| English | Orbital velocity |
|---|---|
| Bahasa Melayu | Halaju orbit |
| 中文 | 轨道速度 |
Definition
The velocity a satellite must have to stay in a stable orbit at a given radius, where gravitational force provides the centripetal force.
In exam terms
Orbital velocity is the velocity a satellite must have at a given radius to stay in a stable circular orbit, where the gravitational force provides exactly the centripetal force needed. It is measured in m s⁻¹ and depends on the mass of the central body and the orbital radius, not on the satellite's mass.
Setting gravitational force equal to centripetal force, GMm/r² = mv²/r, gives v = √(GM/r). This shows that a satellite in a lower orbit (smaller r) must move faster.
For example, a low-orbit satellite around the Earth travels at roughly 8 × 10³ m s⁻¹.
Do not confuse it with…
Do not confuse orbital velocity with escape velocity. Orbital velocity keeps a satellite circling at a fixed radius, while escape velocity is the larger speed needed to leave the field completely (escape velocity = √2 × orbital velocity at the same radius).
In Paper 2 this is asked as derive an expression for orbital velocity or explain why a satellite in a lower orbit moves faster. Show that equating GMm/r² with mv²/r cancels the satellite's mass m, leaving v = √(GM/r), so a smaller radius gives a larger speed.
Source: DSKP KSSM Physics Form 4 and 5 (Versi English) (Bahagian Pembangunan Kurikulum (BPK), KPM)