What happens to a fluid (water or air) when it moves from entering a wide opening to entering a narrow opening?

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1 What happens to a fluid (water or air) when it moves from entering a wide opening to entering a narrow opening? The water (or air) speeds up. Since the same amount of water/air has to travel through a small space, it moves more quickly. Air, like water will speed up as it moves around an object or through a narrow channel. Air speed and pressure - Pressure decreases as speed increases. Fluid any substance that flows easily, both liquids and gases **Bernoulli's Principle** You must be able to explain Bernoulli s Principle on your test!! Background Information: We know: Air has areas of low pressure and high pressure. We can change air pressure by speeding it up. When there are areas of high pressure and low pressure, the air will try to balance those forces. High pressure will move into low pressure areas. Bernoulli's Principle In 1738, Daniel Bernoulli discovered that if the speed of air is increased, the pressure is lowered. With regards to flight, Bernoulli's Principle allows us to understand LIFT. The quicker the movement of air over the top of the wing creates a lower pressure area than what exists below the wing where the air is moving slower. As a result, the high pressure area below the wing pushes upward toward the low pressure area causing the wing to lift. It is lift that helps a bird stay aloft, causes a frisbee to fly and allows an airplane to fly.

2 In class demonstrations of Bernoulli s Principle: 1) You will need a piece of paper. Place the paper below your bottom lip and blow. Make a prediction...what will happen to the paper? 2) Use the same piece of paper from the last demonstration. Fold it in half to make a tent shape. Blow between the tent sides. Make a prediction...what will happen to the tent? How can a shower curtain demonstrate the same property? The force of the water in the shower creates moving air. This makes a lower air pressure area. The air on the outside of the curtain will be an area of higher pressure and would force the curtain inward toward the lower pressure area. Gravity is a strong force that pulls everything down to Earth, but it can be overcome by an upward force called LIFT.

3 How is lift produced? Lift is produced when the air pressure below a surface is greater than the air pressure on top of the surface. High Pressure Blowing air across the top of a piece of paper creates low pressure. The air below is not moving and is higher pressure. The high air pressure area forces the paper upward into the area of low pressure. Facts about Lift: 1) Lift depends on shape - Lift is greater with an airfoil shaped wing than with a flat one. 2) Lift depends on Angle of Attack - up to a point, lift increases as the angle of attack increases. 3) Lift depends on speed - Lift increases as speed increases. 4) Lift depends on direction - Lift acts perpendicular to the direction of the objects movement.

4 Brief Summary: Bernoulli's Principle Increase air speed lowers air pressure Air will move from high low If we decrease the air pressure above an object, we will create lift as the air moves from high to low pressure. AIRFOILS How is lift affected by the shape of an object? Curved surfaces affect lift. The curved top surface of an airplane wing and plane itself causes the air above it to move faster creating an area of low pressure. The name given to a curved shape is an airfoil.

5 Other important vocab: angle of attack: the angle created by the tilt of an aircraft s wing leading edge: the front edge of a wing, usually rounded trailing edge: the back edge of a wing, usually tapered How Can Heavy Objects Fly? In order for a plane to fly, the lift has to be greater than the weight. While the plane is flying level, the lift and weight must be equal. When the plane is descending, the lift will need to be less than weight. A pilot can increase lift during flight by changing the tilt of the wing. When the leading edge of the wing is tilted up, the pressure above the wing is reduced, and more lift is created. This is called angle of attack. Increasing the angle of attack, increases lift up to a point where the wing stalls. There is a point where if the angle is too great, the plane will not fly at all. The most important element in producing lift is speed. If the speed of the plane doubles, the result is four times the lift. Four forces act on flying objects: Drag Thrust Lift Gravity Gravity Drag is the opposite of thrust (Thrust must overcome drag to fly) Lift is the opposite of gravity (lift must overcome gravity to fly)

6 Drag The force that acts on an object to resist forward motion. Drag depends on three factors:(p. 23) 1) Shape - shapes that are long, thin and smooth, round at the front and tapered at the back will have low drag (airfoil shape) 2) Speed - Drag increase as speed increases 3) Direction - Drag acts in the opposite direction to the object's movement Videos which are helpful: Test will consist of multiple choice, matching and long answer questions (which you will need to answer clearly, with details and examples).