What you need:
Several lightweight plastic bags (identical)
Scissors
Clear tape
What to do:
1. Cut off the tops (handles) of each of the bags. Now cut off the bottoms of all the bags except one. (You can use five to seven bags but they need to be really lightweight)
2. Now, on a flat surface, arrange the bags in the shape of a tube. The mouth of one bag should align with the bottom of another. The end of the tube should be the bag whose bottom is intact.
3. Tape all the bags together in the shape of the tube. Check the bags for any tears and tape them up too.
4. Once the long bag is ready, try inflating it by breathing into it. How many breaths do you need?
5. Let all of the air out from the bag again.
6. Ask someone to hold the closed end of the bag straight and horizontal for you.
7. Now, hold the mouth of the long bag open and away from your mouth (at least 25 cm away) and blow a big breath of air into it. Quickly seal the mouth with your hand.
What happens:
When you try to inflate the bag, you put your mouth against the opening of the bag and blow into it. This technique needs a lot of breath before the bag inflates fully.
When you hold the bag away from your mouth and blow into it, it inflates faster and may even inflate fully in a single breath!
Why?
Daniel Bernoulli, an 18th-Century Swiss mathematician and physicist, is remembered for giving us something known as Bernoulli’s principle that applies to moving fluids (since air flows, it is also considered a fluid). According to this principle, the faster the air flows over a surface, the less it pushes on the surface i.e. the pressure exerted by the air decreases when its speed increases.
When you blow a big breath of air slightly away from the mouth of the bag, you increase the speed of the air molecules flowing into the bag. This creates an area of low pressure inside the bag’s mouth. But the surrounding air still has higher pressure so it pushes into the bag to equalize the low pressure your breath created. Thus, the bag inflates faster because the surrounding air is pushed into the bag along with your breath.
On the other hand, when you breathe directly into the mouth of the bag, only the air from your lungs goes into the bag. That is why it takes longer to inflate.
Picture Credit : Google
