Is the weight of an object exerted on another object?

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Discussion Overview

The discussion revolves around the concept of force exerted by an object resting on another object, specifically focusing on whether a book resting on a table exerts its weight on the table. Participants explore the implications of gravitational force and Newton's Third Law in this context.

Discussion Character

  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants express confusion about why a book resting on a table exerts a force equal to its weight on the table, questioning the relationship between gravitational force and the force exerted on the table.
  • One participant suggests that if an external force is applied to the book, such as pushing it down, the total force exerted on the table would increase, illustrating the cumulative effect of forces acting on the book.
  • Another participant emphasizes that the table exerts an equal and opposite force on the book, in accordance with Newton's Third Law, which helps explain why the book exerts a downward force on the table.
  • Some participants provide examples of heavy objects causing tables to bend or break, reinforcing the idea that objects exert forces downwards due to gravity.

Areas of Agreement / Disagreement

Participants generally agree on the application of Newton's Third Law and the concept of forces acting on the table, but there remains some confusion and debate regarding the initial understanding of how these forces interact.

Contextual Notes

Some statements reflect assumptions about gravitational force and the nature of contact forces that may not be universally accepted or fully explained within the discussion.

Krishna24
I have read on the internet that if an object rests on a table, that object will exert the force of its weight on the table. But, for some reason, that doesn't make sense to me. If I have a 10 kg book that rests on a table, the gravitational force on that object will be 98 N. If gravity is exerting a force on the book, why would the book be exerting a force of 98 N on the table?
 
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Krishna24 said:
I have read on the internet that if an object rests on a table, that object will exert the force of its weight on the table. But, for some reason, that doesn't make sense to me. If I have a 10 kg book that rests on a table, the gravitational force on that object will be 98 N. If gravity is exerting a force on the book, why would the book be exerting a force of 98 N on the table?
What do you think is holding the book up? Why does it not just fall to the center of the Earth?
 
If you put your hand on the book and push with a force of 100 N, you exert a force on the book, just like gravity does. What is the force «felt» by the table now? It would be 198 N, i.e the combination of the forces exerted by both you and gravity.

From the point of view of the table, it is the book that pushes on it. The table doesn't «see» the hand or the gravity pushing on the book.
 
Krishna24 said:
why would the book be exerting a [downwards] force of 98 N on the table?
Because (a) the table is exerting an upwards force of 98N on the book, and (b) Newton's Third Law.
 
When you put something really, really heavy on a table, the table bends until it snaps. That's because the object, which is trying to get to the ground, is exerting a force on the table. It's the same as if the object is placed on the ground; it's still trying to go downwards and so it is exerting a force on the ground, and the ground is exerting an equal and opposite force on it, keeping it from just falling through the ground.
 
A Lazy Shisno said:
When you put something really, really heavy on a table, the table bends until it snaps. That's because the object, which is trying to get to the ground, is exerting a force on the table. It's the same as if the object is placed on the ground; it's still trying to go downwards and so it is exerting a force on the ground, and the ground is exerting an equal and opposite force on it, keeping it from just falling through the ground.
A Lazy Shisno said:
When you put something really, really heavy on a table, the table bends until it snaps. That's because the object, which is trying to get to the ground, is exerting a force on the table. It's the same as if the object is placed on the ground; it's still trying to go downwards and so it is exerting a force on the ground, and the ground is exerting an equal and opposite force on it, keeping it from just falling through the ground.

Thank you so much. I understand it now.
 
jtbell said:
Because (a) the table is exerting an upwards force of 98N on the book, and (b) Newton's Third Law.
Thank you very much for you reply. I understand it now
 

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