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**Chapter Preview Questions**

1. Which of the following is an example of a force? a. water b. other fluids c. gravity d. mass

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**Chapter Preview Questions**

1. Which of the following is an example of a force? a. water b. other fluids c. gravity d. mass

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**Chapter Preview Questions**

2. A fluid can be a. a gas only. b. a liquid only. c. a solid or a gas. d. a liquid or a gas.

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**Chapter Preview Questions**

2. A fluid can be a. a gas only. b. a liquid only. c. a solid or a gas. d. a liquid or a gas.

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**Chapter Preview Questions**

3. The velocity of an object is a. its standard reference point. b. the rate of change of its position. c. the process of speeding it up. d. its change in direction.

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**Chapter Preview Questions**

3. The velocity of an object is a. its standard reference point. b. the rate of change of its position. c. the process of speeding it up. d. its change in direction.

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**Chapter Preview Questions**

4. Earth’s gravity pulls you down with a force a. greater than your weight. b. the size of your feet. c. equal to your weight. d. half your weight.

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**Chapter Preview Questions**

4. Earth’s gravity pulls you down with a force a. greater than your weight. b. the size of your feet. c. equal to your weight. d. half your weight.

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Section 1:Pressure Standard 8.8.d Students know how to predict whether an object will float or sink. Standard 8.9.f Apply simple mathematical relationships to determine a missing quantity in a mathematic expression, given the two remaining terms Force = pressure x area

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**What Is Pressure? What does pressure depend on?**

The amount of pressure you exert depends on the area over which you exert a force.

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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 cm2.

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Area Practice Problem Which has a greater area: a rectangle that is 4 cm X 20 cm or a square that is 10 cm X 10 cm? The square has the greater area. 4 cm X 20 cm = 80 cm2 10 cm X 10 cm = 100 cm2

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Calculating Pressure How is pressure calculated? Example: Calculate the pressure produced by a force of 800 N acting on an area of 2.0 square meters. Pressure = Force / Area Pressure is measured in an SI unit called a pascal (Pa): 1 N/square meter = 1 Pa. P = F/A P= (800N) / (2.0 square meters) P = 400 N / square meter = 400 Pa

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Calculating Pressure The SI unit for pressure, the pascal, is named for French mathematician Blaise Pascal. The SI unit for force, the newton, is named for English physicist Sir Isaac Newton.

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Math Practice Calculate the pressure produced by a force of 450 N on an area of 3 square meters. P = F/A P = (450 N) / (3 square meters) P = 150 N / square meter = 150 Pa What is the pressure on 2.5 by 3 meter area being acted upon by a force of 6000 N? P = 6000 N / (2.5)(3) square meters P = 6000 N / 7.5 square meters P = 800 Pa

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**Calculating Force from Pressure**

How is force calculated from pressure? Force is expressed in Newtons (N) Force = Pressure x Area Example The pressure of a gas contained in a cylinder with a movable piston is 300 Pa. The area of the piston is 0.5 square meters. Calculate the force that is exerted on the piston. F = P x A F = (300 Pa) x 0.5 m2 F = 150 N

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Math Practice The pressure of a gas contained in a cylinder with a movable piston is 700 Pa. The area of the piston is 0.2 square meters. What is the force that is exerted on the piston? F = P x A F = (700 Pa) (0.2 square meters) F = 140 N

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**Fluid Pressure How do fluids exert pressure?**

All of the forces exerted by the individual particles in a fluid combine to make up the pressure exerted by the fluid.

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**Fluid Pressure Air pressure Balanced pressure**

Air is a mixture of gases that make up Earth’s atmosphere. These gases press down on everything on Earth’s surface. Air exerts pressure because it has mass. Balanced pressure explains why the tremendous air pressure pushing on you from all sides does not crush you. Pressure from fluids inside your body balances the air pressure outside your body.

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**Variations in Fluid Pressure**

How does fluid pressure change with elevation and depth? Atmospheric pressure decreases as your elevation increases. You can measure atmospheric pressure with an instrument called a barometer. Water pressure increases as depth increases.

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**Variations in Fluid Pressure**

As your elevation increases, atmospheric pressure decreases.

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**Variations in Fluid Pressure**

Water pressure increases as depth increases.

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Section 1 Quick Quiz Snowshoes enable a person to walk on deep snow because the snowshoes decrease the person’s weight on the snow. increase the pressure on the snow. increase the buoyancy of the person. increase the area over which the person’s weight is distributed. Answer – D - increase the area over which the person’s weight is distributed.

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**Section 1 Quick Quiz A unit of pressure is called a pound. meter.**

pascal. bernoulli. Answer – C - pascal

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**Section 1 Quick Quiz Pressure can be measured in units of**

newtons per square meter. newtons per cubic centimeter. newtons per centimeter. newtons. Answer – A – newtons per square meter

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Section 1 Quick Quiz Air pressure exerted equally on an object from different directions is gravitational pressure. balanced pressure. constant pressure. fluid pressure. Answer – B – balanced pressure

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Section 1 Quick Quiz Given that the air pressure outside your body is so great, why aren’t you crushed? Earth’s gravity cancels out the air pressure. Inertia changes the pressure before it comes into contact with you. Human skin is extremely strong. Pressure inside your body balances the air pressure outside your body. Answer – D - Pressure inside your body balances the air pressure outside your body.

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**Section 1 Quick Quiz Air pressure decreases as elevation increases.**

velocity increases. gravity increases. acceleration decreases. Answer – A – elevation increases

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**Section 1 Quick Quiz Water pressure increases as**

acceleration increases. gravity decreases. depth increases. force decreases. Answer – C – depth increases

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**Section 1 Quick Quiz A barometer is used to measure pressure**

in the atmosphere. in hydraulic systems. under a snowshoe. under water. Answer – A – in the atmosphere

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**Section 2: Floating and Sinking**

Standard 8.8.c Students know the buoyant force on an object in a fluid is an upward force equal to the weight of the fluid the object displaced. Standard 8.8.d Students know how to predict whether an object will float or sink.

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**Calculating Density How is density calculated? Example:**

The density of a substance is its mass per unit of volume. Density = Mass Volume A sample of liquid has a mass of 24 g and a volume of 16 mL. What is its density? Density = Mass = 24 g = 1.5 g/mL Volume 16 mL

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**Calculating Density Practice Problem**

A piece of metal has a mass of 43.5 g and a volume of 15 cm3. What is its density? 2.9 g/cm3

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Calculating Density A block has a mass of 320 g and a volume of 80 cubic centimeters. What is its density? 4 g / cubic centimeter An orange has a mass of 250 g and a volume of 750 mL. What is its density? .33 g / mL

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**Section 2: Floating and Sinking**

How is density calculated? How can you predict whether an object will float or sink in a fluid? What is the effect of the buoyant force?

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Density Changes in density cause a submarine to dive, rise, or float.

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Density Changes in density cause a submarine to dive, rise, or float.

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Density Changes in density cause a submarine to dive, rise, or float.

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Buoyancy The pressure on the bottom of a submerged object is greater than the pressure on the top. The result is a net force in the upward direction.

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Buoyancy The buoyant force works opposite the weight of an object.

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Buoyancy Archimedes’ principle states that the buoyant force acting on a submerged object is equal to the weight of the fluid the object displaces.

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Buoyancy A solid block of steel sinks in water. A steel ship with the same weight floats on the surface.

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Section 2 Quick Quiz Which of the following is true of the buoyant force? It acts in the downward direction. It makes an object feel heavier. It acts with the force of gravity. It acts in the upward direction. Answer – D – It acts in the upward direction

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Section 2 Quick Quiz If an object floats, the volume of displaced water is equal to the volume of exactly half of the object. the entire object. the portion of the object that is submerged. the portion of the object that is above water. Answer – C – the portion of the object that is submerged

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Section 2 Quick Quiz When water fills a submarine’s flotation tanks, the overall density of the submarine stays the same. decreases. reduces the buoyant force. increases. Answer – D - increases

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Section 2 Quick Quiz An object that is more dense than the fluid in which it is immersed will rise. sink. sink at first, then rise slowly. neither rise nor sink. Answer – B - sink

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**Section 2 Quick Quiz Which of these substances is the LEAST dense?**

rubber mercury copper wood Answer – D - wood

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Section 2 Quick Quiz What scientific rule states that the buoyant force on an object is equal to the weight of the fluid displaced by the object? Archimedes’ principle Newton’s third law of motion Bernoulli’s principle Pascal’s principle Answer – A – Archimedes’ principle

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**Section 3: Pascal’s Principle**

Standard 8.8.c Students know the buoyant force on an object in a fluid is an upward force equal to the weight of the fluid the object has displaced.

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**Section 3: Pascal’s Principle**

What does Pascal’s principle say about change in fluid pressure? How does a hydraulic system work?

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**Transmitting Pressure in a Fluid**

When force is applied to a confined fluid, the change in pressure is transmitted equally to all parts of the fluid.

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Hydraulic Devices In a hydraulic device, a force applied to one piston increases the fluid pressure equally throughout the fluid.

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Hydraulic Devices By changing the size of the pistons, the force can be multiplied.

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**Comparing Hydraulic Lifts**

In a hydraulic device, 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.

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**Comparing Hydraulic Lifts**

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. Lift A: 4,000 N; lift B: 2,000 N

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**Comparing Hydraulic Lifts**

Reading Graphs: For Lift A, how much force must be applied to lift a 12,000-N object? 3,000 N

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**Comparing Hydraulic Lifts**

Interpreting Data: By how much is the applied force multiplied for Lift A? Lift B? Lift A: applied force is multiplied by four; lift B: applied force is multiplied by two.

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**Comparing Hydraulic Lifts**

Interpreting Data: What does the slope of each line represent? The slope gives the ratio of the lifting force to the applied force. The greater the slope, the more the lift multiplies force.

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**Comparing Hydraulic Lifts**

Drawing Conclusions: Which lift would you choose if you wanted to lift a weight of 4,000 N? Explain. Lift A, because it multiplies force more than lift B.

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Hydraulic Brakes The hydraulic brake system of a car multiplies the force exerted on the brake pedal.

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**Section 3 Quick Quiz The braking system on a car is an example of**

Bernoulli’s principle. Newton’s third law of motion. a hydraulic system. buoyancy. Answer – C – a hydraulic system.

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Section 3 Quick Quiz Which type of substance does Pascal’s principle deal with? fluids powders metals solids Answer – A - fluids

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**Section 3 Quick Quiz One application of Pascal’s principle is**

the flight of an airplane. a speedboat’s bottom slapping against the waves. a hydraulic car lift. the buoyancy shown by ducks and other waterfowl. Answer – C – a hydraulic car lift

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**Section 3 Quick Quiz What does a hydraulic system do? multiply force**

reduce inertia increase velocity decrease pressure Answer – A – multiply force

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**Section 4: Bernoulli’s Principle**

Standard 8.2.e Students know that when the forces on an object are unbalanced, the object will change its velocity (that is, it will speed up, slow down, or change direction).

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**Section 4: Bernoulli’s Principle**

How is fluid pressure related to the motion of a fluid? What are some applications of Bernoulli’s principle?

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**Bernoulli’s Principle**

Bernoulli’s principle states that as the speed of a moving fluid increases, the pressure exerted by the fluid decreases.

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**Applying Bernoulli’s Principle**

Bernoulli’s principle helps explain how planes fly.

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**Applying Bernoulli’s Principle**

An atomizer is an application of Bernoulli’s principle.

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**Applying Bernoulli’s Principle**

Thanks in part to Bernoulli's principle, you can enjoy an evening by a warm fireplace without the room filling up with smoke.

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**Applying Bernoulli’s Principle**

Like an airplane wing, a flying disk uses a curved upper surface to create lift.

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Section 4 Quick Quiz What scientific rule states that the pressure exerted by a moving stream of fluid is less than the pressure of the surrounding fluid? Newton’s third law of motion Bernoulli’s principle Archimedes’ principle Pascal’s principle Answer – B – Bernoulli’s principle

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**Section 4 Quick Quiz Smoke rises up a chimney partly because of**

Bernoulli’s principle Archimedes’ principle Newton’s third law of motion Pascal’s principle Answer – A – Bernoulli’s principle

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