The Correlation of Pressure and Torque in Rotational Motion

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SUMMARY

The discussion clarifies that pressure does not directly determine the magnitude of torque when using a screwdriver; rather, it is the axial and radial forces that play critical roles. A smooth grip allows for maximum torque based on frictional forces, while varying grip types can introduce tangential components that contribute to torque. Sufficient axial force is necessary to maintain engagement with the screw head, and a tighter grip increases friction, thereby enhancing torque. Ultimately, understanding the relationship between force and torque is essential for effective screwdriver use.

PREREQUISITES
  • Understanding of torque and its relationship to rotational motion
  • Knowledge of frictional forces and their impact on grip
  • Familiarity with the mechanics of hand tools, specifically screwdrivers
  • Basic principles of force, including axial and radial forces
NEXT STEPS
  • Research the mechanics of torque in rotational systems
  • Explore the effects of friction on tool performance
  • Study different screwdriver head profiles and their impact on torque application
  • Learn about grip strength and its influence on tool effectiveness
USEFUL FOR

This discussion is beneficial for mechanical engineers, tool designers, and anyone involved in the practical application of hand tools, particularly those interested in optimizing the use of screwdrivers for various tasks.

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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