Aim: How does measuring air pressure tell us about the Weather? Do Now: Answer the following questions in your notebook. 1. What happens to the air molecules when heat is added? 2. How does adding heat to the air change the density? 3. How does adding heat to the air change the air pressure? 4. What would happen to the air molecules if heat were to be removed? 5. What substance can be added to air to make it less dense?

I. Air Pressure - the pressure exerted by the weight of air (molecules) warm air = less dense therefore, less pressure cold air = more dense therefore, more pressure water vapor makes air less dense. Warm Air Cold Air How does the pressure exerted by cold and warm air differ? What else is different about them (besides their temperatures)

II. Temperature Changes Air Pressure A.Cold air - Gases compress making cold air more dense and able to sink. B. Warm air - Gases expand making warm air less dense and able to rise RISES SINKS Why does cold are sink while warm air rises?

-As pressure increases the liquid rises in the barometer. -As pressure decreases the liquid lowers in the barometer. III. Measuring Air Pressure What instrument measures air pressure? What can be added to the air to make the air pressure decrease?

A decreasing barometer (low pressure) means the weather will be cloudy and wet. An increasing barometer (high pressure) means the weather will be dry and sunny. More water vapor -> air is less dense -> air rises-> creates less pressure (low pressure) Less water vapor -> air is more dense -> air sinks-> creates more pressure (high pressure) List some of the difference between these two pictures (think about the information we have discussed so far) WET DRY

- Differences in air pressure creates wind. IV. Winds -Air moves from high pressure areas to low pressure areas (H L). What can we label the purple arrow in this picture? WIND

V. Pressure gradient: - Drawn using isobars. (just like contour lines!) Closely spaced isobars indicate high winds (steep gradient) Widely spaced isobars indicate light winds (gentle gradient)

On which side of the country would the strongest winds exist? What do you look for to answer this question?

Barometric Pressure Reading for April 6 th 2016 (Wednesday) Using the chart above, describe; 1) how the chart shows the weather was nice in the morning? 2) how the chart shows the weather was bad during the evening? 3) What changed in the air? High pressure = happy weather (rising barometer) Low pressure = lousy weather (falling barometer) 1) Pressure was high (rising) from 6am-10am 2) Pressure was low (falling) from 5pm to 11 pm. 3) More water vapor was entering the air, making the pressure decrease and causing lousy weather. Closure 1:

Closure: From the back table, take the worksheet on pressure and complete this working with your partner.