Gravitation – Complete Intermediate Notes
Stage 1 • Page 8 • Geostationary & Polar Satellites
1. Artificial Satellites
An artificial satellite is a man-made object placed in orbit around the Earth for scientific, communication, or navigation purposes.
- Revolves under Earth’s gravitational force
- Follows circular or elliptical orbits
- Energy and motion depend on orbit radius
2. Geostationary Satellite
A geostationary satellite is a satellite that appears stationary with respect to an observer on Earth.
Conditions for Geostationary Orbit:
- Orbital period = 24 hours
- Orbit must be circular
- Orbit must lie in Earth’s equatorial plane
- Direction of revolution same as Earth’s rotation (west to east)
Important:
If any one condition is violated, satellite will not be geostationary.
3. Height of a Geostationary Satellite
Using time period formula:
T = 2π √(r³ / GM)
For geostationary satellite:
r ≈ 4.23 × 10⁷ m
Height above Earth’s surface:
h ≈ 3.6 × 10⁷ m (≈ 36,000 km)
Exam Tip:
This value is often directly used in numerical problems.
4. Uses of Geostationary Satellites
- Television broadcasting
- Satellite communication
- Weather forecasting
- Telecommunication networks
5. Polar Satellites
A polar satellite revolves around Earth in a plane that passes near the poles.
- Orbit inclined nearly 90° to equator
- Low altitude orbit
- Covers entire Earth due to Earth’s rotation
Key Feature:
Polar satellites provide global coverage.
6. Uses of Polar Satellites
- Remote sensing
- Weather monitoring
- Earth mapping
- Environmental studies
- Military surveillance
7. Comparison: Geostationary vs Polar Satellite
| Geostationary | Polar |
|---|---|
| Appears stationary | Moves relative to Earth |
| High altitude | Low altitude |
| Equatorial orbit | Polar orbit |
8. Common Mistakes to Avoid
- Assuming polar satellite is stationary
- Wrong height of geostationary orbit
- Forgetting equatorial condition
- Confusing uses of both satellites
Stage 1 • Page 8 Completed Successfully ✅
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