How to make a very simple bottle rocket with household items. No construction required!

This was adapted for use at Wood Hatton Playcentre, an early childhood education centre in Wainuiomata, New Zealand.

you will need:

1 plastic bottle with a sipper top. 400 ml to 750 ml work well, I have not successfully launched anything larger than 750 ml
Baking Soda
Citric acid
Paper square, a bit bigger than a memo cube is good. About 13-15 cm is good. The bit in the photo is too big.
Spoon and bowl for mixing
Water

and a bowl of water for testing the rocket powder :-)

Step 1: Make the Rocket Powder

Mix together roughly equal amounts of citric acid and baking soda in a dry bowl. The kids will have fun doing making their own rocket powder. Test a little powder by dropping some into a bowl of water. It should fizz up immediately. This is a lot of fun and you should expect the kids to spend a lot of time experimenting with the powder, it can get very messy.

Step 2: Wrap the Charge

Put some powder into the middle of the piece of paper. You want as much as you can but still be able to fold it up nicely. About 1 1/2 T works well for a 400 ml bottle.

The purpose of the paper is to stop the powder from getting wet just long enough for you to put the lid on. It doesn't need to be perfect.

I have found that standard photo copy paper (80 gsm) works really well.

Step 3: Put It All Together

Fill the bottle about way 1/3 with water. The amount will depend of the size of the bottle. You need an air gap to build up pressure. Don't use too much water or the rocket will be too heavy to lift off.

Put the charge into the bottle. If you can, avoid getting it wet. Make sure the sipper lid is CLOSED and screw the lid on tightly.

Give it a shake and put it upside down in the can. Tilt the bottle direction you want the rocket to go. Wait.

Step 4: Launch

The pressure will build up until it pops the sipper open and the rocket launches.

If it stops fizzing and the rocket still hasn't launched you can carefully pick it up and pop the sipper by hand, it may still launch into the air.

You can re-use the bottle indefinitely by emptying it and removing the left over paper.