IB MYP 4-5 Physics- The solar system , Planets and Satellites- Study Notes - New Syllabus
IB MYP 4-5 Physics-The solar system , Planets and Satellites- Study Notes
Key Concepts
- The solar system , Planets and Satellites
The Solar System
The Solar System
The solar system consists of the Sun, eight planets, their moons (satellites), dwarf planets, asteroids, comets, and meteoroids.
- The Sun is the central star; its gravity holds the entire solar system together.
- Planets and satellites follow elliptical orbits due to the gravitational force of attraction.
Planets
There are eight planets in the solar system, divided into two groups:
Inner planets (terrestrial planets): Mercury, Venus, Earth, Mars
- Small, rocky, dense.
- Closer to the Sun, with shorter orbits (years).
Outer planets (gas giants): Jupiter, Saturn, Uranus, Neptune
- Large, mostly made of hydrogen and helium.
- Have rings and many moons.
- Longer orbital periods (years).
Planetary Motion:
- Planets orbit the Sun due to gravity.
- They rotate about their own axes (giving day and night).
- The time taken to complete one orbit defines a planet’s year.
Satellites
A satellite is any object that orbits a planet.
- Natural satellites: e.g., Earth’s Moon.
- Artificial satellites: man-made objects launched into orbit for specific purposes.
Uses of artificial satellites:
- Communication (TV, internet, phones).
- Navigation (GPS systems).
- Weather forecasting (meteorological satellites).
- Earth observation and research.
- Military and surveillance purposes.
Satellite Orbits:
- Geostationary orbit: Satellite appears fixed above one point on Earth; period = 24 hours; used for communication and weather monitoring.
- Low Earth orbit: Closer to Earth, shorter orbital periods (~90 min); used for imaging and GPS.
Key Notes
- Gravity is the force that keeps planets in orbit around the Sun and satellites in orbit around planets.
- Orbital speed depends on distance from the central body (Kepler’s Laws).
- Artificial satellites must move at a specific speed to remain in orbit—too slow and they fall back, too fast and they escape.
Example:
Explain why the planets in the solar system orbit the Sun rather than flying off into space.
▶️ Answer/Explanation
The Sun has a very large mass, which creates a strong gravitational pull.
This gravitational force acts as the centripetal force that keeps the planets moving in nearly circular orbits.
Without this force, the planets would continue moving in straight lines and drift into space.
Example:
Jupiter takes about 12 years to orbit the Sun, while Earth takes 1 year. Explain why Jupiter’s orbital period is longer than Earth’s.
▶️ Answer/Explanation
Jupiter is much farther from the Sun than Earth.
The gravitational pull of the Sun is weaker at that distance, so Jupiter moves slower in its orbit.
Since its orbital path is also much larger, it takes more time to complete one revolution.
Example:
The Moon takes about 27 days to orbit Earth. Explain why the Moon does not fall down to Earth despite the gravitational attraction.
▶️ Answer/Explanation
Earth’s gravity pulls the Moon toward it, but the Moon also has forward motion (tangential velocity).
Instead of falling straight down, this motion makes the Moon constantly “fall around” Earth.
This balance between gravity and forward motion keeps the Moon in orbit.
Example:
A geostationary satellite orbits Earth once every 24 hours. Explain why this orbit is especially useful for communication satellites.
▶️ Answer/Explanation
A geostationary satellite remains above the same point on Earth because its orbital period matches Earth’s rotation period.
This makes it ideal for communication, as ground antennas can stay fixed in one direction without needing to track the satellite.
It provides continuous coverage of the same region on Earth, making it useful for TV, internet, and weather monitoring.