Pressure fountain

Marvin and Milo Dec 15

What you need

A plastic bottle
Scissors
A straw
Putty
Food colouring
A balloon

Instructions

Make a small hole about 10 cm from the bottom of the bottle, stick the straw through it till half remains outside, pointing upwards Seal the hole with putty.

Fill the bottle halfway with water dyed with the food colouring. No water will come out of the straw.

Blow up the balloon, keeping the air inside as you stretch the neck over the top of the bottle, then release. Water spurts from the straw as the balloon deflates!

Results & explanation

Air presses down equally on the water in the bottle and in the straw at first, but attaching the inflated balloon increases the air pressure in the bottle. As it deflates, the air presses down on the water, pushing it through the straw.