Students will observe the generation of a swirling mass of air that travels quickly as a result of a change in air pressure within the constructed air cannon.
Associated Curriculum Topic
- shower curtain
- 10 -25L plastic garbage can
- duct tape
- exacto knife
- drumstick (or 30 cm ruler)
- plastic cups
- a candle in a stable holder, matches
- smoke machine if you have access to one!
Fluids are essential to many industrial processes and form the basis of hydraulic and pneumatic devices. Any substance that flows is considered to be a fluid. This includes such things as water, shampoo, sunscreen, and honey. Even gases, such as air, can be classified as fluids. In this activity students will be introduced to the concept of air pressure, through the use of an air cannon. The air cannon is designed so that when a tight skin is struck, a quick burst of air is shot out from the front of the cannon. When the skin is struck, the air molecules are suddenly forced closer together, which increases the pressure inside the garbage can. Since the area of the hole in the bottom of the garbage can is much smaller than the area of the skin, the increase in pressure causes a quick burst of air to flow outwards from the garbage can in the attempt to reduce the sudden increase in pressure inside the garbage can. If the air inside the garbage can were replaced with smoke, one could see that the sudden outflow of air would create a ring of smoke. As the smoke ring travels away from the cannon it increases its radius because of the decrease in pressure compared to the pressure inside the garbage can.
- with the exacto knife, cut a softball-sized hole in the bottom of the garbage can
- flatten the shower curtain on the floor and place the garbage can upside down on top of the curtain
- draw a line around the garbage can, leaving a gap of about 3’’ between the line and the edge of the garbage can
- cut out the circle on the shower curtain and attach it to the top of the garbage can with duct tape (attach the curtain to the garbage can so that there is as much tension on the curtain as possible)
- if you have access to a smoke machine, fill the inside of the garbage can with smoke
- place the plastic cups on a desk about 5-10 feet away from you, aim the opening of the cannon at the cups and tap the shower curtain with the drumstick (or ruler) – should be a strong enough shot of air to knock over the cups
- place the candle in its holder about 5-10 feet away from you, aim the opening at the candle and tap the shower curtain with the drumstick – should be able to blow out the candle
- experiment with how far away the air cannon can be from the cups and/or candle and still be effective
- Why did the cups fall over?
- Why did the candle go out?
- Would the same result occur if there were a larger hole in the bottom of the garbage can?
- What does striking the shower curtain do to the air inside the can?
- Why does the smoke ring expand as it travels away from the cannon?
- The finished project should be similar to the photos below.