Experiment 1:
The Funnel and the Ball
Materials:
1. One long-stem funnel (glass or plastic).
2. One ping-pong ball.
Procedures:
1. Place the funnel and the ball next to each other on the table.
2. Ask: "How can I pick up the ball with the funnel with out sucking through it? I may not touch the ball."
3. Pick up the funnel by the stem, place it over the ball and blow through the stem, lift the funnel while blowing.
4. Hold one hand under the funnel and stop blowing (ball drops).
5. Place the ball in the funnel and have a student try to blow it out of the funnel (he/she will not succeed).
Explanation:
The ball can be picked up from the table with the funnel by blowing through it. By blowing through the funnel, we create a lower pressure inside the funnel, especially at the spot where the stem is attached to the conical shape of the funnel. Here the fastest flow of air occurs, because the air molecules have suddenly more space to move about. The faster the flow of air, the lower the pressure. This is why the ball is sucked into the funnel by blowing, and for the same reason it is not possible to blow the ball out of the funnel. The harder we blow through the funnel, the lower the pressure gets in the mouth of the funnel.
Experiment 2:
The Clanging Soda Cans
Materials:
Two empty soda pop cans
About two dozen straight drinking straws
Procedure:
1. Spread the straws parallel to each other on the table and leave about 1/2 to 1 cm gap in between them.
2. Place the two cans upright about 2 cm from each other on the straws and show the students that they can easily move closer or further apart.
3. Ask: "What will happen to the cans if I blow in between them?"
4. Now spread the two cans about 5 cm apart. Ask: "Do I have to blow softer or harder to get the two cans clanging together?" Blow harder!
5. Now place the cans about 20 cm apart. Ask: "Can I still get the two cans clanging against each other?" Take a deep breathe and blow a constant stream of air on the right side of the left can and move your head towards the right, while constantly blowing. (cans will clang.)
Explanation:
Blowing in between the cans created a flow of air and thus a lower pressure compared to the stationary air on the other side of the cans. It is this lower pressure that drew them together. Theoretically, the cans could be placed an infinite distance away from each other and still be drawn together, as long as a constant flow of air on one side of one can moves along with it, to move it to the other can. Indeed, the faster the flow of air, the lower the pressure it exerts. But for the cans that were placed 20 cm apart, only a constant flow that could move with the can, was necessary.
Experiment #3
The attracting spheres
Materials:
Two plastic spheres (tennis balls or apples will work.
two lengths of thread (about 40 cm) and adhezive tape.
Procedure:
1. Tape the two pieces of thread to the two spheres.
2. Hang the two spheres about 3 cm apart from a horizontal support, or let someone hold them.
3. Ask: "What would you expect the balls to do when I blow in between them?" (anticipated answer: fly apart)
4. Blow in between the two hanging spheres and observe the movement of the two spheres. (hard plastic spheres will click together).
Explanation:
When blowing head on against one sphere, we observe that the sphere moves away from the source of the air flow. This is because the air molecules bump directly against the surface of the sphere, the kinetic energy is transferred to the sphere and it is thus pushed away. when blowing in between the two spheres, we are actually pushing away the air molecules and thus creating a lower pressure. The stationary air surrounding the two spheres on the outside exerts a higher pressure and pushes them against each other.
Applications of Bernoulli's Principle with spheres are encountered in playing tennis or baseball. A top spin in tennis creates a stronger and faster air flow under the ball and curver the path down (in court). A spin throw of a baseball curves the ball path in the Direction of the spin.
Experiment #4
The Leaping Egg
Materials:
Two identical wine glasses (or plastic cups)
A hard boiled egg (or a ping pong ball)
Procedures:
1. Place the two wine glasses or cups about 2-3 cm apart on the table and secure them down with tape or just hold them down.
2. Put the hard boiled egg in one of the glasses (or the ping pong ball in one of the cups) ask the audience the question: " How can I move the egg from one glass to another with out touching the egg. and leaving the glasses how they are?"
3. Most people will respond with "it's impossible!" No
Now blow a short hard puff obliquely into the far side of the wine glass that holds the egg and watch the egg leap! ( it may take a few practice blows to make the egg leap.)
Explanation:
Blowing obliquely into the far side of the glass builds the pressure on the side. It pushes the egg or ball out of the glass and flowing air above both glasses guides the egg towards the seond glass, because the flowing air actually creates a lower presssure. The harder we blow, the farther the second glass can be placed to catch the leaping egg.
Experiment #5
7-up experiment-
Materials:
large cylinder
2 cans of 7-up per student group
macaroni (16oz)
grapes, peeled and unpeeled
lamp or flashlight
Procedure:
1. Pour 7-up in the cylinder
2. Turn light on and face at base of cylinde.
3. Have students observe what happens to the bubbles in the 7-up.
4. Put in some macaroni, and have students observe the bubbles attaching to the noodles and bringing them to the top. They will roll over and start to fall, then come back to the top.
5. Have them try the same thing with both kinds of grapes.
Explanation:
The bubbles attach to the macaroni while they are at the bottom of the cylinder. The air pressure at the bottom forces the bubbles to move upwards. Once the macaroni reaches the top, the bubbles will start popping, causing the macaroni to roll and fall again. The same thing happens with the grapes.