air pressure and hot air balloons!. hot air balloons!!! have you ever seen a hot air balloon? what...

Air Pressure and Hot Air Air Pressure and Hot Air Balloons!Balloons!

Hot Air Balloons!!!Hot Air Balloons!!!

• Have you ever seen a hot air balloon?• What makes it fly through the air?

Air pressure is a bigpart of how hot airballoons work.

An Ocean of Air?An Ocean of Air?

• The air that surrounds us is composed of many different elements such as oxygen, nitrogen, and hydrogen.

• These elements, in their gaseous state, fly around freely.

• Every time they bump into each other, or another object, they push using a tiny bit of energy.

The Nature of GasesThe Nature of Gases

Gases expand to fill their containers Gases are fluid – they flow Gases have low density

1/1000 the density of the equivalent liquid or solid

Gases are compressible Gases effuse and diffuse

Kinetic Molecular TheoryKinetic Molecular TheoryParticles of matter are

ALWAYS in motionVolume of individual particles

is zero.Collisions of particles with

container walls cause the pressure exerted by gas.

Particles exert no forces on each other.

Average kinetic energy is proportional to Kelvin temperature of a gas.

Air Density & TemperatureAir Density & Temperature

When a cold tire is inflated to a certain pressure and then When a cold tire is inflated to a certain pressure and then is warmed up due to friction with the road, the pressure is warmed up due to friction with the road, the pressure

increases. This happens because…increases. This happens because…

1. Air molecules hit the walls of the tire less frequently

2. Rubber in the tire reacts with oxygen in the atmosphere

3. Air molecules speed up and collide with the tire walls more often

4. Air molecules diffuse rapidly through the walls of the tire

Kinetic Energy of Gas ParticlesKinetic Energy of Gas Particles

At the same conditions of temperature, all gases have the same average kinetic energy.

m = mass

v = velocity2

21 mvKE

At the same temperature, small small moleculesmolecules move FASTERFASTER than large molecules

Air PressureAir Pressure

• Because there are millions of particles in the atmosphere, the energy released upon interactions adds up quickly.

• This is called air pressure.• The air pressure at sea

level is about 1 kilogramper square centimeter.

Don’t Get Pushed Around!Don’t Get Pushed Around!

• Our bodies do not feel the air pressure normally because it disperses evenly around us.

• Hold out your hand, palm up.• The air pressure exerted on the top of your

hand is equal to the pressure of the air pushing up on the bottom of your hand.

• The forces cancel out, and you don’t feel the effects of air pressure.

GravityGravity

• In a scenario where only air pressure exists, everything would be evenly balanced out.

• However, we live on a planet in which gravity plays a huge part.

Gravity vs. Air PressureGravity vs. Air Pressure

• Gravity pulls downward on everything, and its effects extend to even our atmosphere.

• But the air pressurecreates an upwardforce to counteractgravity.

• There is more air pressure at sea level because the air at that level has to support all the air above it.

Altitude and Air PressureAltitude and Air Pressure

• As you move away from sea level, the air pressure lessens.

• The air pressure at the top of Mount Everest is incredibly low because there is much less air above for it to support.

• Climbers often breathe pressurized air when at high altitudes because their lungs cannot force such low pressure air into their bodies.

Hot Air BalloonsHot Air Balloons

• This difference of air pressure causes an upward buoyant force all around us.

• This means that there is less air pressure above an object, than below it.

• This basic fact helps hot air balloons fly through the air.

Why HOT air balloons?Why HOT air balloons?

• Hot air is pumped into the balloon because as air is heated, the molecules in the air move faster.

• In the balloons, thismakes the air insidethe balloon movemuch faster than thecool air of our atmosphere.

Up, Up, and Away!!Up, Up, and Away!!

• The molecules that are moving faster hit the walls of the balloons more often, and at a greater force.

• This means that it takes less hot air molecules to equal the same air pressure of cooler air molecules.

• The hotter, less dense air inside the balloon help it rise against the cooler, denser atmospheric air.

How Air Pressure Affects the How Air Pressure Affects the WeatherWeather

• Atmospheric air pressure is never constant, but a column of air may have a relatively higher or lower pressure than nearby columns

• Vertical and horizontal air pressure gradients affect wind and precipitation.

• All weather is the effect of Earth correcting a temporary imbalance in the pressure or temperature gradient

To Learn More about Pressure To Learn More about Pressure Systems and WeatherSystems and Weather

• USA Today Weather Center:

http://www.usatoday.com/weather/wstorm0.htm

• Accuweather FAQ:

http://www.accuweather.com/iwxpage/paws/weathermapfaq.htm