This practical involves students making small rockets out of empty film canisters, decorated with designs of their choosing. The canister is filled with a mixture of baking powder and vinegar, the lid applied and turned upside down. The reaction between the baking powder and vinegar is vigorous and will pop the top off of the canister, making the ‘rocket’ fly upwards.
The film canisters are usually old 35mm types which are getting harder to get hold of nowadays. Photography shops may have used ones they may give you for free or at least know where you could get some.
Students can experiment with various types of propellant. Vinegar and baking powder is the most common, although Alka Seltzer and water or chalk powder and vinegar may be asked for. The reactions will vary in strength so this practical may need to be conducted outdoors.
Equipment required (per set):
Some students may find it difficult to get the cap on in time when the mixtures are added together. Wrapping the Alka Seltzer or baking powder in tissue paper and taping it into the lid acts as a time delay allowing the student to get the cap on, upturn the canister and wait for the rocket to lift off.
- Film canister (pop top ones)
- Baking powder, vinegar, Alka Seltzer, chalk powder, water
- Decorative card/paper/materials
- Sticky tape
- Newspaper (to catch the mess)
- Tissue paper
The decoration of the rocket may make a difference to the trajectory and height the rocket will attain, mainly due to the weight of the finished rocket. Students may want to experiment with fins, nose cones etc.
Some canister lids pop off more easily than others, try to get canisters as similar as possible in order to be fair.
The rockets are powered by compressed gas, namely CO2 which is formed when the baking powder comes into contact with the vinegar (ethanoic acid). Alka Seltzer and similar tablets contain baking powder and dehydrated citric acid, When water is added, the citric acid mixes with the baking powder to produce CO2.
The gas created exerts great pressure on the canister until the lid pops off.