# Edexcel IGCSE Physics: Double Science 复习笔记：8.1.4 Orbital Period

### Calculating Orbital Period

• When planets move around the Sun, or a moon moves around a planet, they orbit in circular motion
• This means that in one orbit, a planet travels a distance equal to the circumference of a circle (the shape of the orbit)
• This is equal to 2πwhere r is the radius a circle

• The relationship between speed, distance and time is: