Honolulu (HawaiiNewsNow) - Dr. V and Taizo playing tricks with water with the children at the Shriner's Hospital for Children.
Dr. V Show: Water Bottle Trick
Things you need:
- Clean one liter bottle
- Thumb tack
- Permanent marker
Please perform this and all experiments under the supervision and with the assistance of an adult. Use the tack to poke a hole in the side of the bottle, close to the bottom. Then fill the bottle up with water while covering the hole with your finger. Put the cover on and remove your finger from the hole. What happens? Now unscrew the cap. What happens?
To play a fun trick on someone, use the permanent marker to write, "DO NOT OPEN" on the bottle. Then poke several holes around the side of the bottle and fill the bottle up with water, covering as many holes as possible to keep the water from coming out. Then put the cap on. If this is difficult, try filling up the bottle underwater, and screw the cap back on while the bottle is still underwater. Then leave the bottle on the counter and wait for someone nosy enough to open the bottle and find out what the instructions were for!
How does it work?
Why does the water spew out when the cap is loosened? There are two forces at work in this experiment, gravity and air pressure. Gravity is pushing downward on the water whether the lid's on the bottle or not. Air pressure can't push on the surface of the water when the bottle cap is on, but it is pushing on the outside of the bottle, from all sides. Since the outside atmospheric (air) pressure is greater than the force of gravity, most of the water stays in the bottle. When the lid is uncapped, the air pressure (14.7 pounds per square inch at sea level) AND the force of gravity push down on the water at the same time. This forces the water out of the holes, to the surprise of unknowing bottle-opener.
Could you do this with a larger bottle? A smaller bottle? What difference does it make and why?