Double-Barreled Rocket

Purpose: The purpose of this activity is to build a simple rocket and put Newton's third law (For every action there is an equal and opposite reaction) to the test.

Materials

• plastic soft drink bottle
• four drinking straws (two different sizes and thicknesses)
• modeling clay
• construction paper
• science journal

Procedure

1. Check the bottle for any cracks or damage. The bottle must be damage free!
2. Take off the soft drink label and place it in the trash.
3. Place a ball of modeling clay around one end of the smaller straw. Do not poke the straw through the clay! The ball of modeling clay needs to be large enough to cover the mouth of the bottle.
4. Place the end of the smaller straw that has clay on it inside the mouth of the bottle to seal the mouth of the bottle.
5. Test for leaks by plugging the other end of the small straw with your finger and squeeze the bottle. The bottle should feel hard when there are no leaks. Be sure not to squeeze with crushing force!
6. Cut two strips of construction paper the length of the 22 cm by 28 cm paper; then cut each strip so that it is 2 cm thick.
7. Measure the length of one piece to be 14 cm and cut it; then measure the length of the second piece to be 7 cm and cut it.
8. Bend the two pieces of construction paper strips to form circles and tape eac one, joining either end of the paper.
9. Place the 14-cm strip of construction paper on the base of the larger straw so that it looks like it forms a hoop around the straw.
10. Do the same with the 7-cm strip of construction paper at the end of the large straw, forming a hoop.
11. Place a small ball of clay into the end of the large straw like a cork.
12. Place the larger straw over the smaller one and hold the paper loops on the top side of the bottle rocket with another straw so that the paper loops rest on the straw for stability.
13. Give the bottle a quick squeeze and make observations.
14. Record your observations in the science journal.

Conclusion

1. What made the straw rocket move forward?
2. Why does the smaller straw have to fit tightly in the bottle?
3. What is the function (job) of the two loops of construction paper?

What's Happening?
Newton's third law states: For every action there is an equal and opposite reaction. The action is the air shooting out of the end of the larger straw (rocket), and the reaction is the forward movement of the rocket. By squeezing the plastic bottle, the air inside the bottle is blown through the smaller straw and into the larger straw (rocket). Since the front end of the larger straw is plugged, high pressure builds up in the larger straw and makes it shoot forward.

---

Answer Key

1. What made the straw rocket move forward?

The straw rocket moved forward because of Newton's third law: For every action there is an equal and opposite reaction. The action is the air shooting out of the end of the larger straw (rocket), and the reaction is the forward movement of the rocket.

2. Why does the smaller straw have to fit tightly in the bottle?

The smaller straw must fit tightly in the bottle so that the air pressure will build up in the larger straw and launch the rocket.

3. What is the function (job) of the two loops of construction paper?

The two loops of construction paper act as wings that funnel the air through the loops to provide lift.