Rockets lift off and their detachment from the ground is due to the fact that the rocket expels fuels backwards, while at the same time air pushes rockets forward.
Pass the rope through the straw. Stretch the rope and fasten one end to the wall. Place the balloon along the straw. With the sellotape, fix the balloon to the straw so that the balloon’s mouth is towards the ground. Let the balloon go and watch the take off!!
Air is launched backwards from the balloon’s spout. The force that pushes the air backwards results in the appearance of an opposite force (action – reaction) that moves the balloon forward.