Fluids

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This text is meant to accompany class discussions. It is not everything there is to know about fluids, hydrostatics, and fluid dynamics. It is meant as a prep for class.
Click for the questions that go with this reading
Pascal's Principal

Pressure is transmitted EQUALLY instantly to all parts of an enclosed container. This principle is employed when every we use machinery to move very heavy loads. To do this we use hydraulic cylinders. Below is an image of a Caterpillar brand tractor. The some of the hydraulic cylinders are circled in red.

Pascal's principal is mechanical advantage for fluids!

This video explaining Pascal's principle can be found on YouTube at https://youtu.be/fpnxo2LFzP4
 

Given the perfect fluid and enough space, you could make a hydraulic system that uses Pascal's principle to lift the Empire State building using your body's weight to lift it.


 

Image from: Cat.com,. ' Cat | 416F Backhoe Loader | Caterpillar'. N. p., 2015. Web. 23 Aug. 2015.

 

Here is what a hydraulic cylinder alone looks like.
Hydraulic Cylinder

Image from: Mobilehydraulictips.com,Mobilehydraulictips.com,. N. p., 2015. Web. 23 Aug. 2015. (http://www.mobilehydraulictips.com/wp-content/uploads/2012/09/Hydraulic-Cylinder-3.jpg)

 

 

Pascal's principal can be used any time you have a closed container where one side is being collapsed, then you can figure out what is happening on the other side, or parts, of the container. Homemade water toys will often use this principle.

"Pascal's Principle" implies

 

Pascals Principle is like mechanical advantage for fluids. This means the force exerted on an opening changes by the ratio of areas. Here's a closer look at the hydraulic arm.

 

There are two openings in this cylinder. The small opening on the right pumping and extracting oil into the chamber with the piston in it and the large opening on the left that presses against the piston's arm. According to Pascal's principle, the pressure at "the large opening," Plarge opening is the same as the pressure at "small opening," Psmall opening.

 

 

This shows that the force at location B in the syringe changes by a factor of the ratio of the areas. When the area gets smaller, the applied force gets smaller compared to the other side. When the area gets the larger, the force gets larger compared to the the other area.

 

Example
  • Question
  • Video Solution

A syringe has a stopper secured to the small end. Your finger applies a force of 60 N to the plunger as shown. How much force is exerted on the stopper if the other measurements are as shown below?

 
Example
  • Question
  • Solution on Notebook Paper
  • Video Solution

A system of two tanks are connected by a skinny pipe and the system is sealed from the outside. Air is pumped into tank “A” on the left. This increases the pressure at opening “A.” A hydraulic fluid is moved into tank “B” and presses up on opening “B.” If a 2550 kg car is to be lifted by the cylinder at opening “B,” then what pressure AND force that must be exerted at opening “A?”

This video can be found on YouTube at https://youtu.be/wJAnfe3mf3E

This video can be found on YouTube at https://youtu.be/hYRiitKPip4


by Tony Wayne ...(If you are a teacher, please feel free to use these resources in your teaching.)

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