This project requires the assistance of an adult.
You will need an empty bottle, 2 balloons, tape, a rubber band, and a blade or scissors (that must be handled only by an adult).
First, ask an adult to make a rectangular slit at the centre of the bottle cap using the blade.
Then cut one balloon to obtain a rectangular piece that is slightly larger than the slit on the cap.
Place the rectangular balloon piece over the slit (on the exterior side of the cap) and use the tape to seal 3 sides of the balloon onto the slit, leaving only one side of the balloon piece open.
Now, cut a circle (about 1 centimetre in diameter) on the body of the empty bottle.
Attach the cap back onto the bottle and place the second balloon over the cap of the bottle such that the mouth of the balloon is wrapped around the cap. Use the rubber band to keep the balloon in place.
The setup is complete, squeeze the bottle in quick successions with your finger placed over the hole you cut in the bottle. The balloon will fill up but will not deflate when you stop squeezing the bottle.
The air inside the balloon will apply pressure on the balloon piece and keep it closed, trapping the air in the balloon within the balloon.
That’s all there is to it, you’ve made your own air pump.
Here’s a video by NewKew that demonstrates this entire experiment: