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Published byJesse Terence Allen Modified over 4 years ago

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**Today’s special ISS tour 1 Notes I HW I due next time Class work time**

Lab next: Buoyant force

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Because the theater seat exerts a supporting force over a larger area, it is more comfortable than the bicycle seat.

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**Pressure is the result of a force distributed over an area.**

The unit of force is the newton (N). The unit of area is the square meter (m2). The SI unit of pressure is the pascal (Pa). A pascal is one newton per square meter (N/m2)

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Pressure If the area of a box touching the ground is 1.5 square meters, and its weight is 2700 newtons, what pressure does the box exert on the ground?

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Pressure If the area of a box touching the ground is 1.5 square meters, and its weight is 2700 newtons, what pressure does the box exert on the ground?

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**A fluid is a substance that assumes the shape of its container.**

Pressure in Fluids A fluid is a substance that assumes the shape of its container. Both liquids and gases are fluids. Water, oil, gasoline, air, and helium are examples of fluids.

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Pressure in Fluids Particles in a liquid are tightly packed together but are able to slide past one another.

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Pressure in Fluids Particles in a gas are far apart and travel in straight lines until they collide with another particle or object.

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Pressure in Fluids Water in a glass is in contact with the walls and bottom of the glass, and it exerts pressure on these surfaces. For a fluid that is not moving, depth and the type of fluid are the two factors that determine the pressure the fluid exerts.

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**Exploring Boiling Points of Chlorocarbons**

Interpreting Tables Which planet listed in the table has the greatest atmospheric pressure?

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**Exploring Boiling Points of Chlorocarbons**

Interpreting Tables Which planet listed in the table has the greatest atmospheric pressure? Answer: Venus, 9120 kPa

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**Exploring Boiling Points of Chlorocarbons**

Interpreting Tables What chemical substance exists in all but one of the atmospheres?

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**Exploring Boiling Points of Chlorocarbons**

Interpreting Tables What chemical substance exists in all but one of the atmospheres? Answer: Nitrogen

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**Exploring Boiling Points of Chlorocarbons**

Converting Units The bar is another unit of pressure (1 bar = kPa). Convert each of the given pressures into bars.

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**Exploring Boiling Points of Chlorocarbons**

Converting Units The bar is another unit of pressure (1 bar = kPa). Convert each of the given pressures into bars. Answer: Mercury, 10–15 bar; Earth, 1 bar; Venus, 90.0 bar; Mars, bar

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**Exploring Boiling Points of Chlorocarbons**

Using Formulas How much force is exerted on a 2.00-square-meter area of Venus’s surface?

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**Exploring Boiling Points of Chlorocarbons**

Using Formulas How much force is exerted on a 2.00-square-meter area of Venus’s surface? Answer: Pressure = Force/Area; Force = Pressure × Area; Force = 9120 kPa × 2.00 m2 = 9.12 × 106 N/m2 × 2.00 m2 = 2.00 × 107 N

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**Exploring Boiling Points of Chlorocarbons**

Predicting On which planet would a balloon filled with a given quantity of helium have the smallest volume?

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**Exploring Boiling Points of Chlorocarbons**

Predicting On which planet would a balloon filled with a given quantity of helium have the smallest volume? Answer: The helium-filled balloon would have the smallest volume on Venus because Venus has the greatest atmospheric pressure.

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Demonstration Recycling the physics way

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Assessment Questions A gymnast standing on one hand (area 0.02 m2) pushes down on the ground with a force of 600 N. How much pressure does the gymnast exert on the ground? 3000 Pa 30,000 Pa 12 Pa 1200 Pa

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Assessment Questions A gymnast standing on one hand (area 0.02 m2) pushes down on the ground with a force of 600 N. How much pressure does the gymnast exert on the ground? 3000 Pa 30,000 Pa 12 Pa 1200 Pa ANS: B

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**The SI unit for pressure, equal to 1 N/m2, is called the**

Assessment Questions The SI unit for pressure, equal to 1 N/m2, is called the atmosphere. foot-pound. pascal. watt.

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**The SI unit for pressure, equal to 1 N/m2, is called the**

Assessment Questions The SI unit for pressure, equal to 1 N/m2, is called the atmosphere. foot-pound. pascal. watt. ANS: C

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**The pressure exerted by a stationary fluid is determined by**

Assessment Questions The pressure exerted by a stationary fluid is determined by the area of surface containing the fluid and the type of fluid. the weight and volume of the fluid. the type of fluid and its depth. the shape of the container and the weight of the fluid.

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**The pressure exerted by a stationary fluid is determined by**

Assessment Questions The pressure exerted by a stationary fluid is determined by the area of surface containing the fluid and the type of fluid. the weight and volume of the fluid. the type of fluid and its depth. the shape of the container and the weight of the fluid. ANS: C

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**Which of the following statements about fluid pressure is false?**

Assessment Questions Which of the following statements about fluid pressure is false? Pressure increases as depth increases. The pressure at a given depth is constant. The pressure in a fluid is exerted downward. Liquids and gases exert pressure.

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**Which of the following statements about fluid pressure is false?**

Assessment Questions Which of the following statements about fluid pressure is false? Pressure increases as depth increases. The pressure at a given depth is constant. The pressure in a fluid is exerted downward. Liquids and gases exert pressure. ANS: C

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Assessment Questions Why do mountain climbers on very high peaks need cylinders of oxygen as they approach the summit? The tops of the mountains extend out of the atmosphere. The pressure of air decreases as altitude increases. Air on the mountaintops is too cold to breathe. Air pressure at high altitudes is too great for normal breathing.

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Assessment Questions Why do mountain climbers on very high peaks need cylinders of oxygen as they approach the summit? The tops of the mountains extend out of the atmosphere. The pressure of air decreases as altitude increases. Air on the mountaintops is too cold to breathe. Air pressure at high altitudes is too great for normal breathing. ANS: B

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**Transmitting Pressure in a Fluid**

Pascal’s Principle The forces exerted against the walls of the container are equal at a given depth. When squeezed, the pressure is transmitted equally throughout the fluid.

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**Transmitting Pressure in a Fluid**

At any given depth, equal pressures act against all points on the inside of the bottle. When the bottle is squeezed, the pressure still increases with depth. The pressure increases equally throughout the water.

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**Transmitting Pressure in a Fluid**

The truck uses hydraulic-powered struts to lift its load. The larger area of the output piston produces the increased force.

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**Bernoulli’s Principle**

Try this simple experiment. Hold a sheet of paper by its top corners. Position the paper directly in front of your mouth. Blow over the top surface of the paper. The far end of the paper lifts upward.

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**Bernoulli’s Principle**

As the air blows across the top of the paper, the pressure exerted by the air decreases. The motionless air below the paper exerts a greater pressure. The difference in pressure forces the paper upward.

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**Bernoulli’s Principle**

Wings and Lift Bernoulli’s principle explains the ability of birds and airplanes to fly. Air traveling over the top of an airplane wing moves faster than the air passing underneath. The pressure difference between the top and the bottom of the wing creates an upward force known as lift.

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**Bernoulli’s Principle**

Air flowing over the top of the wing is diverted up and over the wing’s curved surface.

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**Bernoulli’s Principle**

Spray Bottles Pressure differences between the solution chamber and the moving stream of water draw the solution into the stream.

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Assessment Questions A water balloon can explode if squeezed tightly between two hands. Just prior to exploding, at what point of the balloon is the pressure exerted by the water greatest? It’s greatest at the top of the balloon (point furthest from the ground). It’s greatest at the bottom of the balloon (point nearest the ground). It’s greatest at the points of contact between the balloon and the two hands. The pressure exerted by the water is the same at all points of the balloon.

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Assessment Questions A water balloon can explode if squeezed tightly between two hands. Just prior to exploding, at what point of the balloon is the pressure exerted by the water greatest? It’s greatest at the top of the balloon (point furthest from the ground). It’s greatest at the bottom of the balloon (point nearest the ground). It’s greatest at the points of contact between the balloon and the two hands. The pressure exerted by the water is the same at all points of the balloon. ANS: A

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Assessment Questions A 5-N input force of a hydraulic system corresponds to a 40-N output force. If the area of the small piston is 11 cm2, what is the area of the large piston? 8 cm 255 cm 288 cm 2200 cm2

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Assessment Questions A 5-N input force of a hydraulic system corresponds to a 40-N output force. If the area of the small piston is 11 cm2, what is the area of the large piston? 8 cm 255 cm 288 cm 2200 cm2 ANS: C

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Assessment Questions According to Bernoulli’s principle, as the speed of a moving fluid increases, the pressure within the fluid increases. True False

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Assessment Questions According to Bernoulli’s principle, as the speed of a moving fluid increases, the pressure within the fluid increases. True False ANS: F, decreases

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Today’s special HW check; Q & A Lab: Buoyant force Lab due next time!

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**Today’s special Turn in lab on front table ISS tour 2**

Notes II Buoyancy HW II due next time

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**The forces from pressure acting on the bottom of this golf ball are greater than those on the top.**

This produces a net force—called the buoyant force—that acts upward on the ball.

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Buoyant Force What is the effect of buoyancy on the apparent weight of an object? Buoyancy is the ability of a fluid to exert an upward force on an object placed in it. Buoyancy results in the apparent loss of weight of an object in a fluid.

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**Every object in a fluid experiences buoyancy.**

Buoyant Force Every object in a fluid experiences buoyancy. Water pressure increases with depth. Forces pushing up on the bottom of the object are greater than the forces from pressure pushing down on the top. This upward force, which acts in the opposite direction of gravity, is called the buoyant force.

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**Archeimedes’ Principle**

According to Archimedes’ principle, the buoyant force on an object is equal to the weight of the fluid displaced by the object. A submerged object pushes aside, or displaces, a volume of fluid equal to its own volume. A floating object displaces a volume equal to the volume of the part of the object that is submerged.

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Density and Buoyancy How can you determine if an object will float or sink in a fluid? If an object is less dense than the fluid it is in, it will float. If the object is more dense than the fluid it is in, it will sink. When the buoyant force is equal to the weight, an object floats or is suspended. When the buoyant force is less than the weight, the object sinks.

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Density and Buoyancy Two forces act on every object in a fluid—weight and the buoyant force. The force of gravity, equal to the object’s weight, acts downward on the object. The buoyant force, equal to the weight of the volume of displaced fluid, acts upward on the object.

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**Density and Buoyancy Suspended**

An object that has the same density as the fluid it is submerged in will be suspended (it will float at any level) in the fluid. The buoyant force acting on the suspended object exactly equals the object’s weight. Submarines and some fish are able to suspend themselves in water partly by adjusting their density.

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Density and Buoyancy Sinking When a ship’s weight becomes greater than the buoyant force acting on it, the ship will sink. As a sinking ship takes on water, the ship displaces less water, and the buoyant force decreases.

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Density and Buoyancy Floating A solid piece of steel sinks in water. A heavy steel ship floats because of the shape of its hull. The hull is shaped so that it displaces a large volume of water, creating a large buoyant force.

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**The weight and buoyant force determine if an object sinks or floats.**

Density and Buoyancy The weight and buoyant force determine if an object sinks or floats. Weight Buoyant force

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**The weight and buoyant force determine if an object sinks or floats.**

Density and Buoyancy The weight and buoyant force determine if an object sinks or floats. Weight Weight Buoyant force Buoyant force

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**The weight and buoyant force determine if an object sinks or floats.**

Density and Buoyancy The weight and buoyant force determine if an object sinks or floats. Weight Weight Weight Buoyant force Buoyant force Buoyant force

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**Objects also float more easily in dense fluids.**

Density and Buoyancy Objects also float more easily in dense fluids. The denser the fluid is, the greater is the weight displaced. The greater displaced weight results in a greater buoyant force. This is why it is easier for a person to float in very salty water. The dense salty water produces a larger buoyant force when displaced by the person's body.

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Density and Buoyancy The exposed green and red stripes on the ship’s hull indicate that the ship is riding high in the water. If the cargo ship were completely loaded, it would need to displace more water in order to float.

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Assessment Questions According to Archimedes’ principle, the buoyant force acting on an object is equal to the weight of the object. the pressure exerted by the fluid at the point of contact with the object. the pressure exerted at the bottom of the fluid. the weight of the fluid displaced by the object.

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Assessment Questions According to Archimedes’ principle, the buoyant force acting on an object is equal to the weight of the object. the pressure exerted by the fluid at the point of contact with the object. the pressure exerted at the bottom of the fluid. the weight of the fluid displaced by the object. ANS: D

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Assessment Questions How much fluid is displaced by an object that is floating, partially submerged, in a fluid? a volume of fluid equal to the volume of the object a volume of fluid equal to the volume of the submerged part of the object a mass of fluid equal to the mass of the object a mass of fluid equal to the mass of the submerged part of the object

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Assessment Questions How much fluid is displaced by an object that is floating, partially submerged, in a fluid? a volume of fluid equal to the volume of the object a volume of fluid equal to the volume of the submerged part of the object a mass of fluid equal to the mass of the object a mass of fluid equal to the mass of the submerged part of the object ANS: B

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Assessment Questions An unknown substance is suspended in water. What can be concluded about the substance’s density? The substance’s density is greater than water’s density. The substance’s density is less than water’s density. The substance’s density is equal to water’s density. Nothing can be concluded about the substance’s density.

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Assessment Questions An unknown substance is suspended in water. What can be concluded about the substance’s density? The substance’s density is greater than water’s density. The substance’s density is less than water’s density. The substance’s density is equal to water’s density. Nothing can be concluded about the substance’s density. ANS: C

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Assessment Questions A 10,000-N ship is floating in the Great Salt Lake, whose salty water is denser than pure water. What is the buoyant force acting on the ship? 1000 N 8000 N 10,000 N 12,000 N

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Assessment Questions A 10,000-N ship is floating in the Great Salt Lake, whose salty water is denser than pure water. What is the buoyant force acting on the ship? 1000 N 8000 N 10,000 N 12,000 N ANS: C

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