Lighter-Than-Air Flying Devices Background • Vehicles designed to travel through air are termed aircraft. • There are two types of aircraft: • 1. those that fly through the air • 2. those that float in air. • Hot air balloons and helium airships float in air. • The density of these aircraft is less than the density of the air itself. • These aircraft which stay afloat by the buoyant force of air, are called lighter-than-air aircraft. • Buoyancy is based on the idea that less dense objects will float in a more dense fluid. • A Styrofoam block, for example will float in water because the Styrofoam is less dense than water. • In the same way, a helium balloon will float in air because helium is less dense than air. • Hot air balloons use propane tanks to heat the air in the envelope, or fabric part, of the balloon. • As this air is heated, it expands and becomes less dense than the surrounding air, allowing the balloon to rise off the ground and floats in the air. • Gas balloons are filled with a low-density gas. • Hydrogen was used in the past in ships such as the Hindenburg. • However, hydrogen easily ignites and was found to be the cause of the tragic explosion of the Hindenburg. • Today helium is used in ships such as the Goodyear blimp. Activity One • • • • What is this object called? How does a hot air balloon move? Does it fly through air or float in the air? What do you think helps the balloon to float in the air? • What is the envelope, or fabric part, of the balloon filled with? • What do you know about hot air? • Propane tanks are used to heat the air in the balloon. • When this air is heated, it expands and becomes less dense, or “lighter,” than the air around the balloon. • This allows the balloon to float. • Warm air expands and becomes less dense. • Hang two paper bags upside down and have a light source placed beneath one bag. • Observe what happens. • What do you think will happen when the light is turned on? • Where will the heat come from? • Where will the heat go? • What do you think will happen to the bag? • Test your predictions. • Describe on 2.3.3. • The air in the bag with the lamp under it will warm from the heat of the light bulb. • As it warms, the air expands, becoming less dense than the air surrounding it and the air in the other bag. • As a result, this end of the balance scale will rise as the bag begins to float. Activity two • • • • What is this object called? How does it move? Does it fly through air or float in air? What do you think helps the blimp to float in air? • What is the blimp filled with? • What do you know about helium? Helium • Helium Balloon-Helium is less dense that air therefore it floats. • Lighter than air aircraft have special controls to manage their motion through air. • They are able to float at different altitudes depending on how the pilot controls the density of the aircraft. • What would happen if I let go of the helium balloon? • How high do you think it would travel? • Will it move to the ceiling of the classroom? • Of we were outside, would it travel farther up in the sky? • How could you control the balloon so that it did not float all the way to the ceiling? • Challenge- Experiment with the balloon to see if you can control it? • Activity sheet -2.3.4.