Centripetal Force (Oxford AQA IGCSE Combined Science Double Award)

Centripetal Force

• A less massive body or object will orbit a more massive body or object

  • For example:

    • A planet orbiting a Sun

    • A satellite orbiting the Earth

• For any object to be in orbit, there must be a force pulling the object toward the centre of the orbit

• This force is called the centripetal force

  • For an object in space, the centripetal force is gravity

• The gravitational force exerted by the more massive body on the orbiting object is always attractive

  • Therefore, the gravitational force always acts towards the centre of the larger body

• The gravitational force will cause the body to move in a circular path

• So the gravitational force acts at right angles to the direction of motion

The gravitational attraction of the moon orbiting the Earth

Centripetal Acceleration

Extension Tier only

• The force of gravity always acts towards the centre of the orbit

• This is an unbalanced force and therefore causes acceleration towards the centre of the orbit

  • Constantly changing the direction of motion of the body and therefore its velocity

• Velocity is a vector quantity

  • Equal to speed in a given direction

• The speed of the object moving in a circle is constant because it is travelling the same distance every second

  • This means that an object moving in circular motion travels at a constant speed but has a changing velocity

• An object that has a constantly changing velocity therefore has acceleration

Orbit of the International Space Station (ISS)