Kepler's Second Law
Earth and Space

Kepler's Second Law using a centripetal force kit

Practical Activity for 14-16 PRACTICAL PHYISCS

Class practical

The simple kit demonstrates the increase in speed with a diminishing radius of orbit.

Apparatus and Materials

For each student or group of students

  • Centripetal force kit

Health & Safety and Technical Notes

Ensure that the bungs are securely attached and that each student has sufficient space to whirl the bung safely.

The centripetal forces kit is available from:

Technology Supplies Limited


  1. Set the bung whirling around the top of the apparatus.
  2. Pull on the thread to increase the load.

Teaching Notes

  • Kepler's Second Law states that a planet in its orbit sweeps out equal areas in equal times. The time of orbit of the puck will fall as its radius of orbit decreases.
  • You can measure the load by attaching a newton meter to the bottom of the string. As the force on the puck is increased, its orbit gets smaller and its speed increases.
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