This experiment needs to be carried out under adult supervision.
Do not stand over the bottle when pumping it up as it might take off and hit you.
Empty 1.5 litre plastic bottle
Strong cardboard for fins
Cork to fit bottle neck
Bicycle pump with flexible hose
Needle attachment for pump
Please read the safety warning before you start.
Cut 3 right-angle triangles out of cardboard, approx 15cm high and 8cm wide. Tape them to the top of the bottle – this will become the base of your rocket – leaving an overhang of around 3-4cm.
Make a hole right through the cork, just big enough to fit around the bike pump needle.
Fill the bottle half to two-thirds full with water and plug it firmly with the cork.
Put the needle attachment on to the flexible hose of the bike pump and insert into cork.
Stand the bottle upright on its fins and start pumping.
(NB. Older son recommends removing clothes before the final stage!)