Calculating Orbital Speeds

Orbital Speed

Orbital Speed

• 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 2πr where r is the radius of a circle 

• The relationship between speed, distance and time is:

$speed = \frac{distance}{time}$

• the average orbital speed of an object can be defined by the equation:

$v = \frac{2\mathrm{\pi }r}{T}$

• Where:

  • v = orbital speed in metres per second (m/s)

  • r = average radius of the orbit in metres (m)

  • T = orbital period in seconds (s)

• This orbital period (or time period) is defined as:

  The time taken for an object to complete one orbit

• The orbital radius r is always taken from the centre of the object being orbited to the object orbiting

Orbital Motion

Orbital radius and orbital speed of a planet moving around a Sun