Power of an Object: Desk Force & Newton's Law

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Discussion Overview

The discussion revolves around the application of forces to a desk and the implications of Newton's laws, particularly focusing on the relationship between the force exerted by a hand and the force exerted by the desk. Participants explore scenarios involving static and dynamic forces, the breaking point of the desk, and the theoretical limits of force application.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants assert that if a desk can withstand 50 Newtons, applying a force of 55 Newtons would not be possible without breaking it first.
  • Others argue that if a force of 55 Newtons is applied just before breaking, the desk would exert an equal force back on the hand for that moment.
  • A participant introduces the idea that inertia allows for a brief application of forces greater than the desk's capacity, suggesting that dynamic conditions could lead to different outcomes.
  • Some participants emphasize that in an idealized model, one cannot exert more than the desk's maximum force without it breaking, leading to a scenario where the hand would feel no opposing force once the desk fails.
  • There is a discussion about the difference between static and sudden forces, with some suggesting that Newton's third law applies regardless of the nature of the force.
  • A later reply highlights the distinction between force and power, indicating that they are fundamentally different concepts, though this point remains uncorrected by others.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the application of forces and the behavior of the desk under different conditions. The discussion remains unresolved, with no consensus on the implications of applying forces beyond the desk's capacity.

Contextual Notes

Limitations include assumptions about the nature of forces (static vs. dynamic), the conditions under which the desk breaks, and the lack of clarity on the definitions of force and power as discussed by participants.

Hepic
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Lets say that my desk can stand until 50 Newtons.
So I put my hand up to desk with 20 Newtons,so third Newton's law says that desktop will put force with 20 Newtons my hand. After some seconds,I put force with 50 Newtons,so my hand will feel 50 Newtons too from the desk. After I put force of 55 Newtons(so desk will broke). Theoritically my hand will feel 50,or 55 Newtons ??

Thanks.
 
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Hepic said:
After I put force of 55 Newtons(so desk will broke).
If it breaks at 50N you can't apply 55N to it.
 
Lets say that desktop can stand until 50 Newtons.
Suddenly I put force of 55 Newtons. My hand will feel 50 Newtons or more?
 
How were you able to apply 55 Newtons to a desk that can only withstand 50 Newtons?

The desk always pushes back with a force equal to whatever force you exert on it. So if you managed to push it with 55 N for a moment before it broke, then the desk would have exerted 55 N back on you for that moment.
 
Hepic said:
Suddenly I put force ...
I thought you meant static forces. For a short time you can apply greater forces because of the desks inertia.
 
That depends on the way the desk breaks. You can get a force above 50 N if you accelerate parts of the desk downwards.
Suddenly I put force of 55 Newtons
How do you do that? In general, you can choose the position of your hand, but it is problematic to choose the force in non-static environments (like breaking desks).
 
Hepic said:
Lets say that desktop can stand until 50 Newtons.
Suddenly I put force of 55 Newtons. My hand will feel 50 Newtons or more?

In an idealized model, you won't be able to apply a force of more than 50N. You'll push harder and harder, and the desktop will push back on you with equal and opposite force, until you get up to 50N. When you do, the desktop will break, your hand will go through it and keep moving without anything to oppose it. Imagine that there was a spring scale sitting on the desk, and you're piling weights onto the scale. Every time you add a weight, the reading on the scale goes up. But the moment you get the scale to read 50N, the desk will break, the scale will go into free free on the way to the floor, and it will read zero while it's falling... So you can't apply a force of more than 50N in this idealized model.

It's a different story if you're striking the desk with your fist or a hammer - then we're thinking about accelerating the pieces of the broken desktop, and potentially much larger forces may be involved.
 
Doc Al said:
How were you able to apply 55 Newtons to a desk that can only withstand 50 Newtons?

The desk always pushes back with a force equal to whatever force you exert on it. So if you managed to push it with 55 N for a moment before it broke, then the desk would have exerted 55 N back on you for that moment.

I do not mean about static power,but a sudden one.
So,If I put force 100+ I will feel the same power in my hand?(synchronous)
 
Hepic said:
I do not mean about static power,but a sudden one.
So,If I put force 100+ I will feel the same power in my hand?(synchronous)
Static or sudden doesn't matter: Newton's 3rd law still holds. If you manage to exert a force of X Newtons on the desk, then the desk exerts an equal and opposite force of X Newtons on your hand.
 
  • #10
So does not matter how much force an object can stand.
If I ask an infinite power,I will get the same.(theoritically).
Right?
 
  • #11
Hepic said:
So does not matter how much force an object can stand.
If I ask an infinite power,I will get the same.(theoritically).
Right?
If you can exert the force against the object, then the object will exert the same force against you.

Sometimes it's not so easy to exert that force. Example: It's easy to punch a concrete wall and create a (relatively) large force. Try punching a fly or a piece of tissue paper with that same force. Good luck!
 
  • #12
Hepic said:
So does not matter how much force an object can stand.
If I ask an infinite power,I will get the same.(theoritically).
Right?
No one has corrected this yet, but force and power are two completely different things.
 

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