# Section 2 Properties of Fluids

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Section 2 Properties of Fluids

What You’ll Learn Explain Archimedes’ Principle
Explain Pascal’s Principle Explain Bernoulli’s principle and explain how we use it

How do ships float? Buoyancy is the ability of a fluid (liquid or gas) to exert an upward force on an object that is immersed in it. Buoyant force = object’s weight  object floats Buoyant force < object’s weight  object sinks Ships like floating cities Able to float bc a greater force is pushing up on the ship that opposes the weight force of the the ship pushing down

Archimedes’ Principle
Who? 3rd century BC Greek mathematician who made a discovery about buoyancy Discovered? Found that the buoyant force on an object is equal to the weight of the fluid displaced by the object King Hiero had commissioned a new royal crown for which he provided solid gold to the goldsmith. When the crown arrived, King Hiero was suspicious that the goldsmith only used some of the gold, kept the rest for himself and added silver to make the crown the correct weight. Archimedes was asked to determine whether or not the crown was pure gold without harming it in the process. Archimedes was perplexed but found inspiration while taking a bath. He noticed that the full bath overflowed when he lowered himself into it, and suddenly realized that he could measure the crown's volume by the amount of water it displaced. He knew that since he could measure the crown's volume, all he had to do was discover its weight in order to calculate its density and hence its purity. Archimedes was so exuberant about his discovery that he ran down the streets of Syracuse naked shouting, “Eureka!” which meant “I've found it!” in Greek.

EXAMPLE FLOATS Place wood block in water
block will push water out of the way as it begins to sink until the weight of the water displaced = the block’s weight RESULT: buoyant force = weight of the block FLOATS

Why do rocks sink? A. bc weight of rock is greater than the buoyant force
Why do tennis balls float? A. bc buoyant force of water is greater than the weight of the ball

Would a steel block and wood block that are both the same volume float?
Steel Block vs. Wood Block Both displace same volume buoyant force is same BUT steel sinks and wood floats- WHAT’S THE DEAL?? Density = mass / volume Now suppose you formed the steel block in the shape of a hull filled with air. Now the same mass takes up a larger volume. The overall density of the steel boat and air is less than the density of water. = Boat floats Mass Volume Density Sink or Float? Steel 24 g 8 cm3 Wood 4 g

Pascal’s Principle Pressure- def. the force exerted per unit area
Pressure (N/m2) = Force (N) / Area (m2) Who? Blaise Pascal ( ) French scientist discovered the useful property of fluids Principle? Pressure applied to a fluid is transmitted throughout the fluid. Ex: Squeeze one end of a toothpaste tube, toothpaste emerges from the other end. The pressure has been transmitted through the fluid toothpaste. Ex: Hydraulic machines in auto repair shops Fig 15 If you are underwater, you can feel the pressure of the water all around you. Earth’s atmosphere is a fluid that exerts a pressure all around you

Bernoulli’s Principle
Who? Daniel Bernoulli ( ) Swiss scientist who studied the properties of moving fluids such as water and air Principle? As the velocity of fluid increases, the pressure exerted by the fluid decreases. Demo Bernoulli’s principle Ex: principle used when designing aircraft wings and hose-end sprayer (fig 17)

Fluid Flow Viscosity – def. the resistance to flow by a fluid
Ex: cold syrup flows slow= high viscosity; heated syrup flows faster= low viscosity Viscosity decreases as temperature increases

Homework Section Review pg 489 #1-7