# Normal reaction

1. Mar 22, 2007

### Vagrant

1. The problem statement, all variables and given/known data

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

3. 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 ?

2. Mar 22, 2007

### Kanse

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.

3. Mar 22, 2007

### saplingg

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)