Create healthy classroom competition with this experiment designed to lift learners, and their scientific curiosity. 

As far as possible, the lifting device is to be constructed from ‘junk’ materials. Your final device must be loaded with chemicals, and be ready to start the experiment when the judges say so.

Suggested timing

An entire morning be devoted to the problem (eg on the last day of term), which would allow 2 hours for practical activities and 30 minutes for judging or the problem be given to the class as a homework exercise 2 weeks or so before the judging.

Judging could then take place in a normal double science lesson, allowing 45 minutes for repair and final adjustments, and 30 minutes for judging.


  • The judges will require a tape measure/metre rule.
  • Identical teaspoons (can be plastic)
  • Sodium hydrogencarbonate (maximum amount = 3 level teaspoons)
  • Citric acid (maximum amount = 9 level teaspoons)
  • Access to water
  • Butter/margarine to reduce friction

Health, safety and technical notes

  • Read our standard health and safety guidance here.
  • Use eye protection.
  • This is an open-ended problem-solving activity, so the guidance given here is necessarily incomplete.
  • Citric acid is an eye irritant. See CLEAPSS Hazcard HC036c.

Possible approach

Perhaps guidance needed for younger age groups to say that water is needed for the reaction. The reaction might be used to do the lifting, or it could be used to start the lifting, eg to trigger movement of a counterbalance. One group solved the problem by using the displacement of water. 

Possibles extension

To increase the chemical content the task could be extended by prior (or subsequent) experimentation, to select the best choice of gases/chemicals.