Water Fountain 3 (Using Negative Pressure)

Let's take a look!

Watch the video on YouTube.

What kind of experiment is this?

Experimental procedure and explanation:

• Drill a hole in the cap of a PET bottle and insert a straw through it. The duration of the water fountain can be increased using a narrow straw. However, if the straw is too narrow, the energy loss becomes large, leading to a decreased height of the spouting water.
• Insert a small quantity of hot water into the bottle, cap the bottle, and shake well. Be careful not to burn yourself. Next, discard the hot water from the bottle, recap the bottle, turn it upside down, and place it in cold water. A water fountain is then generated.
• By initially filling the bottle with a small amount of hot water and shaking it, water vapor accumulates in the PET bottle. When this water vapor is cooled by the cold water, the water vapor condenses, leading to the decreased volume of water. In addition, the air in the bottle, which expanded due to the heat, contracts. Through these two actions, the pressure inside the PET bottle decreases, resulting in a difference between the internal pressure and the outside atmospheric pressure, and a water fountain is generated. In other words, by lowering the pressure on the exit side, a water fountain is created in the method similar to that of increasing the pressure on the upstream side (Water Fountain 2).
• The second experiment achieves this in a simpler manner. When you squeeze the PET bottle and release it, the bottle attempts to return to its original shape, causing the air inside the bottle to expand and the pressure to decrease. As this occurs, the pressure on the exit side of the straw decreases, and a water fountain is generated.
• These two water fountains were generated by methods that decrease the pressure on the exit side. A pressure lower than atmospheric pressure is referred to as “negative pressure.”

[Keywords]	pressure
[Related items]	Water Fountain 2
[Reference]	“The Wonders of Flow,” Japan Society of Mechanical Engineering, Kodansha Blue Backs, pp.34-37 and 98-101 “Illustrated Fluid Dynamics Trivia,” by Ryozo Ishiwata, Natume Publishing, pp.14-15 and 192-193