In the Classroom

Science Discipline(s)

Chemistry, Physics, Physical Sciences


Vortexes, Pressure, Air

Activity Title

Smoke Ring Vortex


  • 2- 5 Gallon trash cans (plastic)
  • Thick trash bags or 1 shower curtain
  • Smoke bombs
  • Lighter
  • 1 Bungee cord or tape, very long
  • 3 paint buckets



  • Cut an opening (approximately 3-6 inch diameter) at the base of the trash can or in a cardboard cover for the laundry hamper. (Figures 1 and 2)If using a trash can, place the trash bag over the mouth of the trash can. Place the bungee cord around the trash bag. If using tape, tape the bag down tightly. Make sure the bag is really taut. (Figure 3)
  • Place the end of the fog machine (where the fog comes out) into the hole so that the fog can
  • Once the fog has accumulated, you can begin the demonstration.
  • A whirling smoke ring vortex should be ejected from the trash can.


Trash bin

Figure 1

Trash bin 2

Figure 2: Spiral Pop-Up Laundry Hamper


Trash bin 3

Figure 3



What factors do you believe influence the size and speed of the smoke ring? How could you design an experiment to test your hypothesis?

How could you measure the speed of the smoke ring and how it depends on the above factors?

What causes the air to shoot out of the trash can?

Why does the ring shape form?

What happens if we change the force with which we strike the trash bag?

Is the vortex still there if there is no smoke in the trash can?



When the shower curtain or trash bag is lightly tapped, there is a change in pressure inside the paint bucket. This change in air pressure causes air to rush out of the bucket in a ring or donut shape.  We call this donut-shaped ring a torus. The air on the inside is moving faster than the air on the outside of the ring, holding the donut shape as it travels through the air.  These rush of air can be felt if the bucket is aimed at someone. In order to see the torus, we add fog to the inside of the bucket. Once the bucket is filled with fog, the donut-shapes can be observed shooting out of the bucket because the smoke takes the torus shape. If the shower curtain or trash bag is tapped lightly, the torus can be observed and the air in the center can be seen traveling outward toward the outside of the ring. If you tap it harder, you can shoot smoke rings. Try to shoot targets with these rings!



Care should be taken with the fog generator since parts become quite hot. Do not allow children to handle the fog generator.


Next Generation Science Standards

K-PS2-1. Forces and Interactions: Pushes and Pulls   

Plan and conduct an investigation to compare the effects of different strengths or different directions of pushes and pulls on the motion of an object.

K-PS2-2. Forces and Interactions: Pushes and Pulls   

Analyze data to determine if a design solution works as intended to change the speed or direction of an object with a push or a pull.

5-PS1-1. Structure and Properties of Matter

Develop a model to describe that matter is made of particles too small to be seen.