Motion and Orbits
Newton’s Laws of Motion:
- N1: Inertia
- A body in straight line motion (or rest) continues unless an external force acts on it.
- N2: Acceleration (change of velocity with time)
- depends on force F applied and mass m of object
- a = F/m, or, equivalently, F = ma
- N3: action = -reaction,
- action = force on object 1 from object 2 = F1ɚ
- reaction = force on object 2 from object 1 = F2ə
- i.e. F1ɚ = - F2ə
Imply a certain, definite, force must be present to explain planetary orbits
- For the moon, the acceleration, hence Force per unit mass, was 1/3600 the acceleration of gravity at the Earth’s surface
- Motion in a circle of radius r at velocity v requires a radial acceleration of v2/r