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The Solar System Relative Positions of Earth, Sun, and Planets Gravity on Earth and in Space Weight and Gravitational Attraction Planetary Motion and Gravity
Year 8 • Physics
The Solar System & Gravity
This lesson explores the Solar System, the positions of Earth, the Sun and planets, how gravity works on Earth and in space, and how gravity controls planetary motion.
Lesson Objectives
- Describe the structure of the Solar System.
- Explain the relative positions of the Earth, Sun, and planets.
- Understand gravity on Earth and in space.
- Explain weight and gravitational attraction.
- Understand how gravity controls planetary motion.
1. The Solar System
The Solar System consists of the Sun and all objects that orbit around it due to gravity.
[ Image Placeholder – The Solar System Diagram ]
• The Sun is at the centre
• Planets, moons, asteroids and comets orbit the Sun
• Gravity holds the Solar System together
• Planets, moons, asteroids and comets orbit the Sun
• Gravity holds the Solar System together
2. Relative Positions of Earth, Sun, and Planets
The planets orbit the Sun in fixed paths called orbits.
Earth is the third planet from the Sun.
[ Image Placeholder – Order of Planets from the Sun ]
Closer planets orbit faster than planets farther away.
Curiosity:
Mercury completes a year much faster than Earth because it is closer to the Sun.
3. Gravity on Earth and in Space
Gravity is a force that pulls objects towards each other.
On Earth, gravity pulls objects towards the ground.
[ Image Placeholder – Gravity Acting on Objects ]
• Gravity exists everywhere in space
• Astronauts float because they are in orbit, not because gravity is absent
• Astronauts float because they are in orbit, not because gravity is absent
4. Weight and Gravitational Attraction
Weight is the force of gravity acting on an object.
[ Image Placeholder – Weight on Different Planets ]
• Weight changes on different planets
• Mass stays the same everywhere
• Stronger gravity → greater weight
• Mass stays the same everywhere
• Stronger gravity → greater weight
Example:
You would weigh less on the Moon because its gravity is weaker.
5. Planetary Motion and Gravity
Planets move around the Sun because gravity pulls them inward while their motion carries them forward.
[ Image Placeholder – Planetary Orbits and Gravity ]
• Gravity keeps planets in orbit
• Without gravity, planets would move in straight lines
• Without gravity, planets would move in straight lines
Curiosity:
The Moon stays in orbit around Earth for the same reason.
Practice Questions
A. Fill in the Blanks
- The Sun is at the __________ of the Solar System.
- Planets move in paths called __________.
- Gravity pulls objects __________ each other.
- Weight depends on __________.
- Mass stays the __________ everywhere.
B. True or False
- Earth is the third planet from the Sun.
- There is no gravity in space.
- Weight changes on different planets.
- Gravity keeps planets in orbit.
- Mass and weight are the same.
C. Short Answer
- What is gravity?
- Why do planets orbit the Sun?
- Why do astronauts float in space?
- What is weight?
- What stays constant: mass or weight?
D. Thinking Questions
- Why does the Moon not fall onto Earth?
- Why is gravity stronger on Jupiter than the Moon?
- Why do closer planets move faster?
- Why would life be difficult without gravity?
- Why does throwing an object sideways show orbital motion?
✅ Show Answer Key
A. Fill in the Blanks
- centre
- orbits
- towards
- gravity
- same
B. True or False
- True
- False
- True
- True
- False
C. Short Answer
- A force that attracts objects.
- Because gravity pulls them towards the Sun.
- They are in continuous free fall.
- The force of gravity on an object.
- Mass.
D. Thinking Questions
- It is moving forward while gravity pulls it inward.
- Jupiter has much stronger gravity.
- Stronger gravitational pull near the Sun.
- Objects would float away.
- It curves downward due to gravity.
© Aviate Learning – The Solar System & Gravity (Year 8)
☀️ Interactive Solar System Orbit Simulator
Observe how planets orbit the Sun.
Notice that closer planets move faster while farther planets move slower due to gravity.
Why this happens:
- Gravity pulls planets towards the Sun
- Planets keep moving forward → orbit forms
- Closer planets feel stronger gravity → move faster