Normal Force Between Block & Table: Free Body Diagram Explained

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Discussion Overview

The discussion centers around the concept of normal force between a block and a table, particularly in the context of free body diagrams. Participants explore the relationship between the normal force and the weight of the block, considering different scenarios such as horizontal and inclined surfaces.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants assert that the normal force is equal to the weight of the block when the table is horizontal.
  • Others propose that the normal force depends on the angle of the table, stating that it equals the component of gravity acting perpendicular to the surface when inclined.
  • A participant emphasizes the importance of including only the forces acting on the specified body in a free body diagram, noting common mistakes in this area.
  • One participant reiterates the equilibrium condition, stating that the normal force must equal the block's weight when at rest on a horizontal surface, while questioning the relevance of Newton's Third Law in this context.

Areas of Agreement / Disagreement

Participants express differing views on the conditions under which the normal force equals the weight of the block, particularly regarding the angle of the table. There is no consensus on the implications of Newton's laws in this scenario.

Contextual Notes

Some assumptions about the system, such as the absence of other forces and the specific conditions of the table's angle, are not fully explored or agreed upon. The discussion does not resolve the implications of Newton's laws in relation to the normal force.

starbaj12
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If there was a block on a table what would be the normal force between the block and the table. If you could describe the free body diagram that would be great too.
 
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The normal force between the block and the table is just the weight of the block.

A "free body diagram" would show the weight vector of the block acting downward on the table and an equal force vector acting upward on the block.
 
normal force

Assuming that the only other important force acting on the block except normal reaction is the force of gravity, then the normal force depends upon the angle of the table with the horizontal.

In the most probable case when the angle is 0 deg., the normal reaction is equal to the force of gravity in magnitude (but upwards), not because of Newton's third law but because of Newton's first law. Since, the block is not accelerating, forces on it must be balanced, so normal force has to be equal to the force of gravity.

In case the table is at an angle, normal recation is equal in magnitude to the component of gravity opposite to it.

spacetime
www.geocities.com/physics_all/index.html
 
I just wanted to say an important fact about the free body diagram, that makes students confused:
Just put the forses that ACTs on the specified body and not more!
It may seem very simple, but I have seen lots of mistakes about it.
Good Luck!
 
starbaj12 said:
If there was a block on a table what would be the normal force between the block and the table. If you could describe the free body diagram that would be great too.
Assuming the ordinary situation, a block resting on a horizontal table, then a free body diagram of the block would show:
- its weight acting down (agent = the earth)
- the normal force acting up (agent = the table)

Since we know the block is in equilibrium, the magnitude of the normal force must equal the block's weight.

So far, none of this has anything to do with Newton's Third law. Did you have a question about it?
 

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