At first, we rolled the A4 paper in a cylinder shape, and blew the balloon and held the mouth of the balloon to make sure that the air is trapped in the balloon.
Next, one person hold the cylinder shape paper straight and place the ping pong ball on the top end of the paper, then the other person move the balloon to the bottom of the paper. Lastly, the person holding on to the balloon will release the air in the balloon, and the air will be released into the cylinder paper and eventually reach to the ping pong ball and push the ping pong ball up.
But this did not work out as our ping pong ball remain stay on the top of the cylinder paper, and we were stuck at the moment and wonder what goes wrong with our design. Our teacher pointed out our mistake saying that we may try to change the length of the cylinder paper.
Thus, we cut the cylinder paper and make it shorter. Then we using the shortened cylinder paper to do the exercise again, and to our surprise we manage to blow up the ping pong ball to a certain height. And the ball was quite stable in the air when it is being blown up.
And eventually we also know what our mistake is in the starting of the exercise. Because when the length of the cylinder paper is too long, there would be more friction being created along the cylinder. Moreover, the chance that the air getting run off is also very high. Thus the solution is to cut the cylinder paper short to reduce the friction and kept as more air as possible inside the cylinder paper.