Collect three plastic bottles, wash them out and if you wish, remove the labels. Two need to have the same sized opening. Cylindrical bottles work best.

Supplies

1 x 1l bottle

1 x 500ml bottle

1 x any other plastic (PET) bottle

Scissors

Sticky tape

Step 1: Collect Two Plastic Bottles of Different Sizes

The bottles need to have different volumes, you can check this on the label on the back. One being at least double the other is recommended.

Step 2: Remove Labels

Take the two bottles with the same or similar sized openings. Wash them out and remove the labels.

Step 3: Cut Down Third Bottle

Cut the top and bottom off of the third bottle using scissors. Trim it down so it has neat edges.

Step 4: Cut Again

Cut a rectangular piece out of the trimmed down third bottle.

Step 5: Roll

Roll the rectangular piece into a tube the same diameter as the larger bottles opening. Stick tape around the rolled up piece of plastic to secure it.

Step 6: Test It Fits

Test that the tube fits in the opening tightly. If it is a bit loose, add more tape around the outside then try again. Keep repeating this until it has to be pushed in with a little force.

Step 7: Tape to Bottle

Place the tube inside the opening of the larger bottle and secure it with tape. Make sure there are no gaps through which air could escape.

Step 8: Launch!

Put the smaller bottle onto the other end of the pipe then squeeze the larger bottle to fire. If all has been done correctly, the smaller bottle should come flying off.

Step 9: Experiment

What does reducing the volume of the smaller bottle even further do? Try all different sizes and methods of squeezing the bottle to see how it effects the distance travelled.