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Title: Bernoulli's Principle
Principle(s) Investigated:
- Bernoulli's Principle
- Pressure Differentials
- Atmospheric Pressure
- Measuring Pressure
Standards : Paste in the appropriate California content standards.
8th grade Physical Science
Materials: In this lab there will be three stations that students will move between. Here is what each station will need in the class I am teaching:
Station one: air stream between two objects
- two empty soda cans per group
- two 6-inch lengths of string per group
- one piece of paper per group
- one cup of straws per table (to be thrown away after use)
- meter stick (or anything that can used to suspend the soda cans in the air)
Station two: measuring pressure with a straw-manometer
- food coloring
- one beaker or transparent cup per group
- one cup of straws per table (to be thrown away after use)
Station three: atomizer
- food coloring
- one beaker or transparent cup per group
- one cup of straws per table (to be thrown away after use)
- scissors
- notebook or computer paper
Procedure:
Throughout the lab students will be filling their answers out within this ---> Google form <--- (http://goo.gl/ko7TEG)
Station one: Air stream between two objects
1. Tie a knot around the tab of each soda can.
2. Wrap the unattached end of string around the meter stick so that the balls are hanging at the same height as well as within 2 cm of each other.
3. Use a straw to blow air between the cans and note the movement of each, as well as the areas of high and low pressure.
4. Predict where you would have to blow to make the cans move outwards, then test your prediction and note the areas of high and low pressure.
5. Fold a sheet of notebook paper as shown in the diagram
6. What do you think will happen when you blow underneath the bridge? Test your prediction and note the areas of high and low pressure.
Station two: Measuring pressure with a straw manometer
1. Will the water level in the straw move up or down if you blow across its tip using another straw? Make a prediction in the form and test it out! Be sure to indicate the areas of high and low pressure.
2. Now squeeze the tip of the horizontal straw (the one you are blowing through) and try again. Does the level change even more than before?
When you are not blowing through the straw, the air pressure is the same both above the straw and above the water. Both are open to the atmosphere and experience the same air pressure, approximately 1,013 millibars. Every centimeter that the water rises represents one less millibar of pressure, so now we need to:
1. Determine how high the water will rise in the straw when you blow
2. Calculate the change in air pressure (in millibars, or mbar)
Station three: Atomizer
1. Shorten the straw that you used in part 2 so that fluid will rise to the top of the straw when you blow across its open end.
2. Put a few drops of food coloring into the beaker and use your straw to spray a mist of water onto a sheet of paper.
3. What are some other devices that you can think of that use Bernoulli's principle to atomize (reduce into fine particles) and spray a liquid? ex. a perfume/cologne bottle
Student prior knowledge:
Prior to this activity we will have already lectured on Bernoulli's principle. Students will be familiar with the definition of Bernoulli's principle (the faster a fluid increases, the less pressure it exerts), as well as with the term lift and how it applies to objects in flight.
Explanation: Give a thorough explanation of the experiment or demonstration. Your explanation should be written to give your fellow teachers a solid understanding and include greater detail than what you might provide for your secondary students. Make certain to include equations whenever pertinent.
Questions & Answers:
1. Given only two straws, how can you separate the hanging soda cans without blowing directly on them?
2. Hurricanes and tornados may cause houses to explode. Based on what we have just learned in this lab, why do you think this occurs?
3. Why is it dangerous to stand too close to a fast moving train as it passes by?
Applications to Everyday Life:
Bernoulli's principle influences numerous events that we witness and experience in our day to day to life. Perhaps the most common example is in how airplanes are able to fly. Due to the shape of their wings, airplanes cause air to move at different speeds above and below their wings. Because the air moving over the top is moving faster than the air stream below the wing, it produces the lift necessary to keep the plane in the air.
Another example of bernoulli's principle in everyday life is the chimney. Hot air naturally rises upwards, but it is also aided partly because it is pushed upwards. As wind passes over the top of the chimney it creates an area of low pressure, so the smoke moves from the higher pressure area near the bottom to the low pressure top.
Bernoulli's principle is also in effect when you drink from a straw! By sucking through a straw you create an area of low pressure within the straw, allowing the surface pressure of the liquid to push it into the straw for you to drink.
Photographs: Pictures are provided throughout the activity, I will add classroom photos when the activity takes place.
Videos: Include links to videos posted on the web that relate to your activity. These can be videos you have made or ones others have made.
References: Herr, N. and Cunningham, J. (1999) Hands-on Chemistry Activities with Real-Life Applications San Francisco Jossey-Bass
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