2.5 FORCES IN FLUIDS

PASCAL’S BARREL EXPERIMENT Experiment associated with Blaise Pascal A long thin tube placed into a barrel. Water is poured in the top that increases the Hydrostatic Pressure based on elevation and causes the barrel to burst.

HISTORY OF BLAISE PASCAL ( ) French mathematician, physicist, inventor, and writer Mathematics 1642 – invented one of the first two mechanical calculators (Pascaline) Pascals Triangle – presents Binomial coefficients

HISTORY OF BLAISE PASCAL ( ) Worked in the fields of hydrodynamics, hydrostatics and hydraulic fluids Proposed vacuums were possible Worked with barometers – showed how pressure changed by taking a barometer to the top of a bell tower in Paris Invented the hydraulic press and the syringe

Pressure The result of a force distributed over a given area. Equation for Pressure: Pressure = Force / Area Force = Newton’s Area = m 2 Units for pressure = Pascal (Pa) FORCES IN FLUIDS

Example #1 Each tile on the bottom of a swimming pool has an area of 0.50 m 2. The water above each tile exerts a force of 11,000 N on each tile. How much pressure does the water exert on each tile? Pressure = Force / Area Pressure = 11,000 N / 0.50 m 2 Pressure = 22,000 Pascal's

Example #2 The weight of a gallon of milk is about 38 N. If you pour a gallon of milk into a container whose bottom has an area of 0.60 m 2, how much pressure will the milk exert on the bottom of the container? Pressure = Force / Area Pressure = 38 N / 0.60 m 2 Pressure = Pascal's

Two factors that affect fluid pressure: 1.Depth (Remember Pascals Barrel Experiment) 2.Type of fluid FORCES IN FLUIDS

Pascal’s Principle A change in pressure at any point in a fluid is transmitted equally and unchanged in all directions throughout the fluid.

What is a hydraulic system? A device that uses pressurized fluid acting on pistons of different sizes to change a force.

How does a hydraulic system use fluid pressure to do work? An increased output force is produced because a constant pressure is exerted on the larger area of the output piston.

Example

Draw this diagram:

Bernoulli’s Principle As the speed of a fluid increases, the pressure within the fluid decreases. Air always moves from higher pressure to lower pressure

How do we use Bernoulli’s principle to make planes fly (Draw diagram)?

13.1 Assessment 1. What must you know to calculate pressure? Force and Area

13.1 Assessment 2. What is the relationship between depth of water and the pressure it exerts? Water pressure increases as depth increases

13.1 Assessment 3. How is pressure distributed at a given level in a fluid? At an given depth, pressure is constant and exerted equally in all directions.

13.1 Assessment 4. How does the pressure exerted by the atmosphere change as altitude increases? Pressure decreases as altitude increases

13.1 Assessment 5. Describe Pascal's Principle A change in pressure at any point in a fluid is transmitted equally and unchanged in all directions throughout the fluid.

13.1 Assessment 6. How are fluid speed and fluid pressure related. As the speed of a fluid increases, the pressure within the fluid decreases.

13.1 Assessment 7. How does an airplane wing produce lift? Bernoulli’s Principle: Air traveling over the top of the wing produces an area of low pressure. High Pressure is below the wing (high pressure goes to low pressure) and produces lift.

13.1 Assessment Problem #1: The weight of the gasoline in a 55 gallon drum creates a force of 1,456 Newton’s. The area of the bottom of the drum is 0.80 m 2. How much pressure does the gasoline exert on the bottom of the drum?

13.1 Assessment Problem #2: A company makes garden statues by pouring concrete into a mold. The amount used to make a statue if a deer weighs 3,600 N. If the base of the deer statue is 0.60 m long and 0.40 meters wide, how much pressure will the statue exert on a the ground? (Hint: Area is equal to length times width)

13.1 Assessment Problem #3: A book with a weight of 12 N rests on its back cover. If the books cover measures 0.21 m by 0.28 m, how much pressure does the book exert?