To make your balloon hovercraft the first thing that you need to do, is take the pop top from your plastic bottle and place it over the hole in the middle of your CD. You are then going to secure it in place. You can either do this with a glue gun or with strong tape. You will need to make sure that no air can escape at the join.
The way the hovercraft works is that air from the balloon is released and gets trapped beneath the CD. This trapped air reduces the friction between the floor and the CD. As air is released from the balloon it allows the hovercraft to glide across a surface on a current of air.
You may like to try out your hovercraft on different surfaces and see how they compare.
You could also try swapping the CD base and trying something like a paper plate and see if this makes a difference...
The video tutorial for this activity is available on the Surrey Libraries YouTube Channel