Astound friends with the amazing ability to read a message through two envelopes. Have a friend use a black permanent marker to write a simple one-word message on a white sheet of paper. Have the friend seal the message in a brown envelope to prevent you from seeing. Do not fold the paper that the message is written on. Seal the brown envelope in a second, white envelope. Give everyone present the chance to try to decipher the message. It should be impossible.
Use a four-inch-long tube constructed from rolled up black construction paper to decipher the message. When placed directly against the envelope, the tube will prevent light from reflecting off of the white surface of the envelope. Hold the envelope toward a light source so that light enters from the back. The message should now be clearly visible.
Make a speedboat from a toothpick in a tub of water, with the help of a dab of shampoo. Add a small amount of shampoo to the blunt end of the toothpick before placing it in the water. The toothpick will move forward, with the sharper end leading the way. This is because shampoo reduces the surface tension of liquids, causing the surface tension near the pointed end of the toothpick to pull the toothpick forward.
For a colorful twist, fill a small bowl with milk. Place a bread clip on the surface of the milk and add a drop of shampoo to the hole of the clip. The clip will race around the bowl. Add a drop of food coloring with the shampoo to illustrate the effect in vibrant color.
When milk is used, adding more shampoo will continue to propel the torpedo. Water allows a reaction only once before new water must be used. This is because of the way the molecules of the different liquids interact with the shampoo.
Fill a black trash bag with hot air from a hair dryer. Hold the opening of the bag tightly around the dryer until the bag is full. Then seal the end with tape and attach a long string around the end. Take the bag outside, where the black bag can absorb heat from the sun that will cause the air inside to expand and become lighter. The bag will float because the air inside is less dense than the air outside.