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.
Kepler's Second Law
formalises Orbits
can be derived from Conservation of Angular Momentum

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