1. Lighter-Than-Air Flying Devices

2. 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.

3. 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.

4. 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.

5. 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.

7. 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?

8. 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.

9. 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?

10. Test your predictions.
Describe on
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.

12. 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?

13. 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.

14. 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?

15. 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