- Pressure Area The area of a surface is the number of square units that it covers. To find the area of a rectangle, multiply its length by its width. The area of the rectangle below is 2 cm X 3 cm, or 6 cm2.

What Is Pressure? - Pressure Pressure decreases as the area over which a force is distributed increases.

Pressure = Force Area Units Force Newtons (N) Area Meters squared (m2) Pressure N = Pascal (Pa) m2

Fluid Pressure - Pressure All of the forces exerted by the individual particles in a fluid combine to make up the pressure exerted by the fluid.

Variations in Fluid Pressure As your elevation increases, atmospheric pressure decreases.

Variations in Fluid Pressure Water pressure increases as depth increases.

Previewing Visuals - Pressure Before you read, preview Figure 5. Then write two questions that you have about the diagram in a graphic organizer like the one below. As you read, answer your questions. Pressure Variations Q. Why does the pressure change with elevation and depth? A. Air and water exert pressure, so pressure varies depending on how much air or water is above you. Q. How much greater is water pressure at a depth of 6,500 m than it is at sea level? A. It is about 650 times greater.

Buoyancy - Floating and Sinking The pressure on the bottom of a submerged object is greater than the pressure on the top. The result is a net force in the upward direction.

Buoyancy - Floating and Sinking The buoyant force acts in the direction opposite to the force of gravity, so it makes an object feel lighter.

Buoyancy - Floating and Sinking Achimedes’ principle states that the buoyant force acting on a submerged object is equal to the weight of the fluid the object displaces.

Buoyancy - Floating and Sinking A solid block of steel sinks when placed in water. A steel ship with the same weight floats.

Density - Floating and Sinking Changes in density cause a submarine to dive, rise, or float.

Relating Cause and Effect - Floating and Sinking Relating Cause and Effect As you read, identify the reasons why an object sinks. Write them down in a graphic organizer like the one below. Causes Weight is greater than buoyant force. Effect Object is denser than fluid. Object sinks. Object takes on mass and becomes denser than fluid. Object is compressed and becomes denser than fluid.

Pressure P = F N A m2 Pascal’s Principal Pressure applied to a fluid in a closed container is transmitted equally to every point of the fluid and to the walls of the container.

Hydraulic Lift P1 =P2 Therefore: F1 = F2 A1 A2 F2, A2 F1, A1

How Airplanes Wings Work

Click the Video button to watch a movie about density. - Floating and Sinking Density Click the Video button to watch a movie about density.

Bernoulli Principle: States that as the speed of a moving fluid increases, the pressure within the fluid decreases

Bernoulli’s Principle is what allows birds and planes to fly. The secret behind flight is ‘under the wings.’

AIRFOIL On top: greater air speed and less air pressure On bottom: less air speed and more air pressure

LIFT THRUST DRAG GRAVITY

less air speed more pressure greater air speed less pressure Spoiler – airfoil reversed less air speed more pressure greater air speed less pressure net force: downward

Racecar less air speed more pressure greater air speed less pressure Spoiler provides better Traction and avoids lift greater air speed less pressure net force: downward

slow air speed fast air speed

Curve Ball

Atomizer – As air passes at top of tube, the pressure decreases and fluid is drawn up the tube.