For this simple project on air pressure, you will need a glass of water and two straws. Explore what happens when you try to drink water out of the glass using both straws at once. First, take a sip of water using one straw. The water travels up the straw and into your mouth as usual. Next, put both straws in your mouth, but only one inside the glass. Let the other stay outside the glass. What happens when you try to drink? Does it help to suck harder? Last, place your tongue over the end of the straw going outside the glass. Can you drink water through the other straw now? When you are sucking both straws at once, the lighter air is easily drawn into your mouth instead of the heavier water. Once you exclude the air straw, you are able to reduce the air pressure on the water and draw it upward.
Use soap to break the surface tension of water and race some little cardboard boats. You will need a rectangular cake pan that is 10 inches by 14 inches or larger, an inch of water in the pan, thin cardboard, a pencil, scissors and a bar of soap. Use the pencil to draw three boats on the cardboard. The boats should be about two inches long by one inch wide, pointed at one end and straight across the back end. Cut them out. For each boat, cut a very small triangular shaped notch one-quarter inch long in the center of the back end perpendicular to the edge. Place a small chunk of soap securely inside the notch. Line the boats up at one end of the pan in the water and watch them move forward. The reason they move is because of surface tension. The surface of a liquid is like a stretched rubber sheet--it really wants to shrivel into a smaller shape. The soap breaks the surface tension at the back end of the boat, allowing the tension at the front of the boat to pull it forward. As soon as there is soap all over the surface of the water, the boats will stop moving.
This is an easy project using a hard-boiled egg and white vinegar. Put the egg into an eight-ounce glass jar and pour in about four ounces of white vinegar to cover it. Leave it at room temperature for three days. Remove the egg from the vinegar and dry it. It should feel very different from before. Try bouncing it on the floor like a ball. Did your egg turn to rubber? Not really! Instead, the acetic acid in the vinegar caused the calcium in the eggshell to dissolve into solution. The tough protein membrane just under the shell was left and not effected by the vinegar. Just for fun, try the same experiment with a raw egg, but handle it gently and observe how it looks and feels.