Shoot your own smoke ring vortex across the room
You will definitely need an adults help to prepare for this fun experiment. You will need a big round dustbin and must cut a circular hole out the bottom of the bin. An electric saw is the easiest way to do this. The hole should be between 15-24 cm in diameter but you do not need to be too accurate with this, a hole that is a decent size will work fine. Use some heavy duty tape to fix a shower curtain to the open end of the dustbin and for the ultimate demonstration you will need a smoke machine which can be purchased online or from many electronics, gadget or party stores.
Performing this experiment is easy. For the basic demonstration you can simply aim the vortex generating dustbin at a small object (paper cups work well) and make sure the circular hole is pointing at the target. Aim carefully and then give the shower curtain a thump to send a vortex shooting out across the room. If you have a smoke machine then fill the dustbin with smoke through the hole and then try again. This time you will see the vortex as it travels through the air.
The dustbin is full of air (or smoke) and as you thump it a pulse of air is pushed out through the hole. The air around the edge of the pulse travels through the hole and brushes the inside edge of the hole. This causes it to take longer to get out and it rolls back on itself in a circular fashion creating a smoke ring.