....Air Pressure

This is a cool one for air pressure you may have seen. It is an easy one and you probably already have all the materials needed right there with you.

Materials: 
Cup
Water
Note Card

To show air pressure is real and presses in all directions this is perfect. Fill the cup with water, place the note card on top, and turn the cup upside down while placing pressure on the note card with your hand. Once upside down carefully remove your hand from the note card, and the air pressure will keep the card in place to hold the water in the cup. The kids love this and think you are magic. Be careful not to tilt the cup or squeeze or you will release the card and water will go everywhere. I once had to walk around the rest of the afternoon looking like I had peed my pants. The kids will NEVER forget that. It was worth it!