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Lesson 1 Grades 6–8

Newton's laws and the balloon rocket

Worksheets (PDF) Open Rocket Builder

On this page
  1. Standards
  2. I can…
  3. Words to know
  4. Materials
  5. Steps
  6. Check for understanding
  7. Teacher notes

Standards

Code In plain words
MS-PS2-2 Plan an investigation showing that a change in motion depends on the total force and the mass.
MS-PS2-1 Use Newton's third law (equal and opposite forces) to explain and design.
6.SP.B.5 (math) Summarize data: mean of repeated trials.

Practice: planning and carrying out investigations. Crosscutting concept: cause and effect.

I can…

Words to know

Materials

Per group: 2–3 long balloons, 5 m of string tied between two chairs, a straw, tape, 10 paper clips, a binder clip, a tape measure, a string to measure the balloon's circumference, worksheet W1.

Steps

  1. 1Hook5 min
  2. 2Teach10 min
  3. 3Investigate30 min
  4. 4Rocket Builder5 min
  5. 5Wrap up5 min
55 minutes · learn plan hands-on wrap up

1Hook5 min

Let go of an untied balloon. What do this, a firework and a space rocket have in common? (They push something out the back and move the other way.)

2Teach10 min

Read aloud

Law 1: objects keep doing what they're doing (still, or moving in a straight line) unless a net force changes it. A rocket sits on the pad until the motor pushes harder than gravity pulls.

Law 2: force = mass × acceleration (F = m × a). The same push gives a light object a big speed-up and a heavy one a small speed-up. That's why rockets are built light.

Law 3: forces come in pairs, equal and opposite. A motor pushes gas out the back; the gas pushes the rocket forward. A rocket doesn't push on the air or the ground, so it works in space.

3Investigate30 min

Balloon rocket on a string, run twice with the same push: alone it goes 4.0 m; with 10 paper clips added it goes only 2.5 m 1 Balloon alone start stopped action: air pushed back reaction: balloon pushed forward 4.0 m 2 Same push, more mass start stopped +10 paper clips action: air pushed back reaction: same push forward 2.5 m more mass, same force: less speed-up, shorter run F = m × a
Same push, more mass: the loaded balloon speeds up less and goes less far.
air rushes outthrustmeasure from the start lineABCDEF
The setup. A string tied tight between two chairs · B straw on the string · C balloon · D tape · E clip holds the air in · F start line.
  1. Thread the straw on the string; tie the string level and tight, at least 4 m long.
  2. Blow a balloon to a measured circumference (e.g. 50 cm). Hold it shut with the binder clip; tape it to the straw.
  3. Release from the start line and measure the distance. 3 trials, same circumference each time.
  4. Tape 5 paper clips to the straw: 3 trials. Then 10: 3 trials.
  5. Find the mean for each mass on W1.

Variable changed: mass. Kept the same: balloon size (push), string, start line.

4Rocket Builder5 min

Open Rocket Builder (Beginner). Follow the tutorial to Build my rocket, then press ▶ Watch it launch. Note three things you see.

5Wrap up5 min

Where is each law in the balloon rocket?

Check for understanding

  1. A rocket pushes gas down; the gas pushes the rocket up. Which law?
  2. Two balloon rockets get the same push. One carries 10 paper clips. Which accelerates more, and why?
  3. True or false: a rocket needs air to push against.
  4. Your trials with 5 clips were 3.2 m, 3.6 m and 3.4 m. What's the mean?
Answer key
  1. The third law.
  2. The one with no clips: the same force on less mass gives more acceleration (second law).
  3. False: it pushes on its own exhaust.
  4. (3.2 + 3.6 + 3.4) ÷ 3 = 3.4 m.

Teacher notes

  • What to expect: more paper clips, shorter distance. If balloons always reach the end, lengthen the string or time the run instead.
  • About MS-PS2-1: the PE is written about collisions. Here students apply the third law to a push-apart interaction (rocket and exhaust); treat it as a partial match and pick up collisions elsewhere if you need the full PE.
  • Extension (F = m × a): a balloon pushes about 0.1 N on a 10 g (0.010 kg) rocket: a = 0.1 ÷ 0.010 = 10 m/s². Add 10 g: 5 m/s². Doubling the mass halves the acceleration. Graph clips vs mean distance.
  • Students under 12: some 6th graders are 11. They do every lesson; the printed rocket's motor flight (Lesson 9) is for 12+, and adults handle all motors. Under-12 students design on screen, track and record.
  • Plan ahead (adult): order the launch pad and controller, wadding and motors now, and look for a field or a local NAR club launch (nar.org). Wait for Lesson 6 to pick the motor class; the common 18 mm (M18) size is a safe bet.
  • Further resources: Apogee Components' free lesson Rockets and the Third Law (apogeerockets.com/downloads/PDFs/58-1.pdf, grades 5–8).

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