

Gushes from a plastic bottle 


Materials and
mounting
instructions: 

use any plastic bottle; with a hot needle make regular holes at different levels (a) or at the same level (b).

How to play: 

fill the bottle with water, the water will spill out with initial direction perpendicular to the surface and with velocity increasing top down (left bottle). If the cap is closed no water spills out, however one can force it out by squeezing the bottle.

Physics: 


Pascal’s principle: the pressure in a fluid propagates in all directions,

the force due to the pressure is perpendicular to the exit surface,
 the pressure increases with the depth in the water (Stevino’s law),
 if the cap is closed, the water cannot spill out because the volume of the air trapped in the bottle cannot change unless its pressure is changed (Boyle’s law): by squeezing the bottle, the pressure increases and the volume of the air decreases.

Educational
aspects: 


explore the volume of air (Sc)

discover the pressure as a characteristic of interactions in fluids (squeezing  Pa),
 explore Pascal’s principle (more evident with a flasktype bottle  Pa),
 discover Stevino’s law (Pb),
 analyse the relation between pressure and volume of the trapped air (Boyle’s law  Pa),
 explore position and motion energies in water (Ea),
 compare with your expectations.


