Prepared By : Mr.Leon JJ Super Education3.6 UNDERSTANDING BERNOULLIS PRINCIPLEBernoullis Principle(1m)Bernoulli's Principle states that as the speed of a moving fluid (liquid or gas) increases, the pressure within the fluid decreases.

Venturi Effect is the fluid pressure that results when an incompressible fluid flows through a constricted section of a pipe.

V2> V3> V1P1> P3> P2

Experiment 1

Figure above shows that when water flow from left to right, the water level decreases from left to right. This indicates that, the water pressure decreases from left to right.

Explanation:Liquids flow from places with higher pressure to places with lower pressure.

However, if the experiment is repeated by using a Venturi tube where the diameter at B is made smaller than A and C as in the diagram above, the water level become lowest at B.

Explanation:The pressure at B is the lowest because the liquid flow the fastest at B. According to Bernoulli's Principle, the faster the water flow, the lower the water pressure.

Experiment 2

Figure above shows some air is blow through a tube from left to right. The water level in the capillary tube increases from left to right.This indicates that the pressure in the tube decreases from left to right.

Explanation:Gases flow from places with higher pressure to places with lower pressure.

However, if the tube is replaced by a Venturi tube, the water level become highest at B. This indicates that, the pressure of the air is the lowest at B.

Explanation:The pressure at B is the lowest because the gas flow the fastest at B. According to Bernoulli's Principle, the faster the gas flow, the lower the gas pressure.

2.Figure below shows an . The upper region of the aerofoil has higher air velocity than the lower region of the aerofoil. By Bernoullis principle, the lower region has . pressure than the upper region of the aerofoil. This causes a on the aerofoil.

Experiment 1

A paper will be lifted upwards when air is blown rapidly above it.

Explanation:1. Air move rapidly above the paper, causes the pressure above the paper to decrease.2. Pressure below the paper becomes relatively higher.3. Owing to the difference of the pressure, a net force is produced to push the paper upward.

Experiment 2

When air is blown rapidly between the 2 ping pong balls, the 2 balls will move towards each other.

Explanation:

1. Air move rapidly between the 2 balls, causes the pressure between the 2 balls to decrease.2. Pressure at the other side of the balls becomes relatively higher, push the 2 ball close to each other.

Experiment 3

The ping pong ball will not fall when water is allowed to flow through the filter funnel.

Explanation:1. Water above the ping pong ball flow rapidly, causes the pressure above the ping pong ball to decrease.2. As a result, the pressure below the ping pong ball is relatively higher.3. Owing to the difference of the pressure, a net force is produced to push the ping pong ball upward.

Exercise 3.61. Air

C B A

Glass tube of non-uniform diameter

Atmospheric pressure

Air flows through a horizontal tube as shown in the figure causing water columns to rise in three vertical glass tubes. Compare and tabulate the value of air velocity and pressure in the three positions A, B and C of the horizontal tubes.

Answer:A B C

VelocityLowHigh Moderate

PressureModerate

2. Figure below shows a Bunsen burner and a carburetor. Mark with X for low pressure area. Bunsen burner

Carburetor

Application of Bernoullis Principle**************************Aerofoil

According to Bernoulli Principle: Air moves with higher speed over the top of aerofoil. This creates a region of lower pressure over it and a region of higher pressure below it. This difference in pressure produce a resultant force acting upwards on the wings.Q & AQ:Explain how an upthrust is produced when the aeroplane is moving.

A: When the aeroplane is moving, air flows faster above the wing than below. Therefore, the air pressure below the wing is higher than above. The difference in air pressure produces a net force acting upwards.

Spinning Ball According to Bernoulli Principle, a ball which spins in the same direction of moving air will increase the velocity of the ball. The moving air in the opposite direction of the spin ball is slowed down. Higher velocity will produce lower pressure and vice versa. Because of this, the air pressure on one side is higher than that the other side. It produces a resultant force acting from high pressure to low pressure. Therefore, a spin ball curves.

Insecticide Spray

1. When the plunger is pushed in, the air flows at a high velocity through a nozzle.2. The flow of air at high velocity creates a region of low pressure above the metal tube. The higher pressure of the atmospheric air acts on the surface of the liquid insecticide causing it to rise up the metal tube.3. The insecticide leaves the top of the metal tube through the nozzle as a fine spray.

Bunsen Burner

1. When the burner is connected to a gas supply, the gas flows at high velocity through a narrow passage in the burner, creating a region of low pressure.2. The outside air, which is at atmospheric pressure, is drawn in and mixes with the gas.3. The mixture of gas and air enables the gas to burn completely to produce a clean, hot, and smokeless flame

Carburetor

A carburetor is a device that blends air and fuel for an internal combustion engine. Figure above shows how Bernoulli's principle is applied in a carburetor to mix the air with the fuel.

Q & AQ:Explain why 2 fast moving boats tend to move closer to each other.

A:1. When the two boats travel at high speed, the stream of fluid (air and water) between the boats flow faster than the other sides of the boats.2. This form a low pressure zone in between the boats.3. The higher pressure at the other sides of the boat pushes the boats closer to each other.8 | Page