What Causes the Upward Force of Surface Pressure in Water?

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SUMMARY

The upward force of surface pressure in water is quantified by the equation 2 \pi r \gamma_{WG} cos(180 - \theta), which incorporates both buoyancy and surface tension. While water pressure acts perpendicular to the surface, surface tension exerts a tangential force. The balance of these forces explains why a steel blade floats when placed gently on the water's surface but sinks when submerged. Understanding these principles is crucial for comprehending fluid mechanics and the behavior of objects in water.

PREREQUISITES
  • Understanding of buoyancy principles
  • Familiarity with surface tension concepts
  • Basic knowledge of fluid mechanics
  • Mathematical proficiency in trigonometry
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  • Study the principles of buoyancy in fluid dynamics
  • Explore the effects of surface tension on different materials
  • Learn about the mathematical modeling of fluid forces
  • Investigate the behavior of objects at fluid interfaces
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Students of physics, engineers working with fluid systems, and anyone interested in the principles of buoyancy and surface tension in liquids.

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I understand the explanation of tios problem, except the fact that the force acting upwards bacause of surface pressure is 2 \pi r \gamma_{WG} cos(180 - \theta). Why is that?
 
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There is the bouyancy force and the surface tension. The water pressure acts normal to the surface, but surface tension acts tangentially. Weight of course acts downward with gravity, and to balance the forces, on is concerned with the components of pressure and surface tension acting vertically.
 
A steel blade placed gently on the surface of water floats on it. If the same blade is kept well inside the water it sinks. Can you people please explain why? Thanks for the lot of info that you post. It is really of great help.
 

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