Overview
Bernoulli's principle states that in fluid flow (which includes air), as the velocity of a fluid increases, its pressure decreases. The students will discover that the faster air moves, the lower the pressure becomes within that flow of air. They will see this effect by blowing between two soda cans.
| TOTAL TIME | 5 minutes |
|---|---|
| SUPPLIES | Two (2) empty soda cans, a level surface |
| PRINTED/AV MATERIAL | None |
| TEACHER PREPARATION | None |
| SAFETY FOCUS | Tornado safety |
Procedure
- Lay the two cans on their sides parallel to each other, about one inch apart, near the edge of a level surface.
- Ask the students to predict what will happen when air is blown between the cans: Will the cans move apart or together? Have them explain why they made their prediction.
- Put your face down near the surface and blow lengthwise between the two cans.
- It will take some trial and error, but eventually the two cans will roll together.
- Another way to demonstrate is by suspending two cans on string about an inch apart and have the student blow between them.
Discussion
Students may expect the cans to move apart as air is blown between them, however, the opposite occurs. This effect is Bernoulli's principle in action, named after the eighteenth-century Swiss mathematician and physicist Daniel Bernoulli. He discovered that the faster a fluid moves, the lower its pressure becomes. Because air is a fluid, this principle is important in understanding wind and weather conditions. It also has applications in aviation and airplane flight because it explains how planes generate lift as they increase in speed.
By blowing between the two cans, the air between them moves faster than the surrounding air, lowering the pressure between the cans. The cans roll together as the higher pressure surrounding the two cans (away from the air flow) pushes the cans together toward the region of lower pressure.
Building a Weather-Ready Nation
There is no such thing as guaranteed safety from a tornado, but taking the appropriate steps can drastically increase the chances of survival. The most violent EF-5 tornadoes can level and blow away almost any home, but fortunately the most common tornadoes are much weaker.
At home, have a family tornado plan based on the kind of dwelling in which you live, and practice a family tornado drill at least once a year. In a tornado, the appropriate safety action is to go to your basement, safe room, or an interior room away from windows, putting as many walls between you and the tornado as possible. Flying debris is the greatest danger in tornadoes, so cover your head with your hands or protective coverings (e.g., mattress, sleeping bags, thick blankets, etc.). After the tornado, let your family and close friends know through text or social media that you’re ok so that they are aware everyone is safe and accounted for.
When a tornado watch is issued, think about the drill, and check to make sure all your safety supplies are handy. Charge your cell phone and use local TV, AM/FM Radio, NOAA Weather Radio, and Wireless Emergency Alerts on your cell phone to stay alert for warnings. Forget about the old notion of opening windows to equalize pressure; a tornado can break even open windows, so stay away from glass.
If you are away from home, always remain weather aware, and take note of potential shelter areas in stores and restaurants so that you can seek shelter if a tornado approaches. All administrators of schools, shopping centers, nursing homes, hospitals, sports arenas, stadiums, mobile home communities, and offices should have a tornado safety plan in place, with easy-to-read signs posted to direct everyone to a safe, close-by shelter area.
Schools and office building managers should regularly run well-coordinated drills. If you are planning to build a house, especially east of the Rockies, consider an underground tornado shelter or an interior "safe room". For more information on what to do during severe weather, check out the NWS Seasonal Safety Campaign website.