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### Force, Motion, and Energy: Build a Blimp

#### by Girlstart

Build a blimp and become an aerospace engineer! In this hands-on activity, kids explore the physics of force by creating balloon blimps with a propulsion system. They problem solve how to make their blimp buoyant while being propelled forward. The Girlstart girls enjoyed testing different amounts of weight added to their blimps to make them buoyant and propel specific distances.

Overview:
Students compare and explain forces that act on air-filled and helium balloons. Students use both types of balloons to create a blimp that is neutrally buoyant and then modify their design with a propulsion system that will propel their blimp forward.

Objectives:

 (4.5A) Measure, compare, and contrast physical properties of matter, including size, mass, volume, states (solid, liquid, gas), temperature, magnetism, and the ability to sink or float (5.6D) Design an experiment that tests the effect of force on an object. (4.6D) Design an experiment to test the effect of force on an object such as a push or a pull, gravity, friction, or magnetism.

Materials:

• Aeronautic Engineer poster
• Pre-measured weights of paper clips

For each group (2-3 students)

• 2 9in balloons filled with helium
• Clear tape
• Duct tape
• Straws (not flexible)
• Large paper clips
• Small paper clips
• White copy paper
• Meter stick or tape.

For each student

Vocabulary

 buoyancy the ability of matter to float in a liquid or gas force a push or pull gravity A force that pulls all objects toward each other hover to remain floating or suspended in the air mass the amount of matter in an object motion a change of position neutral buoyancy condition in which an object’s mass equals the mass it displaces in its surround medium; the object will neither sink nor rise propel to cause to move forward; to launch with great force propulsion the process of causing something to move by applying a force against it.

Preparation:

• Conduct the activities prior to teaching the lesson. The blimp is constructed using two 9in balloons because one balloon will not float once the propulsion system is attached.
• Using Helium tank, per-fill 2 balloons/group before club.
• Students may inflate balloons by blowing into the straws, but they will need to switch out straws so that each student has their own to blow into.
• Make copies of Build a Blimp Results page.
• Make copies of Parts of a Blimp diagram.

Careers
Aerospace engineers create machines, from airplanes to spacecraft. They design, develop, and test aircraft, spacecraft, and missiles and supervise the manufacture of these products. Aerospace engineers who work with aircraft are called aeronautical engineers.

Engage:

1. Hold up two balloons – one filled with air and one filled with helium. Let both balloons go. Ask students to explain the difference between the balloons. Answers might include - the balloon that floats is filled with helium gas. The balloon that sinks is filled with air.
2. Ask students if they think it is possible to design a system to make the balloons travel across the room instead of up or down. Ask and discuss:
• What special type of balloon can move horizontally? A blimp moves forward over the ground. The Goodyear blimp is a great example. They can be seen flying above stadiums during football games. Students will look at a diagram of a blimp later in the lesson.
• What are blimps used for? Blimps used to be used for military purposes. Today blimps are used for advertising, TV coverage, and tourism.
1. Before students begin brainstorming ways to make the balloons change direction they will need to understand how the two different balloons work. Ask and discuss:
• What force causes the air-filled balloon to sink? Gravity pulls on both balloons, but since the balloon filled with air is heavier than air by itself, it sinks to the ground.
• Why does the balloon filled with helium float? The helium gas is lighter than air.
• What other forces can cause a balloon to change its motion? Blowing wind and hitting a balloon can cause it to change motion.
• What would happen to the helium balloon if we went outside and released it? Students may share personal experiences of watching balloons float upward until gone from view. See background information for an example of a helium balloon that reaches the top of the atmosphere.
• How is the air like water? If you put an object such as a baseball in a pool, the ball will sink. If you put an empty bottle in a pool, the bottle will float at the top because the air filled bottle is lighter than the water. Compare the helium balloon to the bottle in the pool. The balloon will float toward the top of the atmosphere like the bottle will float to the top of the water.

Explore:

1. Introduce the challenge. Students will create a blimp that will travel forward across the room while displaying an advertisement. Students will need to control the forces acting on the blimp so that it will move forward.
2. Organize students into groups of two or three. Give each group two Mylar balloons, straws and clear tape. Ask and discuss:
• How can you connect the balloons so they move as one system? The lesson shows how to connect the balloons using one straw, but students may have other ideas they would like to try. Students must be careful not to add too much mass to the system. Otherwise the blimp will start to sink.
• How can you get the balloons to hover? Using the directions below, students will find that the blimp will still rise upward. They many suggest adding mass to help the balloon float in the air.
1. Groups follow their plan or the plan outlined below to connect their balloons and make the blimp hover.

Explain:

1. Groups demonstrate their hovering blimps. Create a table on the board to record the mass required for each blimp to hover in the air.
• Why is the balloon able to float? Adding mass to the balloon makes it heavier. This allows gravity to pull the balloon toward the ground. Explain that the balloon is still buoyant, but it becomes neutrally buoyant when it neither sinks nor rises upward.
• What forces are being applied to the balloon? Gravity is pulling down on the balloon. The items attached to the balloon help to weigh it down.
• What propels a blimp? Give each students a Parts of a Blimp diagram. Read the article and discuss how the parts work together to provide thrust and lift for the blimp.
• What force could we apply to the balloon to make it move across the room? Students will explain that by filling the latex balloon with air and then letting go of the straw, the force of the air leaving the propulsion system will push the blimp forward. On the board, draw a diagram showing the force of air moving in one direction, and the motion of the blimp in the opposite direction.
1. Ask each group to inflate their balloons by blowing into the straw or using a balloon pump. Ask,
• When we let go of the straw, what should happen? Air will move out of the balloon and out through the straw. This force of air will push the balloon forward.
1. Ask each group to inflate their propulsion systems and then release them. Students discuss their results.
• Which way did the blimp travel? Why? Students explain the motion their blimp made. Many students will observe their balloons moving in a circular motion. Some balloons may move lower to the ground.
• What did the blimp do that you did not expect? Answers might include: The air we pushed into the balloon weighed the blimp down, making it sink to the floor.
• What might you want to change about the design so that it will travel in a straight line without sinking? Students will recognize that they need to remove some of the weight they added earlier so that the blimp will not sink after being released. Students may also suggest altering the design to make the blimp move in the desired direction.

Elaborate:

1. Remind students that their challenge is to control the forces acting on the blimp so that it can travel across the floor while displaying an advertisement.
2. Ask students to discuss in their groups the modifications they will need to make so their blimp will travel across the room to their partner. Students may refer the Parts of Blimp diagram for ideas. Students’ ideas may include:
• Adding tail fins: rudders and elevators
• Changing the position of the balloons
• Making a new connection between the balloons
1. Create a class list of modifications students may make based on each group’s discussion.
2. Students may cut fins, rudders, or other pieces out of white copy paper to help direct the blimp as it moves forward. Students need to keep in mind that any changes they make will affect the overall weight of the blimp. They must be sure not to weigh it down to the ground or let it float up to the ceiling.
2. Students test their blimp and make adjustments based on their results.

Evaluate:

1. Each group describes their design and demonstrates their blimp. Ask and discuss:
• How well did your propulsion system work? Did you have to make any changes? Answers will be based on results.
• How did you modify your blimp so that it could fly straight? Answers will be based on results.
• What would you still like to change in your design? Why? Answers will be based on results.
1. Students complete reflections in their Engineer’s Journal.
2. If time permits, ask students to consider what would happen if they connected all of the balloons. How much mass would they need to add to the super blimp to make it hover above the ground?

Resources:
How helium balloons work
http://science.howstuffworks.com/helium2.htm

Background Information:

Helium balloons work because of buoyancy. Buoyancy is the ability of matter to float in a liquid or gas. Helium is a lot lighter than air, so a helium balloon that you hold by a string is floating in a "pool" of air and displacing an amount of air. As long as the helium plus the balloon is lighter than the air it displaces, the balloon will float. Helium weighs 0.1785 grams per liter. Nitrogen weighs 1.2506 grams per liter, and since nitrogen makes up about 80 percent of the air we breathe, 1.25 grams is a good approximation for the weight of a liter of air. A balloon that is one foot (30 centimeters) in diameter holds about half a cubic foot of helium, which is the same as 14 liters. This means the balloon will weigh about half an ounce (14 grams) less than the same sized balloon filled with air.

Because of its buoyancy the helium balloon floats upward. Blimps and balloons are generally quite large because they have to displace a lot of air to float.

If students are curious about how high a helium balloon will float in the air, here is an interesting experiment that films a helium balloon traveling to the top of the atmosphere before popping. http://blogs.howstuffworks.com/2010/10/22/when-i-let-a-balloon-go-how-high-can-it-go/

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Girlstart is an award-winning Austin-based non-profit organization dedicated to empowering girls in science, technology, engineering, and math (STEM).

The views expressed are those of the author and are not necessarily those of Science Friday.