wouldn't the Fn and Fg be in the same direction? or will it be no Fn because the object and the surface are not in direct contact?

Homework Equations





The Attempt at a Solution

 
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For every force there is an equal in magnitude and opposite in direction reaction force. "Normal force" is a name usually given to a particular kind of reaction force. Using that name in other contexts might be confusing. So, yes, there are reaction forces, but you probably shouldn't call them "normal forces".
 
tms said:
For every force there is an equal in magnitude and opposite in direction reaction force. "Normal force" is a name usually given to a particular kind of reaction force. Using that name in other contexts might be confusing. So, yes, there are reaction forces, but you probably shouldn't call them "normal forces".


so do u include it in the FBD?
 
what i am trying to ask it, should this force be included when the object is not in directly contact with the surface
 
You use all forces in the diagram.
 
cmkc109 said:
what i am trying to ask it, should this force be included when the object is not in directly contact with the surface
If the object is not in contact with the surface, there can be no normal force between them. Since it doesn't exist, you wouldn't include it.
 
ψ
Doc Al said:
If the object is not in contact with the surface, there can be no normal force between them. Since it doesn't exist, you wouldn't include it.

thanks for ur reply!
 
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