GasesGases& Plasmas& Plasmas

The AtmosphereThe Atmosphere

AtmosphereAtmosphere

• Unlike water – Density of the atmosphere is Unlike water – Density of the atmosphere is depth-dependentdepth-dependent

• If you have a 30 km tall bamboo pole of cross If you have a 30 km tall bamboo pole of cross section 1 sq cm – the mass of air in it would section 1 sq cm – the mass of air in it would be about 1 kg.be about 1 kg.

• This weight of the air is source of atmospheric This weight of the air is source of atmospheric pressure which is due to 1 kg/sq cm at sea pressure which is due to 1 kg/sq cm at sea levellevel

• A 30 km tall sewer pipe of cross section 1 sq A 30 km tall sewer pipe of cross section 1 sq meter has about 10meter has about 1055 Newtons of weight. Newtons of weight.

AtmosphereAtmosphere

• Dry air at 20Dry air at 20oo C has a density of 1.21 kg/m C has a density of 1.21 kg/m33 which is about 2 ¾ lbs. which is about 2 ¾ lbs.

• What weighs more, the air in a frig or a grapefruit? What weighs more, the air in a frig or a grapefruit?

BarometersBarometers

• Need 10.3 meters of water in a pipe to balance atmosphereNeed 10.3 meters of water in a pipe to balance atmosphere

(depends on atmospheric pressure).(depends on atmospheric pressure).

• Turn long pipe of water into a bucket of water and water level in Turn long pipe of water into a bucket of water and water level in pipe will be 10.3 M with vacuum above water in pipe.pipe will be 10.3 M with vacuum above water in pipe.

BarometersBarometers

• What is max height you can drink water What is max height you can drink water through a straw?through a straw?

• What is the deepest well that you can What is the deepest well that you can pump water with a hand pump?pump water with a hand pump?

• Mercury is 13.6 times as dense as water Mercury is 13.6 times as dense as water and needs 76 cm to balance atmosphere and needs 76 cm to balance atmosphere in a pipe.in a pipe.

Boyle’s LawBoyle’s Law

PP11VV11 = P = P22VV22

• Holds for constant temperatureHolds for constant temperature

• Pressure is proportional to density – when volume is decreased, Pressure is proportional to density – when volume is decreased, density and pressure increasedensity and pressure increase

• Double pressure by decreasing volume by halfDouble pressure by decreasing volume by half

Boyle’s LawBoyle’s Law

PP11VV11 = P = P22VV22

• Atmospheric pressure halves every 6 Km you go up.Atmospheric pressure halves every 6 Km you go up.

• What will happen to the volume of a balloon that rises 6 Km.What will happen to the volume of a balloon that rises 6 Km.

• What happens to the density? What happens to the density?

• What happens if a Scuba Diver 10.3 M deep holds their breath and What happens if a Scuba Diver 10.3 M deep holds their breath and swims to the surface?swims to the surface?

Archimedes’ PrincipleArchimedes’ Principle

• An immersed body is buoyed up by a force equal to the weight of the An immersed body is buoyed up by a force equal to the weight of the fluid it displaces. fluid it displaces.

– Is valid for gasses as well as liquids!

– Objects weigh more in a vacuum than in air!

Archimedes’ PrincipleArchimedes’ Principle

• What does a helium balloon do in an accelerating car? Why?What does a helium balloon do in an accelerating car? Why?

Archimedes’ PrincipleArchimedes’ Principle

• What does a helium balloon do in an accelerating car? Why?What does a helium balloon do in an accelerating car? Why?

Bernoulli’s PrincipleBernoulli’s Principle

Water speeds up in narrower pipes!Where Speed of fluid increases, pressure in fluid decreases

Bernoulli’s PrincipleBernoulli’s Principle

Bernoulli’s PrincipleBernoulli’s Principle

Plasma – the Fourth State of MatterPlasma – the Fourth State of Matter

• Solid Liquid Gas PlasmaSolid Liquid Gas Plasma

Increasing Temperature Increasing Temperature

Plasmas are generally greater than 10,000 degreesPlasmas are generally greater than 10,000 degrees

Plasma – the Fourth State of MatterPlasma – the Fourth State of Matter

• A plasma is an ionized gas that responds to electric and magnetic A plasma is an ionized gas that responds to electric and magnetic fields.fields.

• The visible universe is made of 99% plasma.The visible universe is made of 99% plasma.

• The sun is a giant ball of plasmaThe sun is a giant ball of plasma

• High temperature Plasma must be contained in magnetic bottles. If the High temperature Plasma must be contained in magnetic bottles. If the plasma were to come into contact with a physical container, it would plasma were to come into contact with a physical container, it would vaporize the container.vaporize the container.

• Lightning is a plasmaLightning is a plasma

• Fusion power research uses a plasma at ~ 10M Fusion power research uses a plasma at ~ 10M ooCC

Plasmas – Fluorescent LampsPlasmas – Fluorescent Lamps

• Fluorescent lamp – argon and mercury atoms ionize creating plasma Fluorescent lamp – argon and mercury atoms ionize creating plasma where current flows. Current activates mercury atoms to emit where current flows. Current activates mercury atoms to emit ultraviolet radiation causing phosphor coating on inner surface of tubes ultraviolet radiation causing phosphor coating on inner surface of tubes to glow visible light.to glow visible light.

• Other gasses glow colors: Neon – red, argon – blue, sodium – yellow, Other gasses glow colors: Neon – red, argon – blue, sodium – yellow, helium – pink.helium – pink.

Plasmas – Fluorescent LampsPlasmas – Fluorescent Lamps

• What keeps fluorescent lights from getting extremely hot??What keeps fluorescent lights from getting extremely hot??

• Each of the ions in the plasma does have a high temperature, but each Each of the ions in the plasma does have a high temperature, but each ion can only carry a small amount of energy. Since there are very few ion can only carry a small amount of energy. Since there are very few total ions and electrons in the tube, not much energy can be total ions and electrons in the tube, not much energy can be transferred.transferred.

Class ProblemClass Problem

Compared to the mass of a dozen eggs, Compared to the mass of a dozen eggs, the mass of air in an "empty the mass of air in an "empty refrigerator" isrefrigerator" is

1) negligible1) negligible2) about a tenth as much2) about a tenth as much3) about the same3) about the same4) more 4) more

Class ProblemClass Problem

• Compared to the mass of a dozen eggs, the mass of air in Compared to the mass of a dozen eggs, the mass of air in an "empty refrigerator" isan "empty refrigerator" is

a) negligiblea) negligibleb) about a tenth as muchb) about a tenth as muchc) about the samec) about the samed) more d) more

• One cubic meter of air at 0°C and normal One cubic meter of air at 0°C and normal atmospheric pressure has a mass of atmospheric pressure has a mass of about 1.3 kilograms. A medium-sized about 1.3 kilograms. A medium-sized refrigerator has a volume of about 0.6 refrigerator has a volume of about 0.6 cubic meter and contains about 0.8 cubic meter and contains about 0.8 kilograms of air—more than the 0.75 kilograms of air—more than the 0.75 kilograms of a dozen large eggs!kilograms of a dozen large eggs!

We don't notice the weight of air because We don't notice the weight of air because we are submerged in air. If someone we are submerged in air. If someone handed you a bag of water while you handed you a bag of water while you were submerged in water, you wouldn't were submerged in water, you wouldn't notice its weight either. notice its weight either.

Class ProblemClass Problem

• In the presence of air, the small iron In the presence of air, the small iron ball and large plastic ball balance ball and large plastic ball balance each other. When air is evacuated each other. When air is evacuated from the container, the larger ballfrom the container, the larger ball

1) rises1) rises

2) falls2) falls

3) remains in place 3) remains in place

Class ProblemClass Problem• In the presence of air, the small iron ball In the presence of air, the small iron ball

and large plastic ball balance each and large plastic ball balance each other. When air is evacuated from the other. When air is evacuated from the container, the larger ballcontainer, the larger ball

a) risesa) risesb) fallsb) fallsc) remains in place c) remains in place

• The answer is b:The answer is b:

Before evacuation, the forces acting on Before evacuation, the forces acting on each ball are the gravitational force, the each ball are the gravitational force, the force exerted by the balance beam and force exerted by the balance beam and the upward buoyant force exerted by the the upward buoyant force exerted by the surrounding air. Evacuating the surrounding air. Evacuating the container removes the buoyant force on container removes the buoyant force on each ball. Since buoyant force equals each ball. Since buoyant force equals the weight if air displaced, and the larger the weight if air displaced, and the larger ball displaces the greater weight of air, ball displaces the greater weight of air, the loss of buoyant force is greater for the loss of buoyant force is greater for the larger ball, which falls. the larger ball, which falls.

Class ProblemClass Problem

• Consider a Ping-Pong ball floating in a Consider a Ping-Pong ball floating in a glass of water that is enclosed in an air-glass of water that is enclosed in an air-tight chamber. When air pressure is tight chamber. When air pressure is increased in the chamber, does the ball increased in the chamber, does the ball floatfloat

1) lower, 2) higher, or 3) as before?

Class ProblemClass Problem

• Consider a Ping-Pong ball floating in Consider a Ping-Pong ball floating in a glass of water that is enclosed in an a glass of water that is enclosed in an air-tight chamber. When air pressure air-tight chamber. When air pressure is increased in the chamber, does the is increased in the chamber, does the ball float lower, higher, or as before? ball float lower, higher, or as before?

• The ball will float higher. The The ball will float higher. The buoyancy that accounts for its buoyancy that accounts for its floatation is due to the weight of the floatation is due to the weight of the displaced fluid—both air and water. displaced fluid—both air and water. Higher-pressure air is denser air, and Higher-pressure air is denser air, and the greater weight of displaced the greater weight of displaced denser air by the ball contributes to denser air by the ball contributes to greater buoyancy by the air. This lifts greater buoyancy by the air. This lifts the ball upward and the ball floats the ball upward and the ball floats higher in the water. higher in the water.

Class ProblemClass Problem

• If you release a ball inside a freely-If you release a ball inside a freely-falling elevator, it stays in front of falling elevator, it stays in front of you instead of "falling to the floor" you instead of "falling to the floor" because you, the ball, and the because you, the ball, and the elevator are all accelerating elevator are all accelerating downward at the same acceleration, downward at the same acceleration, gg. If you similarly release a helium-. If you similarly release a helium-filled balloon, the balloon willfilled balloon, the balloon will

1) also stay in front of you1) also stay in front of you2) press against the ceiling2) press against the ceiling3) press against the floor 3) press against the floor

Class ProblemClass Problem• If you release a ball inside a freely-falling elevator, it stays in front of you instead of "falling to the floor" because If you release a ball inside a freely-falling elevator, it stays in front of you instead of "falling to the floor" because

you, the ball, and the elevator are all accelerating downward at the same acceleration, you, the ball, and the elevator are all accelerating downward at the same acceleration, gg. If you similarly release a . If you similarly release a helium-filled balloon, the balloon will:helium-filled balloon, the balloon will: a) also stay in front of you

b) press against the ceilingc) press against the floor

The answer is The answer is aa::

Like the falling ball, the balloon will also stay in front of you because it loses its buoyancy. The buoyancy of a Like the falling ball, the balloon will also stay in front of you because it loses its buoyancy. The buoyancy of a balloon is the result of a difference in air pressure against it—usually a greater pressure acting up against the balloon is the result of a difference in air pressure against it—usually a greater pressure acting up against the bottom than down against the top. But in the freely-falling environment there is no difference in air pressure. Air in bottom than down against the top. But in the freely-falling environment there is no difference in air pressure. Air in the elevator, like everything else inside, is in a state of free fall. Air in the top part does not press against air in the the elevator, like everything else inside, is in a state of free fall. Air in the top part does not press against air in the bottom part to give a greater pressure there. No pressure difference means no buoyancy, so the balloon freely falls bottom part to give a greater pressure there. No pressure difference means no buoyancy, so the balloon freely falls like everything else inside the elevator. like everything else inside the elevator.

Class ProblemClass ProblemA block of wood and a block of iron on weighing scales each weigh 1 ton. Strictly A block of wood and a block of iron on weighing scales each weigh 1 ton. Strictly

speaking, which has the greater mass? speaking, which has the greater mass?

1) wood2) iron3) same

Class ProblemClass Problem

A block of wood and a block of iron on weighing scales each weigh 1 ton. Strictly speaking, which A block of wood and a block of iron on weighing scales each weigh 1 ton. Strictly speaking, which has the greater mass? has the greater mass?

• Answer:Answer:• The wood has the greater mass. Why? Because the scale reading is weight The wood has the greater mass. Why? Because the scale reading is weight minusminus

the buoyant force of the surrounding air. The wood has a greater volume, displaces the buoyant force of the surrounding air. The wood has a greater volume, displaces more air, and therefore has a greater buoyant force. To yield the same scale more air, and therefore has a greater buoyant force. To yield the same scale reading it must therefore have a greater mass than the iron. reading it must therefore have a greater mass than the iron.

Class ProblemClass Problem

• A birthday candle burns in a deep A birthday candle burns in a deep drinking glass. When the glass is drinking glass. When the glass is whirled around in a circular path, whirled around in a circular path, say held at arm's length while one is say held at arm's length while one is spinning like an ice skater, which spinning like an ice skater, which way does the candle flame point? way does the candle flame point?

1. straight up

2. inwards towards the center of motion

3. outward away from the center of motion

Class ProblemClass Problem

• A birthday candle burns in a deep drinking A birthday candle burns in a deep drinking glass. When the glass is whirled around in a glass. When the glass is whirled around in a circular path, say held at arm's length while one circular path, say held at arm's length while one is spinning like an ice skater, which way does is spinning like an ice skater, which way does

the candle flame point?the candle flame point?

• The candle flame points inward, The candle flame points inward, toward the center of the circular toward the center of the circular motion. This is because the air motion. This is because the air in the glass is more dense than in the glass is more dense than the flame and "sloshes" to the the flame and "sloshes" to the farther part of the glass. The farther part of the glass. The greater air pressure at the greater air pressure at the farther part of the inner glass farther part of the inner glass then buoys the flame to the then buoys the flame to the region of lesser pressure—region of lesser pressure—inward. inward.

Class ProblemClass Problem

• A candle will stay lit inside the A candle will stay lit inside the space shuttle when it is on the space shuttle when it is on the launch pad, but when not when it is launch pad, but when not when it is in orbit. Why? in orbit. Why?

Class ProblemClass Problem

• When a candle ordinarily burns, the When a candle ordinarily burns, the warmed carbon dioxide produced in warmed carbon dioxide produced in the flame rises by convection, and the flame rises by convection, and oxygen comes in from below to oxygen comes in from below to keep the process going. But when in keep the process going. But when in orbit, there is no effect of gravity orbit, there is no effect of gravity inside the cabin and convection inside the cabin and convection cannot occur. The warmed exhaust cannot occur. The warmed exhaust gasses do not "rise," and instead gasses do not "rise," and instead suffocate the flame. suffocate the flame.

Class ProblemClass Problem

1. Atmospheric pressure is caused by the A) density of the atmosphere. B) weight of the atmosphere. C) temperature of the atmosphere. D) effect of the sun's energy on the atmosphere

2. A balloon is buoyed up with a force equal to the A) weight of air it displaces. B) density of surrounding air. C) atmospheric pressure. D) weight of the balloon and contents. E) all of these

3. As a helium-filled balloon rises in the air, it becomes A) bigger. B) more dense. C) heavier. D) all of these E) none of these

Class ProblemClass Problem

4. In drinking soda or water through a straw, we make use of A) capillary action. B) surface tension. C) atmospheric pressure. D) Bernoulli's principle. E) none of these

5. Airplane flight best illustrates

A) Archimedes' principle. B) Pascal's principle. C) Bernoulli's principle. D) Boyle's law.

6. A suction cup sticks to a wall. It is A) pulled to the wall by the vacuum. B) pushed to the wall by the atmosphere. C) both of these D) neither of these

Class ProblemClass Problem

7. As a balloon rises higher and higher into the atmosphere, its A) volume decreases. B) density increases. C) weight increases. D) mass decreases. E) none of these

8. Compared to the buoyant force of the atmosphere on a 1-liter helium-filled balloon, the buoyant force of the atmosphere on a nearby 1-liter solid iron block is

A) considerably less. B) considerably more. C) the same.

9. When gas in a container is squeezed to half its volume, its density A) halves. B) doubles. C) quadruples. D) remains the same.

Class ProblemClass Problem

10. In a vacuum, an object has no A) buoyant force. B) mass. C) weight. D) temperature. E) all of these

11. Suspend a pair of Ping-Pong balls from two strings so there is a small space between them. If you blow air between the balls, they will swing

A) toward each other. B) apart from each other. C) away from the air stream, but not necessarily toward or apart from each other.

12. The main difference between gases and plasmas has to do with A) the kinds of elements involved. B) interatomic spacing. C) electrical conduction. D) fluid pressure. E) the proportion of matter to antimatter in the universe.