Why Does a Ball Sink on Water Surface?

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SUMMARY

A ball sinks in water due to the gravitational force (mg) exceeding the buoyant force (Vpg), which is insufficient to keep it afloat. Unlike on solid ground, where the normal reaction force (N=mg) supports the ball, water provides a buoyant force that varies with density. A less dense ball floats, while a denser object, such as a metal ball bearing, sinks. This phenomenon highlights the differences in density and phase between solids and liquids.

PREREQUISITES
  • Understanding of buoyancy and Archimedes' principle
  • Knowledge of density and its impact on floating and sinking
  • Familiarity with the concepts of gravitational force and normal reaction force
  • Basic principles of solid and liquid states of matter
NEXT STEPS
  • Research Archimedes' principle and its applications in fluid mechanics
  • Explore the concept of density and how it affects buoyancy
  • Study the differences between solid and liquid states of matter
  • Investigate surface tension and its role in allowing small insects to walk on water
USEFUL FOR

Students studying physics, educators teaching fluid mechanics, and anyone interested in understanding the principles of buoyancy and density in real-world applications.

Vagrant
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Homework Statement



Why does a ball placed on water surface sink, while one placed on the ground does not



The Attempt at a Solution


I think the ball sinks because mg is more than the upthrust (Vpg), but why doesn't the ball experience normal reaction (N=mg) on the water surface like we do on the ground ?
 
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On water the ball experiences byouncy force. The force isn't great enough to keep the ball above water though. Some bugs also walk on water due to surface intension.
 
I like to think from 2 perspectives - differences in phase and differences in density.For a ball floating on water, there is a difference in density between the ball and the water - the ball is less dense, so it floats! If you use a metal ball bearing, which is denser than water, the metal ball bearing will sink, won't it?

However, on ground, no matter how dense your ball, it won't sink because of the nature of solids.. (revisit your theory of matter, and explain with respect to the particles)
 

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