TRY IT! Hey, Marshmallow Face! Draw a face on the end of a marshmallow. Place the marshmallow in a glass bottle (the bottle's mouth should be slightly larger than the marshmallow). Wrap clay around a straw about 2.5 cm (1") from one end. Place the short end of the straw in the bottle. Seal the bottle with clay. Stand in front of a mirror so you can see the face on the marshmallow. Suck air out of the bottle. (Make sure there are no leaks!) What happens to the marshmallow? Now stop sucking on the straw. What happens to the marshmallow?
TRY IT! Steel Heat Place a thermometer in a jar and close the lid. Wait five minutes and record the temperature. Remove the thermometer from the bottle. Soak half of a steel wool pad in vinegar for one minute. Squeeze excess vinegar out of the steel wool pad and wrap it around the bulb of the thermometer. Place the thermometer and the steel wool into the jar and close the lid. Wait five minutes. Record the temperature. What happened to the temperature?
TRY IT! Build a Hovercraft Make a hovercraft using cardboard, an empty thread spool, paper, scissors, a pencil, glue, and a balloon. First, cut out a 10-cm (4") square from the cardboard. Next, ask an adult to punch a hole in the cardboard. The hole has to be in the center of the cardboard square and it should be equal to the size of the hole in the spool. Glue the empty spool on top of the hole in the cardboard. Make sure the holes line up. Seal the base of the thread spool using the glue. (This is important so that no air escapes.) Now cover the top of the thread spool by cutting and gluing a circle of paper. Let this dry. Use a pencil to punch a hole in the middle of the paper cover where the hole of the spool is. Blow up the balloon and twist the end. Stretch the mouth of the balloon over the top of the spool. Let the balloon go and give your hovercraft a push. What happens?
TRY IT! It's Your Turn Cut a piece of tissue paper into a 6-cm (about 2") diameter spiral (use the diagram). Cut a piece of thread 15 cm (6") long and tape one end of the piece of thread to the center of the paper spiral. Position a desk lamp so that the light points upward. Ask an adult to hold the paper spiral by the thread about 10 cm (4") above the light. (Caution: Do not allow the paper to touch the light bulb.) What happens?
TRY IT! The Inner Life of a Leaf Fill a bottle with water to within an inch of the top. Take a freshly cut leaf or flower, wrap clay around the stem and place the stem into the bottle. Make sure the clay fits snugly around the mouth of the bottle. Poke a hole through the clay, and insert a straw. Press the clay around the straw and bottle opening so that no air can escape. The straw should not touch the water. Stand in front of a mirror and suck the air out of the bottle with the straw. (This is hard to do if there are any leaks.) What do you observe in the mirror?
TRY IT! Move the Cups Find two disposable cups and some string. Cut the string into two 1'-long pieces. Using tape, attach the end of one piece of string to the bottom of one of the cups, and attach the other end to the edge of a table. Repeat this with the other cup. Position the cups so they hang off the table two inches apart and at the same height. You might need to adjust the spacing between the cups. Blow between the two cups. What happens?
Why are the cups drawn together? Bernoulli's principle states that in areas where air moves rapidly, pressure is low. Blowing between the cups drops the pressure so the higher air pressure of the surrounding air pushes the cups together.
Why did the marshmallow expand? The marshmallow is a spongy solid with air trapped inside the spaces. Sucking air out of the bottle decreases the pressure inside the bottle, which causes the spongy solid-the marshmallow-to expand. Removing the straw from your mouth allows air to rush back into the bottle, increasing the pressure and causing the marshmallow to return to its original size.
Why does air appear at the end of the stem? There are holes in the leaf called stomata and tiny tubes called xylem which run down the stem. The leaf and stem act as a straw for the plant. As you drew air out of the plant, more air was drawn into the bottle through the stomata and xylem. This is the same system that water moves in a plant.
How did you create a hovercraft? The air flowing from the balloon through the holes forms a layer of air between the hovercraft and the table. This reduces the friction. With less friction, your hovercraft scoots across the table.
Why does the paper spiral twirl? The energy from the light heats the air above it. Warm air is lighter than cool air, so as the air heats up, it rises above the lamp. Cool air moves in to replace the warmer, lighter air. This "convection current" causes the spiral to twirl.
Why did the temperature rise? The vinegar removes any protective coating from the steel wool, allowing the iron in the steel to rust. Rusting is a slow combination of iron with oxygen. When this happens, heat energy is released. The heat released by the rusting of the iron causes the mercury in the thermometer to expand and rise.