Students will be amazed by the gravity-defying abilities of water when you show them how the water can remain in a cup even when it is turned upside down. Fill a paper cup to the top with water. Place a piece of poster board over the top of the cup. Hold the poster board in place while you turn the cup upside down. The water will hold tight to the poster board, and the water will be contained. This is because there is more pressure on the outside of the cup than there is on the inside.
There are different types of gases in the air, which can be demonstrated by creating a chemical reaction that releases gas. Fill a water bottle with 1/3 cup of water. Add 1 tablespoon of baking soda and mix. Pour in 1/4 cup of lemon juice, and quickly stretch the opening of the balloon over the bottle opening, making sure it has created a tight seal. The baking soda, a base, will react with the lemon juice, an acid, to create carbon dioxide gas. The carbon dioxide gas will inflate the balloon.
Light is bent when it travels through different types of mediums. This is easily demonstrated by bending a pencil in a glass of water. Fill a glass half way with water and place a pencil into the glass. The top of the pencil will appear disconnected from the bottom because the light is refracting in the water, but not in the air.