Fluid Technology Foundations of Technology Fluid Technology © 2013 International Technology and Engineering Educators Association STEM  Center for Teaching and Learning™ Foundations of Technology Teacher Resource – Unit 2 Lesson 6

The BIG Idea Big Idea: Fluid technology c ombines mechanics with the omni- directional nature of fluids. © 2013 International Technology and Engineering Educators Association STEM  Center for Teaching and Learning™ Foundations of Technology

Fluids Fluids have a loose molecular structure so that they flow and take the shape of their confining container They may be gases Controlling gases under pressure is called pneumatics They may be liquids Controlling liquids under pressure is called hydraulics © 2013 International Technology and Engineering Educators Association STEM  Center for Teaching and Learning™ Foundations of Technology

Pressure A fluid exerts a force equally to all inside surfaces of the container holding it Pressure is measured as a force distributed over a specific area For example: pounds per square inch © 2013 International Technology and Engineering Educators Association STEM  Center for Teaching and Learning™ Foundations of Technology force area

Pressure: Force/Area Pressure is caused by the cumulative force of random molecules of the fluid striking the inside surface of the container. To see how volume and temperature affect the pressure of a contained gas visit this link: PHET Gas Properties Simulator. PHET Gas Properties Simulator © 2013 International Technology and Engineering Educators Association STEM  Center for Teaching and Learning™ Foundations of Technology

Hydraulics Liquids do not compress That makes hydraulics very useful in efficiently transmitting forces © 2013 International Technology and Engineering Educators Association STEM  Center for Teaching and Learning™ Foundations of Technology

Pascal’s Law Pascal experimented with fluids during the renaissance Pascal’s Law states that the pressure at any point in a body of fluid is the same in every direction, exerting equal force on equal areas. So: the pressure is the same, and any change in the pressure at one point in a confined fluid will create an equal change everywhere in the confining vessel. © 2013 International Technology and Engineering Educators Association STEM  Center for Teaching and Learning™ Foundations of Technology

Hydraulic Cylinders © 2013 International Technology and Engineering Educators Association STEM  Center for Teaching and Learning™ Foundations of Technology These 2 fluid filled cylinders connected by a hose represent 1 fluid container. The piston inside each cylinder can slide forcing some fluid from one to the other, pushing the piston and solid rod outward. Because it is one container, Pascal’s Law will apply.

Hydraulic Cylinders © 2013 International Technology and Engineering Educators Association STEM  Center for Teaching and Learning™ Foundations of Technology If we apply 5 pounds of force downward on the top piston rod 5 pounds of force should push out on the lower piston rod. This is because the increased pressure created by the force in the top cylinder will be transmitted equally to the bottom cylinder. 5 lb weight 5 lbs. of force

Hydraulic Cylinders © 2013 International Technology and Engineering Educators Association STEM  Center for Teaching and Learning™ Foundations of Technology This transmission of force will work with a flexible or rigid hose of almost any reasonable length. Extremely small or long connecting hoses will create efficiency robbing molecular friction.

Fluid Mechanical Advantage © 2013 International Technology and Engineering Educators Association STEM  Center for Teaching and Learning™ Foundations of Technology If we vary the size of the piston from one side of the hydraulic system to the other we can easily create tremendous mechanical advantage

Fluid Mechanical Advantage © 2013 International Technology and Engineering Educators Association STEM  Center for Teaching and Learning™ Foundations of Technology That’s because force is only one factor of pressure – area is the other Remember that pressure is force divided by area, and Pascal’s Law states that the pressure is the same in both cylinders

Fluid Mechanical Advantage © 2013 International Technology and Engineering Educators Association STEM  Center for Teaching and Learning™ Foundations of Technology But the area that the pressure pushes against is different in these cylinders Example: if the larger cylinder’s piston surface is 5 times that of the smaller cylinder the resulting force will be 5 times greater

The Math © 2013 International Technology and Engineering Educators Association STEM  Center for Teaching and Learning™ Foundations of Technology Pascal said the pressure in the input cylinder = the pressure in the output cylinder And we know pressure is force / area, then Force in / area in = force out / area out Assume that the input piston area is 1 in 2 and the output piston area is 5 in 2 And assume we apply 2 lbs. of force to the input cylinder’s piston rod 2 lbs./1in 2 = force out/5 in 2 force out = ( 2 lbs./1in 2 ) x 5 in 2 force out = 10 lbs. Input cylinder piston area 1 square inch Output cylinder piston area 5 square inches 2 lbs. force in 10 lbs. force out

Hydraulics For a more complete explanation of hydraulics, please visit this link: /backhoe/intro.html /backhoe/intro.html © 2013 International Technology and Engineering Educators Association STEM  Center for Teaching and Learning™ Foundations of Technology

Using Fluid Technology These fluid technology principles are applied to many engineering solutions from backhoes to elevators and liftgates. © 2013 International Technology and Engineering Educators Association STEM  Center for Teaching and Learning™ Foundations of Technology