Empty a Bottle
Who can empty a full bottle of water the fastest?
Two 1 or 2 Liter Bottles
optional a straw or tube.
To Do and Notice
Fill both bottles with water.
Try to find a way to empty one quickly.
Some things you might try:
Just turn the bottle upside down. Notice that the water drains in fits and starts since air must enter the bottle as the water exits the bottle. This takes a while.
Revolve the bottle in a circle to get the water inside spinning, now invert the bottle. Notice that a spinning vortex forms in the water and the water drains out rapidly.
Insert a straw or tube into the bottle, keep your finger over the end of the straw so it stays full of air. Invert the bottle and let the water run out of the bottle while the air comes in through the straw or tube. What happens?
What's Going On?
The vortex organizes the flow of the water so that an air column runs down the middle of the water. This allows the air to smoothly flow into the bottle as the water exits. The water with the vortex inside drains much faster than the water in the first experiment above.
The straw or tube also provides a one-way path for air to enter the bottle while the water leaves via a different route.
Scientific Explorations with Paul Doherty
26 April 2006