Questions

Epiglottis is that prevents food from entering the windpipe. 

It is a cartilageous flap that flaps opens and closes when swallowing. When you swallow, the epiglottis flattens backward to cover the entrance to your larynx and prevent food from entering the lungs and windpipe. The epiglottis returns to its usual position after swallowing.

Effect of adding liquid is to make the cylinder more bottom heavy which is a more stable position

A piano is a musical instrument which has keys, pedals and strings in which the strings are struck by hammers.