Review  for  NC  Final  Exam,  Unit  1  

7th  Grade  Science  

Problem/QuesCon  ObservaCon/Research  Formulate  a  Hypothesis  

Experiment  Collect  and  Analyze  Results  

Conclusion  Communicate  the  Results  

Independent  Variables  

• What is tested by the scientist • What is changed by the

scientist • Also known as manipulated

variables.

Dependent  Variable    

•  What is observed •  What is measured •  The effect caused by the

independent variable. •  The data •  Also called responding variables

Controlled  Variables    (Controls/Control  Group)  

• Things that could change but don’t

•  Kept constant (the same) by scientists

• These allow for a fair test.

Mixture of Gases in Air

All  Other  Gases  Argon  =  0.93%  

Carbon  Dioxide  =  0.04%  

CARBON DIOXIDE •  What we exhale & used by plants

for photosynthesis •  A greenhouse gas – carbon dioxide

helps keep our planet warm •  Increases in CO2 have been making

the planet warmer: global warming! •  #1 way Carbon Dioxide is increasing

is burning of fossil fuels.

DENSITY •  DENSITY describes how closely packed

the particles of an object are.

HIGH density LOW density

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.

As elevation goes up

Barometric pressure

goes down.

This is an inverse relationship.

Air Pressure at Different Altitudes Is air pressure greater at sea level or on

top of a mountain?

Higher Air Pressure

Lower Air Pressure

Sea Level (Low altitude)

Mountains (High altitude)

The Atmosphere §  The layer of gases (AIR) that surrounds

the earth.

§  It stretches more than 400 km above us.

Layers of the Atmosphere Foldable

Today, we’re going to learn about the different parts of our atmosphere. There are 4 main LAYERS of the atmosphere. Label the outside of your foldable as shown here. The surface of the earth is down here

Troposphere  

Stratosphere  

Mesosphere  

Thermosphere  

Layers  of  the  Atmosphere   400  km  

80  km  

50  km  

12  km  

0  km  

1st  2  Layers  of  the  Atmosphere  (starCng  closest  to  the  Earth)    

TROPOSPHERE  •  All of Earth’s

weather happens here.

•  Air here contains water & dust.

•  Most of the atmosphere’s air is here (this layer is very dense).

STRATOSPHERE  •  There is no water

or dust in this layer.

•  Contains the OZONE LAYER (which absorbs UV radiation from the sun)

•  Air is less dense than troposphere.

2nd  2  Layers  of  the  Atmosphere  

MESOSPHERE  •  Temperature

plunges to -90°C (the coldest in the atmosphere)

•  Meteors burn up here while entering the atmosphere.

•  Air is thinner here.

THERMOSPHERE  •  Air is extremely

thin. Atmospheric gases fade into outer space.

•  Satellites and shuttles orbit here.

•  Temperature can spike to 1,800°C.

What is heat, anyway? •  Temperature is a measure of the

average amount of energy of motion for each particle of a substance

Cold Water - Slow-

Moving Molecules

Hot Water- Fast-

Moving Molecules

Nearly all the energy that heats our atmosphere comes from the sun.

•  Energy from the sun travels in the form of electromagnetic waves.

•  Not all sunlight reaches the ground. Some sunlight is

absorbed or reflected before it reaches the surface.

How does heat move?

•  HEAT is the transfer of thermal energy from a hotter object to a cooler one.

•  Thermal energy is moving from the air, which is warmer, to the snowman, which is cooler.

How does heat move?

•  Heat can be transferred in three ways: radiation (waves), conduction (touching solid surfaces), and convection (rising/falling in fluids).

HEAT TRANSFER

Cold  air  moves  pre^y  slowly,  and  stays  pre^y  Cghtly  packed  together:  

Hot  air,  on  the  other  hand,  goes  really  fast  and  expands  

to  fill  more  space.  

Physical properties of the atmosphere: Density

•  Warm, low density air rises

•  Cool, high density air sinks

•  Creates circular- moving loop of air (convection cell) Figure 6-5

Where does the energy go?

•  The color and material of the surface will determine how much of the energy is absorbed and how much is reflected. Dark colors ABSORB more sunlight than lighter colors.

Water

Rocks

Grass

Sand

So,  hot  air  is  LESS  DENSE  than  cold  air.  So,  since  hot  air  is  less  dense  than  the  surrounding  air,  it  rises,  leaving  a  low-­‐density,  low-­‐pressure  area  behind.    

Nearby  cold  air  can  then  rush  in  to  fill  low-­‐pressure  area  leb  by  the  rising  hot  air.    

This  rushing  in  of  cold  air  is  what  we  call…  

WIND!!    

 

Coriolis  Effect  •  The  reason  that  winds  blow  in  a  curved  manner  instead  of  a  straight  line  because  of  the  way  the  Earth  rotates.    

•  So the Coriolis Effect causes wind flowing from high pressure to low pressure to curve as the wind moves.

•  In the Northern Hemisphere, The Coriolis Effect causes things to curve to the Right. In the Southern Hemisphere, the Coriolis Effect causes things to curve to the Left.

 

How much water can air hold? •  HUMIDITY  is  the  measure  of  how  much  water  vapor  is  in  the  air.    

•  TEMPERATURE  affects  how                          much  water  vapor  the  air  can  hold…  

holds  MORE  water  vapor.   holds  LESS  water  vapor.  

That’s why air feels more “HUMID” on hot days!

What is the “Dew Point”? •  As air cools, the amount of water

vapor it can hold decreases. •  At a certain temperature, the water

vapor in the air will CONDENSE back into water droplets or ice.

•  This temperature is the “DEW POINT”.

What are CLOUDS? •  They are made of tiny water droplets or

ice crystals. •  They form when water condenses onto

small particles in the air (like dust).

How do clouds form?

1)   Warm, moist

air rises and cools.

2) Water Air cools to dew point

causing condensation.

.

3) Water vapor Condenses,

forming a cloud.

Flat clouds = “Stratus”

Fluffy clouds = “Cumulus”

Wispy clouds = “Cirrus”

Clouds are classified according to SHAPE

Clouds are also classified by ALTITUDE

HIGH LEVEL (cirro-)

MID LEVEL (alto-)

LOW LEVEL (stratus)

What  is  an  AIR  MASS?  

•  An  air  mass  is  a  huge  body  of  air  that  influences  weather.  

•  ScienKsts  classify  air  masses  based  on:      TEMPERATURE            and              HUMIDITY  

North  American  Air  Masses:  How  do  these  air  masses  move?  (like  most  of  our  winds  and  

weather  –  from  West  to  East)  MARITIME

POLAR CONTINENTAL

POLAR MARITIME

POLAR

MARITIME TROPICAL

MARITIME TROPICAL

CONTINENTAL TROPICAL

Prevailing Westerlies

Jet Stream Prevailing Westerlies

What  happens  when  air  masses  meet?  

•  Air  masses  don’t  mix  easily.  •  The  line  between  air  masses  is  called  a  front.  

Compare/Contrast Chart - Types of Fronts

Front How it Forms Type of Weather

Cold Front

A fast-moving cold air mass overtakes a warm air mass.

Clouds form. If warm air is humid, rain/snow may fall. Possible thunderstorms.

Warm Front

A warm air mass overtakes a slow-moving cold air mass.

Scattered clouds. Light rain or snow. May last several days.

Stationary Front Cold and warm air meet, but neither can move the other. Creates “standoff”

Rain, snow, clouds, or fog that may last for days.

Occluded Front A warm air mass is caught between 2 cooler air masses. Warm air mass is pushed up.

Temperature gets cooler. Clouds and rain may form.

High  and  Low  Pressure  Systems  •  High  Pressure  System  usually  brings  clear,  calm,  and  dry  weather  

•  Low  Pressure  System  usually  brings  clouds,  rain,  &  wind  

Weather  Tools    

An  anemometer  measures  wind  speed.  

A  hygrometer  is  used  to  measure  humidity.    

Weather  Tools  -­‐  Barometer  

•   A  barometer  is  used  to  measure  air  pressure.  

Thunderstorms  

u A thunderstorm is a storm that generates lightning and thunder. Thunderstorms frequently produce gusty winds, heavy rain, and hail.

u Thunderstorms are usually formed from Cumulo-Nimbus Clouds

Tornadoes

20.3    Severe  Storms          

u Tornadoes are violent windstorms that take the form of a rotation column of air called a vortex. The vortex extends downward from a cumulonimbus cloud.

Most tornadoes form in association with severe thunderstorms.

•  Tornadoes are measured on the Fujita Scale (1-5)

•

Hurricanes  

u Whirling tropical cyclones that produce winds of at least 119 kilometers per hour are known in the United States as hurricanes.

Hurricanes develop most often in the late summer when water temperatures are warm enough to provide the necessary heat and moisture to the air.

The eye is a zone of scattered clouds and calm averaging about 20 kilometers in diameter at the center of a hurricane.

Hurricanes are measured on the Saffir-Simpson Hurricane Scale (1-5).

• Most hurricanes form off the western coast of Africa and travel West, toward North America

Air Pollution: • Any visible or invisible particle or gas found in the air that is not part of the original, normal composition. It is measured by the AQI: (Air Quality Index).

It  can  be  from  natural  or  manmade  sources    

Too much of a good thing •  Carbon Dioxide is a blessing

–  It is a crucial source of all our food – without photosynthesis could not occur

– Without it we would freeze to death

•  Carbon Dioxide is a potential menace –  It is such as powerful heat

absorber that small increases in its level along with other greenhouse gases can have dramatic effects on our climate

• Greenhouse effect -It generally comes from the build up of carbon dioxide gas in the atmosphere. Carbon dioxide is produced when fuels are burned. -In this type of pollution sun rays go into the atmosphere and they are trapped by greenhouse-gasses. So the temperature on the earth raise.

•  Hole in the ozone layer        -­‐It’is  another  result  of  polluCon.  Chemicals  released  by  our  acCviCes  affect  the  stratosphere.    

       -­‐Releases  of  CFC  from  heaCng,  aerosol  cans,  refrigerator  equipment  removes  some  of  the  ozone,  causing  "holes”.  

• Acid rains  -It’s caused when a pollutant combines with droplets of water in the air. -The effects of acid rain on the environment can be very serious.