My daughter has a big interest in flight. On Fridays we work on lessons that will teach my daughter about flight. Today’s lesson focused on Bernoulli’s Principle. Bernoulli’s Principle is that faster moving air has a lower pressure than slower moving air. We started out watching a video called Bernoulli’s Principle – Easiest Way Explained on youtube.
We did an experiment using a Wind Bag. To make a hypothesis about the wind bag I asked my daughter how many breaths she thought it would take to fill up the wind bag. We wrote that down.
Then what I did was tie the end of the wind bag into a knot. I had her walk backwards until we could make it straight. Then I had her blog 5 breaths into the bag with her mouth on the bag like you were blowing up a balloon. Then we scrunched the air to the end of the wind bag. This is what 5 breaths looked like.
Next I had my daughter let the air out of the wind bag. This time. I held the end of the bag. I had her open her bag with the opening kept wide, and about 10 inches from her mouth, I had her blow a quick breath. This time the whole wind bag was full of air in one breath. You can see the video here.
Now lets explain the reasoning behind this…. when my daughter blew five breaths into the windbag she was actually cutting off the supply of air flow. Now when she did the windbag from a distance and blew into the bag the air outside of the bag was a higher pressure and it pushed the air towards the area of low pressure to the center of the wind bag. What is fascinating is this also applies to lift with an airplane. You have the lower pressure; faster air that goes over the wing and creates a suction which moves the air up. The slower air pressure; higher pressure helps to push the wing up….which is responsible for lift…
I really thought this experiment was a great hands on approach to air pressure. It also gave us a visual as to what is responsible for lift in a wing of the plane.
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