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Hands-on science (no lab required).


Would an air-filled balloon have more thrust (force that causes an object to move forward) if its air escapes from a small or a large opening?


* 2 chairs * meter stick * yarn (4.5 meters, or 15 feet) scissors * drinking straw * transparent tape * small balloon * 2 index cards * pencil


1 Form groups of three students.

2 Line up two equal-size chairs 4 m (13 ft) apart with their backs facing each other.

3 Thread a piece of yarn (4.5 m, or 15 ft) through a drinking straw.

4 Tape one end of the yarn to the top of one chair and the other end to the top of the opposite chair so the yarn is taut and level.

5 Slide the straw across the yarn until it is resting next to one chair. This is your starting point.

6 Use a ruler to measure the opening, or nozzle, at the neck of the balloon.

7 In the center of an index card, draw a circle with a diameter (distance across) that is one half that of the balloon's nozzle. Label the card "A." Cut out the circle to make a hole.

8 In the center of a new index card, draw a circle with a diameter that is one half the diameter of the circle on card "A." Label this card "B." Cut out the circle to make a hole.

9 Designate one student and have this student blow up the balloon completely. This balloon is your "rocket." Note: The same student will blow up the balloon each time in future steps.

10 Have a second student use a ruler to measure and record the balloon's approximate length.

11 Have the person who blew up the balloon pinch the balloon's neck, and slip it through the hole in card "A." Continue to pinch the balloon's neck.

12 Hold the balloon under the straw with its nozzle facing the closest chair. Tape the straw to the balloon.

13 Release the balloon.

14 Have a third student observe where the balloon stops. Then, use the meter stick to measure the distance from the balloon's starting point to its stopping point. Record the results.

15 Repeat Steps 9 to 14 two more times.

16 Repeat Steps 9 to 14 three times using card "B."

17 Repeat Steps 9 to 14 three times without a card.

18 For each hole size--"A," "B," and no card--calculate the average distance traveled from your three trials. Record the results.


1. Which balloon setup--"A," "B," or no card--traveled the farthest?

2. Which balloon setup--"A," "B," or no card--had the greatest amount of thrust? Explain.

3. If you were to add a washer to the balloon, would it travel farther than the balloon in the activity? Explain.


1. The balloon setup with no card should have traveled the farthest

2. The balloon setup with no card had the greatest amount of thrust, That's because with a larger opening--in this case, when no card is restricting the nozzle--the air escapes faster than through a smaller opening The quicker the air escapes, the more force it creates to propel the balloon across the string

3. No, it wouldn't travel as far. The washer would make the balloon heavier It would take a greater amount of thrust to propel this heavier balloon to the same distance as the lighter balloon in the activity.
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Title Annotation:air thrust
Publication:Science World
Date:Jan 16, 2006
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