Applications of Circular Motion

Circular motion is not just an abstract physics concept — it governs the motion of satellites, the operation of centrifuges, the design of fairground rides, and much more. In this lesson, we connect the theory to real-world applications.

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Satellites and Orbital Speed

A satellite in a circular orbit has its centripetal force provided by gravity. Setting the gravitational force equal to the centripetal force:

$\frac{GMm}{r^2} = \frac{mv^2}{r}$r2GMm​=rmv2​

Where G is the gravitational constant (6.67 × 10⁻¹¹ N m² kg⁻²), M is the mass of the central body, m is the satellite mass, and r is the orbital radius (measured from the centre of the central body).

Simplifying (the satellite mass cancels):

$v = \sqrt{\frac{GM}{r}}$v=rGM​​

Key insight: orbital speed depends only on the orbital radius and the mass of the central body — not on the satellite's mass. A feather and a bowling ball at the same orbital radius orbit at the same speed.

Worked Example 1

Calculate the orbital speed of the International Space Station (ISS), which orbits at approximately 400 km above Earth's surface. (Mass of Earth = 5.97 × 10²⁴ kg, radius of Earth = 6.37 × 10⁶ m)