What you will need:
- Large dry cleaner bag
- Adult supervision
- Squeeze all of the air out of your dry cleaner bag.
- Use both hands to hold the mouth of the bag so that you can blow air into the bag, then squeeze it closed to trap the air inside. Begin taking breaths and blowing air into the bag to see how many breaths it will take to completely fill up the bag with air. Note that the other end of the bag does have small hole so you will never completely fill the bag unless you seal those holes first. For this experiment, we do not need to seal the holes as we are just trying to see approximately how many breaths it would take to fill the bag up with air.
- Squeeze all of the air back out of your dry cleaner bag again.
- This time, we will use what is known as Bernoulli's Principle to fill the bag faster. Hold the mouth of the bag open but make sure that the opening is at arm's length.
- Take a deep breath and blow as hard and as long of a breath as you can directly into the opening as if you were trying to blow out a candle. DO NOT move your head closer to the bag as you blow. In order to take advantage of Bernoulli's Principle, you must keep the opening at arm's length from your head as you blow into the bag.
- If done correctly, you will notice that you can now fill the entire bag with one or two breaths.
What is going on?
The air that is all around us is actually exerting a force on us due to the weight of the air above us. This is known as atmospheric pressure, which is about 14.7 lbs per square inch. Almost 300 years ago, Daniel Bernoulli figured out that moving air actually has less pressure. This is known as Bernoulli's principle. By holding the bag at arm's length and blowing into the opening, you are creating an area of lower pressure air going into the bag. Since this area of faster moving air has less pressure, the air around it will rush in to fill that lower pressure area and actually get pulled into the bag as well. By using Bernoulli's principle, we are not only blowing the air from our lungs into the bag, we are also including a lot of air from the room around us causing the bag to fill up much quicker.
Since moving air has less pressure, try cutting a strip of paper about 1” X 11” Now hold one end of this strip of paper just under your bottom lip. Make sure that the paper is laying over your finger as you hold your finger to your face as shown. As you blow, the moving air ABOVE the paper should cause the paper to lift up due to the fact that there is less air pressure on top of the paper. Remember that the air below the paper is not moving, therefore it is still at 14.7 pounds.
BTW, forgive my crude drawing (or should I say my “attempt”) of a facial profile. I did this in word format and do not claim to be an artist!