A birthday cake candle timer

“Burning candles lose mass”. Use this knowledge to make a timer.

This experiment should take 60 minutes. 

Equipment

• Eye protection
• Pins
• Clamp stand
• Cork
• Heat-resistant mats
• Card or stiff paper
• Wooden splint
• Plasticine or blu-tack to balance the splint
• A timer
• Rule, 30 cm 
• A pencil
• 2 or 3 birthday cake candles (the candles with the spiral markings seem to work better than the plain candles). 

Health, safety and technical notes 

• Read our standard health and safety guidance here.
• Wear eye protection.
• Hot wax can burn, and stain clothes. Wear protective gloves and/or clothing if desired. 
• This is an open-ended problem-solving activity, so the guidance given here is necessarily incomplete.
• If the candle is allowed to burn down too far, it sets light to the splint.
• If the scale is too close to the flame, it too may burn.
• Take care if any nearby activities involve flammable or combustible substances.

Possible approaches

Students make a timer by fixing a birthday cake candle on one end of a splint, pivoted with a pin, in a cork held in a clamp stand. They will need to find a way of making a scale against which the other end of the splint moves.

This scale is then calibrated using a timer. The core of the problem is to get the splint to pivot easily - but not too easily. It is possible to get repeatable results, given care.

 E.g. A birthday cake candle timer -

*the friction between the pin and the wooden splint is important. It can be altered by changing the amount of pressure of the pin against the cork.