But It's Full...

Fill a cup with water.  All the way.  So you can't put another drop in the cup without some spilling out.

How many pennies do you think you can add to the cup before water will spill out? 

One?  Maybe two?

Give it a try....

Once again, we see evidence of water sticking to itself (cohesion) to form a strong surface.

Try again with a drop of soap mixed in with your water...