We can see Bernoullis principle here too. each ping pong ball has been glued to the end of a straw and placed vertically. if we blow air between the two ping pong balls, what do you think will happen?
(a) the Ping pong balls move apart
(b) the ping pong balls do not move at all
(c) the ping pong balls move to the center
.......The ping pong balls move together because of Bernoulli’s principle. The region with the fast moving air is between the ping pong balls so both ping pong balls get pushed into this low pressure region by the higher pressure non moving air region! (add words to slo mo pic or extended frame)
(expt A photo) What do you think would happen if we had fast moving air on all sides of a ping pong ball? (picture of ping pong ball with arrows going around on all sides and picture) (and video ) (don’t read choices on any expt!)
(a) the ping pong ball would shoot straight up
(b) the ping pong ball would fall to the ground
(c) the ping pong ball would float
(Words part B start) Let’s try it using a ping pong ball placed on a hair dryer!.........
with fast moving air on all sides of the ping pong ball, the ball floats and remains the column of air because once the pull of gravity and the lift of bernoulli’s principle become balanced!
(expt B use BETTER one) Let’s play around with this a little bit. What do you think would happen if a tube is placed below the ping pong ball in the column of air?
(a) the ping pong ball becomes unstable and falls out of the column of air
(b) the ping pong ball increases its height with the tube in place
(c) no change in height of the ping pong ball in the column of air
Let’s try it! ................the placement of a tube in the column of air below the ping pong ball allows the ball to increase its height in the column of air. This is because the tube collimates the air; increasing the speed of air around the ball allowing the ball to go higher than without the tube!
(expt C)
What do you think will happen if the tube is placed in a column of air containing two ping pong balls?
(a) they collide and fall out of the column of air
(b) they fall through the tube together
(c) only one falls through the tube but remains in the column of air
Ok, now what does all this have to do with flying? Modern aircraft generate lift two ways. One way is the same way kites and the Wright Brother’s glider generated lift...(newton’s 3rd law, or deflection of air) (images) However modern aircraft also generate lift through Bernoulli’s principle. Modern aircraft do not have flat wings like kites and the WRight’s glider. Modern aircraft wings are curved on top. and look like this. (drawing). Let’s say the air is moving in this direction...(arrows) so air is moving under and over the top of the wing. since the wing is curved on top the air on the top of the wing has a further distance to travel than the air on the bottom of the wing. Since the air on top of the wing has farther to go it travels faster. faster moving air generates lower pressure so a curved wing generates a pressure difference between the top and bottom of the wing generating lift! (words appear) ......up, up, and away!
review
Let’s review.
Early wings were flat similar to a kite and create lift through deflection of air
modern wings create lift through deflection of air and bernoulli’s principle
bernoulli’s principle states that faster moving air generates less pressure than slower moving air
modern wings are shaped such that there is faster moving air on top of the wing than on the bottom of the wing. the resulting pressure difference is the lift necessary for planes to fly!
