Move an oxo cube at great speed

Make sure you know which side of your table is buttered as you create a slick surface for your swift stock cube.

Timings

It is suggested that either:

An entire morning be devoted to the problem (e.g. on the last day of term), which would allow 2 h 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. 

Equipment

• Items from the junk list to encourage creativity
• The judges will require a stop watch or an arrangement with a computer and photocells if the Oxo cubes move too fast.

Materials per group

• Sodium hydrogencarbonate (maximum amount = 3 level teaspoons)
• citric acid (maximum amount = 9 level teaspoons)
• Access to water
• Butter/margarine to reduce friction

Equipment per group

• Identical teaspoons (can be plastic)
• Safety glasses. 

Health, safety and technical notes

• Read our standard health and safety guidance here. 
• Wear eye protection. 
• This is an open-ended problem-solving activity, so the guidance given here is necessarily incomplete.
• For more information on sodium hydrogencarbonate see CLEAPSS Hazcard HC095a.
• Citric acid is an eye irritant, see CLEAPSS Hazcard HC036c.

Commentary

Some guidance may be needed for younger age groups – e.g. water is needed for the reaction. The reaction might be used to do the moving, or it could be used to start the movement – e.g. to trigger movement of a counterbalance

Extension

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

Notes

This resource is part of a collection of problem-solving activities, designed to engage learners in small group work. Find out how to use these resources, and obtain a list of suggested ‘junk items’ here.