Bernoulli Effect

Michael McIntosh               Whitney M. Young Magnet High School
                               211 S. Laflin St.
                               Chicago IL 60607
                               (312) 534-7539

Objective:

This lesson will show the relationship between velocity and pressure of a fluid. 
The demonstrations should be appropriate for all levels.  The explanations may 
be more suitable for upper level and high school. 

Materials Needed: 

1. Coat hanger and two strips of paper (about 4 cm X 12 cm)
2. Hair blower and ping-pong ball
3. Ruler and strip of paper (about 2.5 cm x 5 cm)
4. Two aluminum cans connected by a string (about 1 m long)
5. Bits of paper and whee-o (thin flexible tube, similar to vacuum cleaner 
   hose, about 3 cm diameter and 50-75 cm long)
6. Thread spool, straight pin, and index card
7. Funnel and ping-pong 
8. Long narrow plastic bag (two newspaper covers taped together work well.)

Procedures:

Explain each of the items and ask for predictions about what will happen in each 
case.  Demonstrate each of the items or have the students go through each 
procedure and make observations. 

1. Cut off the long side of the coathanger and bend the other sides so that they 
   are parallel to each other. Tape the strips of paper to opposite sides so 
   that they hang down parallel to each other.  Blow down between the two 
   strips. 

2. A hair blower with a straight nozzle works well.  
   A paper cup with the bottom cut out stuck on the end of the blower also 
   works.  Turn on the blower and place the ping-pong ball in the air stream.  
   Tilt the blower. 

3. Tape the paper to the ruler so that it forms an air foil.  Place a 
   pencil on a table and place the mid point of the ruler across the pencil.  
   Blow across the top of the paper. 

4. Hang the cans so that they are at the same level and about 2 cm apart.  Hold 
   a ruler behind the cans and blow between the cans.  (This also works with two 
   apples or two balloons.) 

5. Hold the bits of paper in one hand.  Place one end of the whee-o over the 
   paper and twirl the whee-o.

6. Stick the pin through the index card and then into the hole on one side of 
   the spool.  Blow into the other hole of the spool.

7. Place the ping-pong ball in the funnel.  (The top part of a plastic bottle 
   makes a good funnel.)  Blow up through the small end of the funnel.

8. Challenge someone to blow up the bag with as few breaths as possible.  It 
   will take about five breaths.  Flatten the bag.  Then claim to be able to 
   blow it up with one breath.  Hold the bag open and quickly blow into the bag 
   from about 30 cm away. 

Observations:

1. The bottom ends of the strips will move closer together.
2. The ball will rise and float in the air stream.
3. The end of the ruler with the air foil will rise.
4. The cans will move closer together.
5. The bits of paper will be sucked up into the whee-o.
6. The card will remain in place.
7. The ball will stay in the funnel. 
8. The bag will fill with air.

Explanations:

The higher the velocity of a fluid, the lower the pressure.  This is called the 
Bernoulli Effect.  Each of these activities demonstrate the Bernoulli Effect.

1. The velocity of the air is greater between the two strips.  Therefore the 
   pressure is lower between the strips.  The higher pressure on the sides 
   pushes the strips together. 

2. The air in the stream is faster than the air outside the stream.  The higher 
   pressure outside the stream keeps the ball in the stream.

3. The air above the air foil is faster than the air below.  The higher pressure 
   below pushes the air foil up. 

4. The air between the cans is faster than the air on the sides.  The higher 
   pressure on the sides pushes the cans together.

5. The air inside the whee-o is faster than the air outside.  The higher 
   pressure outside pushes the paper into the whee-o.

6. The air between the spool and card is faster than the air on the opposite 
   side of the card.  The higher pressure on the opposite side pushes the card 
   against the spool.

7. The air is faster below the ball and on the sides.  The higher pressure above 
   the ball pushes the ball down into the funnel. 

8. The air inside the bag is faster than the air outside the bag.  The higher 
   pressure outside pushes the air inside.