Air Pressure 7.2Density and Pressure of Air

The air is made up of molecules.

• Properties of Air

Eureka DensityDensity Density 2

•Air has mass.

•Since air has mass, it has other properties, including density and pressure.

Density

• Density • Amount of mass in a given volume

Density = 5 circles per cube

Density

• Density • Amount of mass in a given volume

Density = 11 circles per cube

Temperature Affects Density

Density = 6 circles per cube2 circles per cube

Temperature Affects Density

Density = 3 circles per cube10 circles per cube

Which rises and which sinks?

Density =5 circles per balloon

Density =2 circles per balloon

• Density

Eureka DensityDensity Density 2

If the molecules are real close the density is higher.

If the molecules are spread further apart the density is lower.

Density

Which is Denser?

Which cookie has more chocolate chips?

Cookie A is denser . It has more chocolate chips in the same size cookie than cookie B.

If I wanted to make a cookie less dense I would use the same amount of chocolate chips just make the cookie bigger.

A B

Which is state of water is least dense? Most dense?

liquidSolid Gas

Molecules move very slowly! They are close together.

Molecules move faster and are more spread apart.

Molecules move very fast! They are very spread apart.

Most Dense Least Dense

Air and Density Clip

Density of warm and cold air.

Warm Air

Less Dense

Molecules are further apart.

Air is lighter.

Cold Air

more Dense

Molecules are closer together.

Air is heavier.

Warm Air

Less Dense

Molecules are further apart.

Air is lighter.

Cold Air

more Dense

Molecules are closer together.

Air is heavier.

Density?

Molecular spacing?

Weight?

Temperature

Density?

Molecular spacing?

Weight?

Temperature

Pair/ Share

•Convection currents happen because hot air rises. It rises because it is less dense and lighter.

•Cold air sinks because it is more dense and heavier.

Why do convection current occur?

Pair/Share

•Explain how a convection current works.

•Use words like: density, temperature, molecules, weight

Air Pressure and Altitude

Most Dense

Less Dense

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Gravity pulls the air Gravity pulls the air molecules toward molecules toward the earth, giving the earth, giving them weight. The them weight. The weight of the air weight of the air molecules all around molecules all around us is called the air us is called the air pressure.pressure.

•The pressure acting on the surface of the earth is called atmospheric pressure.

•It is caused by the weight of a column of air pressing down on the surface of Earth.

•Atmospheric pressure is measured by a barometer.

Atmospheric Pressure

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Air pressure Air pressure is equal in all is equal in all

directions.directions.

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to to measure measure air air pressure.pressure.

A A BarometerBarometer

is is usedused

An aneroid barometer uses a cell which has had most of An aneroid barometer uses a cell which has had most of the air removed. the air removed.

As the air pressure around the cell increases, it presses As the air pressure around the cell increases, it presses on the cell, which causes the needle to move. on the cell, which causes the needle to move. Barometer Clip Barometer Clip

MILLIBARS

•The lower we travel down into the atmosphere the more weight there is above, and so the tighter the air is squished or compacted.

•Low altitude = high air pressure

•High altitude = low air pressure

ALTITUDE AND AIR PRESSURE

So why is it harder to breath at higher altitudes?

Altitude vs Air pressure Clip

Since pressure changes with altitude…Since pressure changes with altitude…

……how does changing altitude affect how does changing altitude affect a barometer?a barometer?

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As As elevation elevation goes upgoes up

Barometric Barometric pressure pressure

goes down.goes down.

This is an inverse This is an inverse relationship.relationship.

Can you feel air pressure?

When you take off or land in an aircraft, your ears may hurt or feel uncomfortable. This is because your eardrums can feel changes in air pressure as the aircraft moves quickly up and down.

Astronauts wear space suits so the can pressurize themselves in the space suit. With out a space suit an astronaut would explode. More inside body pressure than outside pressure.

Submarines have to be made very strong to withstand the enormous pressure exerted by the water. If they go too low in altitude they will implode.

9 min video on Air pressure

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Most aneroid Most aneroid barometers have a barometers have a needle which can needle which can be set to be set to remember the remember the previous reading.previous reading.

Why would this Why would this be important?be important?

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Changing PressureChanging Pressure

A A rising barometerrising barometer = increasing air pressure. = increasing air pressure.

This usually means:This usually means:

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Changing PressureChanging Pressure

A A falling barometerfalling barometer = decreasing air pressure. = decreasing air pressure.

This usually means:This usually means:

Where’d the hula dancer

go?

Why do baseball players like to play in Denver, Colorado?

• Heat wind and pressure clip