# How is pressure calculated? - PowerPoint PPT Presentation

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Because the theater seat exerts a supporting force over a larger area, it is more comfortable than the bicycle seat. Pressure. How is pressure calculated?. To calculate pressure, divide the force by the area over which the force acts. Pressure.

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How is pressure calculated?

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#### Presentation Transcript

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

Pressure

How is pressure calculated?

To calculate pressure, divide the force by the area over which the force acts.

Pressure

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)

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?

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?

Pressure in Fluids

How does water pressure change with depth?

How is pressure distributed at a given level in a fluid?

Pressure in Fluids

Water pressure increases as depth increases. The pressure in a fluid at any given depth is constant, and it is exerted equally in all directions.

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.

Pressure in Fluids

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

Pressure in Fluids

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

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.

Pressure in Fluids

Each vase holds a different amount of liquid. The liquid levels are all the same because pressure depends on depth, not amount.

Planetary Atmospheres

The layer of gases surrounding a planet is known as its atmosphere. All of the planets in our solar system have some form of atmosphere. The weight of an atmosphere creates atmospheric pressure at the planet’s surface.

Exploring Boiling Points of Chlorocarbons

• Interpreting TablesWhich planet listed in the table has the greatest atmospheric pressure?

Exploring Boiling Points of Chlorocarbons

• Interpreting TablesWhich planet listed in the table has the greatest atmospheric pressure?

Exploring Boiling Points of Chlorocarbons

• Interpreting TablesWhat chemical substance exists in all but one of the atmospheres?

Exploring Boiling Points of Chlorocarbons

• Interpreting TablesWhat chemical substance exists in all but one of the atmospheres?

Exploring Boiling Points of Chlorocarbons

• Converting UnitsThe bar is another unit of pressure (1 bar = 101.3 kPa). Convert each of the given pressures into bars.

Exploring Boiling Points of Chlorocarbons

• Converting UnitsThe bar is another unit of pressure (1 bar = 101.3 kPa). Convert each of the given pressures into bars.

Answer: Mercury, 10–15 bar; Earth, 1 bar; Venus, 90.0 bar; Mars, 0.0070 bar

Exploring Boiling Points of Chlorocarbons

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

Exploring Boiling Points of Chlorocarbons

• Using FormulasHow 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

Exploring Boiling Points of Chlorocarbons

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

Exploring Boiling Points of Chlorocarbons

• PredictingOn 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.

Air Pressure and the Atmosphere

How does air pressure change with altitude?

Air pressure decreases as the altitude increases.

Air Pressure and the Atmosphere

Earth’s atmosphere exerts pressure of about 101 kPa at sea level. Why aren't you crushed by air pressure?

Air Pressure and the Atmosphere

Earth’s atmosphere exerts pressure of about 101 kPa at sea level. Why aren't you crushed by air pressure?

The pressure inside your body balances the air pressure outside. The balanced forces cancel, resulting in a net force of zero.

Air Pressure and the Atmosphere

A can containing a small amount of water is heated until the water boils. Then the can is capped. As the can cools, the pressure inside the can becomes less than the pressure outside the can. The difference in pressure crushes the can.

Air Pressure and the Atmosphere

A can containing a small amount of water is heated until the water boils. Then the can is capped. As the can cools, the pressure inside the can becomes less than the pressure outside the can. The difference in pressure crushes the can.

Air Pressure and the Atmosphere

A can containing a small amount of water is heated until the water boils. Then the can is capped. As the can cools, the pressure inside the can becomes less than the pressure outside the can. The difference in pressure crushes the can.

Air Pressure and the Atmosphere

A can containing a small amount of water is heated until the water boils. Then the can is capped. As the can cools, the pressure inside the can becomes less than the pressure outside the can. The difference in pressure crushes the can.

• 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

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 PaANS:B

Assessment Questions

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

• atmosphere.

• foot-pound.

• pascal.

• watt.

Assessment Questions

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

• atmosphere.

• foot-pound.

• pascal.

• watt.ANS:C

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.

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

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.

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

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.

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

Assessment Questions