Gravity and Weight

Grade Level

7th Grade Science

Duration

70 minutes

Standards Alignment

This lesson is aligned with the Next Generation Science Standards (NGSS), which complement the Common Core State Standards' emphasis on math skills for science applications:

• MS-PS2-4: Construct and present arguments using evidence to support the claim that gravitational interactions are attractive and depend on the masses of interacting objects.
• CCSS.MATH.CONTENT.7.RP.A.2: Recognize and represent proportional relationships between quantities.
• CCSS.MATH.CONTENT.7.EE.B.4: Use variables to represent quantities and write expressions when solving real-world problems.

---

Learning Objectives (I Can Statements)

• I can explain how the Sun’s gravitational pull affects the motion of the planets.
• I can describe how weight differs across the planets in our solar system due to gravity.
• I can calculate my weight on different planets using proportional relationships.
• I can use mathematical expressions to solve problems involving gravity and weight variations.

Success Criteria

• Accurately describe the role of the Sun’s gravity on planetary orbits.
• Demonstrate understanding of how gravity influences weight on different planets.
• Correctly calculate weight on at least three different planets using given formulas.
• Use reasoning and evidence to explain why weight varies but mass stays the same.

---

Materials

• Whiteboard and markers
• Projector or smartboard
• Printed planet fact cards (gravitational acceleration) for each planet
• Calculators (one per student or pair)
• Handout: “Calculating Weight on Other Planets” worksheet
• Demonstration balls of various sizes and weights (for gravity analogy)
• Chart paper and markers (for group work)

---

Lesson Breakdown

1. Engage: Introduction to Gravity (10 minutes)

• Begin with a brief discussion: What keeps planets in orbit around the Sun?
• Show a simple demonstration using balls and a stretchy fabric (or visual simulation) to represent gravity’s pull.
• Discuss that the Sun’s gravity keeps planets moving in their paths.
• I Can: Explain how gravity affects planetary orbits.

2. Explore: Gravity and Weight Differences (15 minutes)

• Introduce the concept of weight vs. mass. Clarify that mass stays the same, but weight changes depending on gravity.
• Provide planet cards with acceleration due to gravity values (e.g., Earth 9.8 m/s², Mars 3.7 m/s²).
• Discuss how the Sun’s gravity influences orbital paths, but surface gravity determines weight on a planet.
• I Can: Describe how my weight varies on different planets.

3. Explain: Calculating Weight on Other Planets (15 minutes)

• Present the formula for calculating weight on another planet:
  Weight on planet = (Gravity on planet / Gravity on Earth) × Earth weight
• Model a sample calculation using a student’s Earth weight. (For example, a 100 lb person on Mars: (3.7/9.8) × 100 lb = ~37.8 lb)
• Distribute “Calculating Weight on Other Planets” worksheets.
• Students complete calculations for 3-4 planets of their choice.
• I Can: Calculate and compare weights on different planets using a formula.

4. Elaborate: Group Activity – Create a Gravity Chart (15 minutes)

• Divide class into groups of 4-6 students.
• Each group uses their planet cards and calculation worksheets to create a colorful chart/poster showing the weight differences on various planets.
• Groups present their chart briefly to the class, explaining gravity’s effect on weight.
• I Can: Collaborate and communicate scientific knowledge about gravity and weight.

5. Evaluate: Quick Quiz and Reflection (10 minutes)

• Administer a short quiz with 5 questions:
  • Multiple choice on gravity’s role in planets’ motion
  • Calculation question requiring weight on a specific planet
  • Short answer on the difference between mass and weight
• Students write one sentence reflecting on what they learned about gravity and weight.
• Collect quizzes and reflections for assessment.
• I Can: Demonstrate my understanding of the Sun’s gravity and weight differences on planets.

---

Differentiation Strategies

• For diverse learners:

  • Provide calculators and simplified step-by-step formula guides.
  • Use visual aids and analogies for explaining gravity (e.g., rubber sheet model).
  • Pair English Language Learners with bilingual peers for group work.
  • Use graphic organizers to support note-taking.

• For students needing challenge:

  • Offer extension questions involving gravity’s effect on moons or space stations.
  • Have them derive the formula from proportional relationships between gravitational accelerations.
  • Investigate real planetary data to predict astronaut weight changes on long-duration missions.

---

Extension Activities

• Research and create a short presentation about how astronauts’ weightlessness in orbit relates to gravity.
• Calculate how weight changes on dwarf planets or moons like Europa or Titan.
• Use simulation software (if available) to model planetary orbits and surface gravity variations.

---

Closing

• Review key concepts: The Sun’s gravity keeps planets orbiting; surface gravity controls weight differences.
• Reinforce the difference between mass and weight.
• Encourage students to observe gravity’s role in everyday life and space exploration.

---

This detailed, standards-aligned lesson plan includes math integration, hands-on activities, collaboration, and assessment designed for 7th graders to truly understand the Sun’s gravity and planetary weight variations.