Air Pressure 7 2 Density and Pressure of

Air Pressure 7. 2 Density and Pressure of Air

The air is made up of molecules.

• Properties • Air has mass. of Air Eureka Density 2 • 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 2 circles per Density = 6 cube

Temperature Affects Density 10 circlesper Density = 3 cube per cube

Which rises and which sinks? Density = 5 circles per balloon Density = 2 circles pe balloon

• Density Eureka 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? A B If I wanted to make a cookie less dense Cookieuse A isthe denser It has more I would same. amount of chocolate chips in the same chocolate chips just make the size cookie than cookie B. bigger.

Which is state of water is least dense? Most dense? Solid Molecules move very slowly! They are close together. Most Dense liquid Gas Molecules move very fast! They are very spread apart. Least Dense Molecules move faster and are more spread apart. 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.

Pair/ Share Temperature Cold Air Temperature Warm Air more. Density? Dense Less. Density? Dense Molecules are Molecular spacing? closer together. Air is. Weight? heavier. Molecules are Molecular spacing? further apart. Air is. Weight? lighter.

Why do convection current occur? • 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.

Pair/Share • Explain how a convection current works. • Use words like: density, temperature, molecules, weight

Air Pressure and Altitude Less Dense Most Dense

Gravity pulls the air molecules toward the earth, giving them weight. The weight of the air molecules all around us is called the air pressure. 18

Atmospheric 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.

Air pressure is equal in all directions. 20

A Barometer is used to measure air pressure. 21

MILLIBARS An aneroid barometer uses a cell which has had most of the air removed. As the air pressure around the cell increases, it presses on the cell, which causes the needle to move. Barometer Clip

ALTITUDE AND AIR PRESSURE • 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 So why is it harder to air pressure breath at higher • High altitude = low air altitudes? pressure Altitude vs Air pressure Clip

Since pressure changes with altitude… …how does changing altitude affect a barometer?

As elevation goes up Barometric pressure goes down. This is an inverse relationship. 25

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

Most aneroid barometers have a needle which can be set to remember the previous reading. Why would this be important? 29

Changing Pressure A rising barometer = increasing air pressure. This usually means: 30

Changing Pressure A falling barometer = decreasing air pressure. This usually means: Where’d the hula dancer go? 31

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

• Heat wind and pressure clip