| English | Escape velocity |
|---|---|
| Bahasa Melayu | Halaju lepas |
| 中文 | 逃逸速度 |
Definition
The minimum velocity an object needs to completely escape the gravitational pull of a planet or other body.
In exam terms
Escape velocity is the minimum velocity an object must be given at a planet's surface so that it completely escapes the gravitational pull without any further propulsion. It is a speed, measured in m s⁻¹, and it depends on the mass and radius of the planet but not on the mass of the escaping object.
It is found by equating the kinetic energy given to the object with the work needed to move it out of the gravitational field, giving v = √(2GM/r). For the Earth its value is about 1.1 × 10⁴ m s⁻¹, so a rocket must reach this speed to leave without falling back.
Do not confuse it with…
Do not confuse escape velocity with orbital velocity. Orbital velocity keeps a satellite going round in a stable orbit, while escape velocity lets an object leave the field entirely; escape velocity is larger, equal to √2 times the orbital velocity at the same radius.
In Paper 2 this is asked as define escape velocity or explain why escape velocity does not depend on the mass of the object. State that mass cancels because both the kinetic energy supplied and the gravitational work required are proportional to the object's mass, so only the planet's mass and radius matter.
Source: DSKP KSSM Physics Form 4 and 5 (Versi English) (Bahagian Pembangunan Kurikulum (BPK), KPM)