Perhaps you've seen hot air balloons for sale as science demonstrations/experiments that you fill up with hot air from a hair dryer and let float to the top of the room. This product can be easily recreated on a smaller scale with tissue paper. This project is a great way to demonstrate and learn about gases and density.
You'll need: 5-6 sheets of tissue paper, a strip of paper, a glue stick, a marker, scissors, and a hair dryer.
The first step is to layer 5-6 sheets of tissue paper and fold them in half lengthwise.
Use a marker to draw a half tear drop shape.
Cut along the line and unfold the layers. Each one will be a panel for the hot air balloon.
Using a glue stick, or wet glue thinly applied with a paintbrush, glue one edge (marked in the picture above) and layer another panel on top. Pres down firmly to seal the edge.
Once the glue has dried, unfold the two panels to inspect for any holes. Make sure to seal up any gaps.
Fold enough panels (5 pictured here, but depending on your teardrop shape you may need more or less) to create a round hot air balloon body. Since the seams are facing outward, it is easy to repair any gaps and to fit in the last panel.
Glue a strip of paper inside the opening of the hot air balloon. The paper strip should fit snugly over the hair dryer end you plan on using. This paper strip gives the balloon support and make it easy to inflate.
With the hairdryer on low, fill the balloon with hot air. You will need to use one hand to keep the hot air balloon on the hair dryer, but don't press too tightly. It is necessary that some air escape out the bottom opening rather than creating a hole elsewhere. Once the balloon is filled with hot air, is should rise a little and slowly drift back down to the ground.
The hot air balloon you built out of tissue paper works under the same scientific principle that enables real hot air balloon to fly: warmer air rises in cooler air. It might seem like air is just empty space, but the air around us is a type of matter called a gas. Matter comes in three states: solids, liquids, and gases. Each state is made up of tiny particles called atoms. In a gas, the atoms are spread out and bouncing around constantly. A gas will fill also a container of any size or shape.
Hot air balloons are called so because they are filled with hot air. Real hot air balloons use a flame to heat the air inside, and you used a hair dryer to heat up the air inside the one you built. Gases behave in ways that can be predicted by a set of rules called the ideal gas laws. One of those laws, Charles’s Law, states: V1/T1=V2/T2. This is just a mathematical way of saying that the volume of a gas increases with temperature. Higher temperatures mean more energy, so imagine the air molecules moving faster and spreading out more to take up a larger space. So, when we heat up the air inside, we are increasing the volume. This creates air that is less dense than the cooler air around it. Density is mass per unit volume, so since we have the same amount, or mass, of air, and increase the volume, density decreases.