Chapter 14: Gases Flashcards
Gas
No definite shape or volume
The atmosphere
1) Ocean of air/gases
2) Exerts pressure
3) Competing factors
4) Without the sun, molecules fall to Earth (Earth’s gravity wins)
5) WIthout the Earth’s gravity, molecules fly into space (“Sun wins”)
Competing factors
1) Kinetic energy of molecules (Energized by sunlight)
2) Gravity (Pulled down by Earth)
Lived at the bottom of an ocean of air (gases)
1) p(liquid) = nearly constant
2) p(atmosphere) = varies a lot
Air becomes less dense with
Increasing altitudes (30 km thick atmosphere)
Air is more compressed/dense at sea level than at
Higher altitude
Liquid (less pressure)
Bottom layer experiences more pressure than the upper layer
Liquid (more pressure)
Each layer holds the weight of the previous layers
Atmosphere is divided into 5 layers
1) Pressure = Less = Exosphere
2) Pressure = Less = Thermosphere
3) Pressure = Less = Mesosphere
4) Pressure = Less = Stratosphere
5) Pressure = High = Troposphere
Air pressure, like water, acts equally in
All directions at a specified height
Just as water pressure is caused by
The weight of water
Atmospheric pressure is caused by
The weight of air
Air is being pulled down by
The gravitational force
Atmosphere pressure varies from
One locality to another
Atmosphere pressure surrounded by
Air in all directions
Pressure decreases with
Increasing altitude
The barometer is a device to
Measure atmospheric pressure
Pressure consists of a mercury tube
Upside down in a dish filled mercury
Pressure the height of the mercury column tells us
The atmospheric pressure
Mercury column exerts pressure on
The mercury in the dish
Atmosphere exerts pressure on
The mercury in the dish
These two pressures must be equal so that
The atmospheric pressure supports the mercury column
The pressure and volume of a gas enclosed in a space are
Inversely proportional
Piston
A disk or short cylinder that moves up or down against a liquid or gas
If you increase pressure, the volume will
Decrease by the same factor
Boyle’s Law
The pressure and volume of a gas enclosed in a space are inversely proportional
The product of pressure and volume of a given mass of gas will always
Remain the same
Buoyancy of Air
Archimedes’s principle applies to air as well as liquids
An object surrounded by
Air is buoyed up by a force equal to the weight of the air displaced
Rule for “Lighter than air” objects
1) When the weight of air displaced by an object is greater than the weight of the object, it rises
2) When the weight of air displaced by an object equals the weight of the object, it hovers in air
3) When the weight of air displaced by an object is less than the weight of the object, it is supported by air
1) When the weight of air displaced by an object is greater than the weight of the object, it rises
W(ob) < W(disp)
2) When the weight of air displaced by an object equals the weight of the object, it hovers in air
W(ob) = W(disp)
3) When the weight of air displaced by an object is less than the weight of the object, it is supported by air
W(ob) > W(disp)
Gas filled balloons
Buoyancy with hydrogen, the lightest gas (flammable seldom used) and next best buoyancy with helium
As balloons rise, atmosphere becomes
Less dense since pressure decreases, volume increases then the balloon expands
Gas-filled balloon will continue to rise until the weight of displaced air equals
The total weight of the balloon
The buoyant force on the balloon equals
Its weight which says the same thing
Bernoulli’s Principle
Where the speed of a fluid increases, internal pressure in the fluid decreases (and vice versa)
Bernoulli’s Principle applies to a smooth, steady flow
1) Mainly applied to incompressible fluids
2) Fluid with constant density
Bernoulli’s Principle farther apart
1) Flow speed is less
2) Pressure within the fluid is greater
Bernoulli’s Principle closer apart
1) Flow speed is greater
2) Pressure within the fluid is less
Applications of Bernoulli’s Principle
1) Blow on the top surface of a paper and the paper rises
2) Reasons: Pressure of the moving air is less than the atmospheric pressure beneath it
Wind blowing above and below an airplane wing produces lift
Reasons: Air velocity is greater over the top of the wing than the bottom. Pressure is greater at the bottom and produces lift
Plasma
An electrified gas
Atom in a plasma are
Ionized and stripped of one or more electrons, with a corresponding number of tree electrons
Sun and other stars contain
Plasma
Aurora borealis and the aurora australis are
Glowing plasma in the upper atmosphere
Fluorescent lamps and neon signs - When a lamp is turned on, a high voltage between electrodes of the tube causes
Electron to flow
Electrons ionize some atoms
Forming plasma
Plasma provide a conducting path that
Keeps the current flowing
Radiations causes the phosphor coating on the tube’s inner surface to glow with
The visible light
