The Correlation of Pressure and Torque in Rotational Motion

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Discussion Overview

The discussion revolves around the relationship between pressure and torque when using a screwdriver, exploring whether the pressure exerted by the hand influences the torque applied during rotation. The scope includes conceptual reasoning and technical explanations related to mechanics and friction.

Discussion Character

  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants suggest that pressure does not directly determine torque, emphasizing that sufficient grip is necessary to prevent slipping.
  • One participant argues that while pressure can influence the maximum possible torque through friction, the actual grip and its characteristics are more critical.
  • Another viewpoint states that it is force, rather than pressure, that is relevant for the performance of a screwdriver, as pressure is defined as force per unit area.
  • It is noted that the required axial force depends on the torque being applied and the screw head profile, with worn tools requiring more force to achieve the same torque.
  • A summary reiterates that a tighter grip increases friction force, which in turn increases torque, while suggesting that the concept of pressure is not necessary for understanding this relationship.

Areas of Agreement / Disagreement

Participants express differing views on the relevance of pressure in determining torque, with no consensus reached on its significance in practical applications.

Contextual Notes

Participants highlight various assumptions regarding grip characteristics, the definitions of pressure and force, and the conditions under which torque is applied, which remain unresolved.

Robeurer
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TL;DR
Does pressure determine the magnitude of torque?
When you hold a screwdriver with your hand, a pressure is exerted on it. Does the pressure you exert determine the magnitude of torque in rotating the screwdriver?
 
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No, only to the extent that you need to grip the screwdriver hard enough to not slip wheen you turn it.
 
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Robeurer said:
When you hold a screwdriver with your hand, a pressure is exerted on it. Does the pressure you exert determine the magnitude of torque in rotating the screwdriver?
Depends what the grip looks like.

For a smooth solid of revolution grip, the pressure only determines the maximally possible torque, which comes from frictional forces.

But most grips don't look like that, so the local normal forces from pressure do have tangential components which contribute to axial torque.
 
Last edited:
Welcome to PF.

It is force, not pressure, that determines the performance of a screwdriver. Pressure is force per unit area. Area is not relevant to the forces that are applied while using a screwdriver.

You must apply sufficient axial force, to prevent the screwdriver from being rejected by, and disengaging from the screw head. The axial force required, will depend on the torque being applied, and the head profile of the screw. A worn screwdriver will require greater axial force to deliver the same torque.

You must apply sufficient radial grip force, to prevent the handle sliding with friction against your hand. Your grip of the handle limits the torque that can be applied.
 
Robeurer said:
TL;DR Summary: Does pressure determine the magnitude of torque?

When you hold a screwdriver with your hand, a pressure is exerted on it. Does the pressure you exert determine the magnitude of torque in rotating the screwdriver?
The tighter your grip on the handle, the greater the friction force exerted on the handle. The greater the friction force the greater the torque. The concept of pressure is not needed to understand this.
 

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