6th Grade Earth Science Lesson
Why Do Outer Planets Move So Slowly? Solar System Scale and Gravitational Motion
Shared by A STEM Educator
6th GradeNGSS Phenomenon-BasedMS-ESS1-2, MS-PS2-445 min
Learning Objective
Students will develop and use scale models to investigate how distance from the Sun affects gravitational attraction and orbital speed, aligned to NGSS MS-ESS1-2 and MS-PS2-4.
Lesson Overview
Students explore the vast, non-uniform scale of the solar system and discover why planets farther from the Sun orbit more slowly, connecting gravitational force to orbital speed through scaled models and ratio analysis.
Materials
- Fruit and sports ball size models: peppercorn (Mercury), grape (Venus/Earth), blueberry (Mars), grapefruit (Jupiter), orange (Saturn), golf ball (Uranus/Neptune)
- Printed Planet Distance Cards (one set per group, see Card Sets)
- Meter sticks or measuring tape (at least 10 m per group)
- Hallway space of at least 15 meters
- Student Investigation Handouts (one per student)
- Calculators
- Colored sticky notes for labeling hallway stations
- Whiteboard or chart paper for class data compilation
- Pencils and colored markers
Scaffolded Task Progression
1Task 1
Warm-Up — Fruit & Ball Size Comparison
Your teacher has placed fruit and sports balls on your table representing planet sizes. Without measuring, rank the objects from smallest to largest and record which planet each represents. Then answer: If the grapefruit (Jupiter) is about 14 cm across and the peppercorn (Mercury) is about 2 mm across, approximately how many Mercurys would fit across Jupiter's diameter?
Your teacher has placed fruit and sports balls on your table representing planet sizes. Without measuring, rank the objects from smallest to largest and record which planet each represents. Then answer: If the grapefruit (Jupiter) is about 14 cm across and the peppercorn (Mercury) is about 2 mm across, approximately how many Mercurys would fit across Jupiter's diameter?
| Object | Planet | Approximate Diameter |
|---|---|---|
| Peppercorn | Mercury | 2 mm |
| Grape | Venus | 12 mm |
| Grape | Earth | 13 mm |
| Blueberry | Mars | 7 mm |
| Grapefruit | Jupiter | 143 mm |
| Orange | Saturn | 120 mm |
| Golf ball | Uranus | 51 mm |
| Golf ball | Neptune | 50 mm |
2Task 2
**Low-Floor Task — Hallway Scale Model of Planet Distances**
Your group will lay out Planet Distance Cards along the hallway using the scale: **1 meter = 1 Astronomical Unit (AU)**.
Using your meter tape, place a sticky note for the Sun at the starting wall. Then measure and place each planet card at the correct distance.
| Planet | Real Distance (AU) | Hallway Distance (m) |
|---|---|---|
| Mercury | 0.39 AU | 0.39 m |
| Venus | 0.72 AU | 0.72 m |
| Earth | 1.00 AU | 1.00 m |
| Mars | 1.52 AU | 1.52 m |
| Jupiter | 5.20 AU | 5.20 m |
| Saturn | 9.58 AU | 9.58 m |
| Uranus | 19.2 AU | 19.2 m |
| Neptune | 30.1 AU | 30.1 m |
After placing all cards: sketch the layout below, then answer — where does most of the 'empty space' in the solar system exist?
```coordgraph
{"title":"Planet Distances from Sun (Scale: 1 unit = 1 AU)","xLabel":"Distance from Sun (AU)","yLabel":"","xRange":[0,32],"yRange":[-1,2],"xStep":5,"yStep":1,"points":[{"x":0,"y":0.5,"label":"Sun"},{"x":0.39,"y":0.5,"label":"Mer"},{"x":0.72,"y":0.5,"label":"Ven"},{"x":1.0,"y":0.5,"label":"Earth"},{"x":1.52,"y":0.5,"label":"Mars"},{"x":5.2,"y":0.5,"label":"Jup"},{"x":9.58,"y":0.5,"label":"Sat"},{"x":19.2,"y":0.5,"label":"Ura"},{"x":30.1,"y":0.5,"label":"Nep"}]}
```
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