Forces in Fluids Pressure Floating and Sinking Pascal’s Principle Bernoulli’s Principle Table of Contents

Forces in Fluids Pressure - Book M – Ch 3.1 (pgs ) Pressure – force exerted over an area Pressure decreases as the area over which a force distributed increases. - Pressure

Forces in Fluids - Pressure Pressure - Book M – Ch 3.1 (pgs ) Pressure decreases as the area over which a force is distributed increases. Let’s Practice!

Forces in Fluids 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 cm 2. - Pressure

Forces in Fluids Area Practice Problem Which has a greater area: a rectangle that is 5 cm X 20 cm or a square that is 10 cm X 10 cm? Both have the same area, 100 cm 2. 5 cm X 20 cm = 100 cm 2 10 cm X 10 cm = 100 cm 2 - Pressure

Forces in Fluids Book M – Ch 3.1 (pgs ) Pressure is equal to the force exerted on a surface divided by the total area over which the force is exerted. Force is measured in newtons (N). Area is measured in square meters (m 2 ). The SI unit of pressure is the newton per square meter (N/m 2 ). This unit of pressure is also called the pascal 1 N/m 2 = 1Pa - Pressure

Forces in Fluids Pressure - Book M – Ch 3.1 (pgs ) Fluid - a material that can easily flow. As a result, a fluid can change shape. As each particle in a fluid collides with a surface, it exerts a force on the surface. All of the forces exerted by the individual particles in a fluid combine to make up the pressure exerted by the fluid. - Pressure

Forces in Fluids Pressure - Book M – Ch 3.1 (pgs ) Air pressure (atmospheric pressure) – caused by the force of gases in our atmosphere which are pulled to the earth by gravity Atmospheric gases have a mass of 1 kg per cubic meter We don’t feel this pressure because In a stationary fluid, pressure at a given point is exerted equally in all directions. - Pressure

Forces in Fluids - Pressure Pressure - Book M – Ch 3.1 (pgs ) As your elevation increases, atmospheric pressure decreases. As air pressure outside your body changes, the air pressure inside adjusts slowly.

Forces in Fluids - Pressure Pressure - Book M – Ch 3.1 (pgs ) For a time air pressure behind your eardrums is greater than it is in the air outside. When the body releases this pressure it “pops”

Forces in Fluids - Pressure Pressure - Book M – Ch 3.1 (pgs ) Similarly, as the depth of water increases the pressure increases.

Forces in Fluids Links on Fluids and Pressure Click the SciLinks button for links on fluids and pressure. - Pressure

Forces in Fluids - Floating and Sinking Floating/Sinking - Book M – Ch 3.2 (pgs ) Buoyant force - the upward force exerted by a fluid on a submerged object. Occurs when the pressure on the bottom of a submerged object is greater than the pressure on the top. Results in a net force in the upward direction.

Forces in Fluids - Floating and Sinking Floating/Sinking - Book M – Ch 3.2 (pgs ) The buoyant force acts in the direction opposite to the force of gravity, so it makes an object feel lighter.

Forces in Fluids - Floating and Sinking Floating/Sinking - Book M – Ch 3.2 (pgs ) Archimedes’ principle - states that the buoyant force acting on a submerged object is equal to the weight of the fluid the object displaces.

Forces in Fluids - Floating and Sinking Floating/Sinking - Book M – Ch 3.2 (pgs ) Therefore the larger the volume (space) an object takes up, the greater the buoyant force (upward force). Ex: a solid block of steel sinks while a steel ship with the same weight floats.

Forces in Fluids Floating/Sinking - Book M – Ch 3.2 (pgs ) The density of a substance is its mass per unit volume. By comparing densities, you can predict whether an object will float or sink in a fluid. An object that is denser than the fluid in which it is immersed sinks. An object that is less dense than the fluid in which it is immersed floats to the surface - Floating and Sinking

Forces in Fluids - Floating and Sinking Floating/Sinking - Book M – Ch 3.2 (pgs ) Changes in density cause a submarine to dive, rise, or float.

Forces in Fluids Relating Cause and Effect Object sinks. Weight is greater than buoyant force. Object is denser than fluid. Object takes on mass and becomes denser than fluid. Object is compressed and becomes denser than fluid. - Floating and Sinking Effect Causes

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

Forces in Fluids - Pascal’s Principle Pascal’s principle - Book M – Ch 3.3 (pgs ) Pascal’s principle - The rule that when force is applied to a confined fluid, the increase in pressure is transmitted equally to all parts of the fluid.

Forces in Fluids - Pascal’s Principle Pascal’s principle - Book M – Ch 3.3 (pgs ) A hydraulic device is operated by the movement and force of a fluid. In a hydraulic device, a force applied to one piston increases the fluid pressure equally throughout the fluid.

Forces in Fluids - Pascal’s Principle Pascal’s principle - Book M – Ch 3.3 (pgs ) By changing the size of the pistons, the force can be multiplied.

Forces in Fluids - Pascal’s Principle Pascal’s principle - Book M – Ch 3.3 (pgs ) The hydraulic brake system of a car multiplies the force exerted on the brake pedal. Hydraulic system – a system that multiplies force by transmitting pressure from a small surface area through a confined fluid to a larger surface area. Hydraulic lift systems are used to: raise cars off the lift the heavy ladder on a fire truck used to operate heavy construction equipment like dump trucks, backhoes, snowplows, and cranes.

Forces in Fluids Graphic Organizer How a Hydraulic Device Works Pressure in a confined fluid is increased. Force is applied to a small piston. The pressure is transmitted equally throughout the fluid. The confined fluid presses on a piston with a larger surface area. The original force is multiplied. Comparing Lifts

Forces in Fluids Comparing Hydraulic Lifts In the hydraulic device in Figure 15, a force applied to the piston on the left produces a lifting force in the piston on the right. The graph shows the relationship between the applied force and the lifting force for two hydraulic lifts. - Pascal’s Principle

Forces in Fluids Comparing Hydraulic Lifts Lift A: 4,000 N; lift B: 2,000 N Reading Graphs: Suppose a force of 1,000 N is applied to both lifts. Use the graph to determine the lifting force of each lift. - Pascal’s Principle

Forces in Fluids Comparing Hydraulic Lifts 3,000 N Reading Graphs: For Lift A, how much force must be applied to lift a 12,000-N object? - Pascal’s Principle

Forces in Fluids Comparing Hydraulic Lifts Lift A: applied force is multiplied by four; lift B: applied force is multiplied by two. Interpreting Data: By how much is the applied force multiplied for each lift? - Pascal’s Principle

Forces in Fluids Comparing Hydraulic Lifts The slope gives the ratio of the lifting force to the applied force. The greater the slope, the more the lift multiplies force. Interpreting Data: What can you learn from the slope of the line for each lift? - Pascal’s Principle

Forces in Fluids Comparing Hydraulic Lifts Lift A, because it multiplies force more than lift B. Drawing Conclusions: Which lift would you choose if you wanted to produce the greater lifting force? - Pascal’s Principle

Forces in Fluids Hydraulic Systems Activity Click the Active Art button to open a browser window and access Active Art about hydraulic systems. - Pascal’s Principle

Forces in Fluids - Bernoulli’s Principle Book M – Ch 3 Sec 4 (pgs ) Bernoulli’s principle - the rule that a stream of fast-moving fluid exerts less pressure than the surrounding fluid.

Forces in Fluids - Bernoulli’s Principle Book M – Ch 3 Sec 4 (pgs ) Bernoulli’s principle helps explain how planes fly. Air moving over the curved top part of the wing moves faster than the air on the bottom flat part of the wing.

Forces in Fluids - Bernoulli’s Principle Book M – Ch 3 Sec 4 (pgs ) Applications of Bernoulli’s Principle An atomizer is an application of Bernoulli’s principle.

Forces in Fluids - Bernoulli’s Principle Book M – Ch 3 Sec 4 (pgs ) Thanks in part to Bernoulli's principle, you can enjoy an evening by a warm fireplace without the room filling up with smoke.

Forces in Fluids - Bernoulli’s Principle Book M – Ch 3 Sec 4 (pgs ) Like an airplane wing, a flying disk uses a curved upper surface to create lift.

Forces in Fluids Links on Bernoulli’s Principle Click the SciLinks button for links on Bernoulli’s principle. - Bernoulli’s Principle