How can you hide a message underwater without getting it wet?
Equipment: glass container with lid, glass, double-sided tape, message.
Fill a glass tank approximately halfway full with water. Tape a message to the bottom of a glass and fix the bottom of the glass to the inner side of the lid of the glass tank using double-sided tape. Gently close the lid, immersing the glass, upside down, in the water. When you open the lid and retrieve the glass from the water, you’ll see that the message inside is still dry! You can prove the presence of air in the glass by covering a candle with the glass and repeating the process - the candle will continue to burn, despite the fact that the liquid level outside the glass is higher than the flame.
When the glass is immersed in water, it contains air. Water tends to push light air upward, compressing it and trapping it inside the glass, which prevents the water itself from rising to fill the glass. Your message is safely hidden inside this air pocket!
Many more cool experiments await you in the MEL Physics subscription!
Warning! Only under adult supervision.