Scientist Guide Let s Talk About the Weather Introduction Agriculture is highly dependent on the weather. Ever since the first seed was sown, farmers have been watching the sky and hoping for good weather. Snows in the winter to keep the soil moist; rains in the spring to germinate seeds and provide vigorous growth; sun and frequent showers in the summer to provide energy for seed and robust stalks; dry fall days to allow for harvest and freedom from damaging winds and hail farmers are constantly monitoring the weather. Many of the things we depend on to survive the food we eat, the clothes we wear and the shelters we live in are products of agriculture, and their production can be affected by the weather. Therefore, it is important that we study, monitor and forecast the weather. Weather refers to the state of the atmosphere at a specific time and place. It describes conditions such as temperature, atmospheric pressure and dew point. Sun Clouds Temperature is a measure of the average amount of motion of molecules. When the temperature is high, molecules in the air move rapidly. When the temperature is low, molecules in the air move slowly. Thermometers are used to measure air temperature in degrees Fahrenheit ( F), Celsius ( C) or both. Sun s Heat Sun s Heat Cooling, Rising, Condensing Air Parcel (Blue dots represent moisture) Rising Warm Air Parcel Temperature plays an important role in our everyday lives. It helps us determine what to wear and what outdoor activities we can participate in. In agriculture, temperatures affect planting dates and the growth of plants, as well as insects and crop diseases. It also affects soil temperature and moisture content. Freezing temperatures in the fall generally mark the end of the growing season. Ground Figure 1. Warm Air Above The Ground Warm Ground Ground Atmospheric pressure determines the types of weather that are likely to occur. The types of weather affect the kind of field work that can be done and influence the effectiveness of herbicide and pesticide treatments.
Scientist Guide Air pressure and temperature play an important role in cloud formation. A cloud is a visible mass of condensed water vapor suspended in the atmosphere. Clouds are very important because they can produce rain that waters plants and crops. Clouds also shade the Earth, affecting the temperature. As the sun warms the ground, water evaporates, changing from a liquid to a gas known as water vapor. Water vapor is suspended in the air above the ground; the amount can be measured and is known as humidity. As the sun warms the air above the ground, the air expands and becomes less dense; expanding air has low atmospheric pressure and rises. As the warm air continues to rise, it starts to cool. This causes the water vapor to condense on microscopic dust particles (called condensation nuclei) and change from a gaseous state back into a visible, liquid state known as a cloud (Figure 1). Stormy and cloudy weather is associated with low pressure. Cooler air is denser and sinks because air molecules pack more closely together, leaving less room to move. Cool weather has high atmospheric pressure. Fair weather is usually associated with high pressure. Knowing the air pressure can help predict weather patterns. People, such as meteorologists, can measure air pressure in the atmosphere with an instrument called a barometer. The units of measurement for barometers are commonly in millibars (mb) or inches in mercury. The formation of liquid water from water vapor is called condensation. When there is enough water vapor in the air for condensation to occur, the air is saturated. The dew point is the temperature to which the air must be cooled to become saturated. Below the dew point, water will condense out of the air onto surfaces. In early morning, grass surfaces will be coated with water if nighttime temperature has dropped below the dew point. When the humidity is high, the dew point temperature is only a few degrees below, or equal to, air temperature.
Scientist Guide Activity Overview In this activity, you will conduct hands-on activities to improve your understanding of weather and some of the factors that influence it. Materials Cloud in a Bottle: 1-liter plastic bottle with cap Foot pump with rubber stop per attached Water Rubbing alcohol Make Your Own Thermometer: Glass test tube Rubbing alcohol, 91% Small cup Two 8 oz. disposable water bottles Red food coloring Parafilm Disposable pipette Hot water Ice water Making Dew: Small metal can Immersion thermometer Water Ice Rock salt Safety Precautions Do not eat or drink in the laboratory. Wear safety glasses and lab coat when performing the experiments. Use caution when handling the glass test tubes. Procedure Cloud in a Bottle Start by pipetting 5 ml of rubbing alcohol into the 1-L bottle. Swirl the alcohol around in the bottle; make sure to coat the sides. Place the rubber stopper in the mouth of the bottle. While holding the stopper in place tightly, pump the foot pump five times. Pull the stopper out; you will likely see a very faint pouf of a cloud. To make a better cloud, repeat the above step, but this time, pump the pump 10 times. Remove the stopper, and you should see a slightly more visible cloud. Finally, repeat again, except this time pump the pump 15-20 times. Remove the stopper, and you should see a very nice cloud.
The Ups and Downs of Thermometers Carefully pour the colored alcohol into the test tube so that the tube is almost completely full. With the help of a partner, stretch a small piece of parafilm over the top of the test tube so it is well sealed. While holding the parafilm tight with one hand and the straw with the other, carefully pierce through the plastic so the straw goes into the alcohol. About 3-4 centimeters of straw should stick out of the top of the plastic. This is your thermometer. Pour ice water into one water bottle until it is two-thirds full. Carefully lower the test tube into the ice water. Watch the straw above the plastic for about one minute, and observe what happens to the level of the alcohol in the plastic tube. Fill the other bottle with hot water until it is about two-thirds full. Carefully lower the tube into the hot water, and observe what happens to the alcohol in the plastic tube. Making Dew Use your thermometer to measure the room temperature, and record it on the card below. Fill the metal can half full with water. Put the thermometer into the can, and record the temperature of the water on the chart. Add a few pieces of ice, and stir gently with the thermometer. Continue adding ice and stirring until you see moisture form on the outside of the can. Watch closely. If you don t see any moisture forming, feel for it with your fingers. Read the thermometer the instant that you notice moisture forming on the outside of the can. Record this temperature on the chart in the area labeled Dew Point Temperature. Celsius Fahrenheit Room Temperature Water Temperature Dew Point Temperature
Try-on-your-own Activities Make Your Own Barometer Materials Wide-mouthed glass jar Balloon Rubber band Scissors Drinking straw Cardboard strip Glue Ruler Pen Paper arrow Procedure Cover the top of the jar with the balloon. Hold it in place with a rubber band. Make sure that the jar is airtight and no air can enter or escape the opening. Place a small amount of glue on the center of the balloon and place one end of the straw on the glue. The other side should extend over the edge of the jar. Stick the arrow into the side of the straw that extends over the edge. Fold a piece of cardboard so that it is able to stand upright behind the jar. On the cardboard, make a mark where the arrow at the end of the straw hits. Mark lines.5 cm on opposite sides of the original line. Write low pressure at the bottom and high pressure at the top. Place your barometer and scale in an area with stable temperature. Over several weeks, record the date, time, weather conditions and air pressure in a journal. Notice the pattern. Try making these other weather instruments and testing them out. o Anemometer - http://www.weatherwizkids.com/experiments-anemometer.htm o Hygrometer - http://www.nauticus.org/activities/pon/pon_hygrometer.html o Barometer (more elaborate version)- http://www.sci-experiments.com/barometer/ barometer.html
Student Worksheet Let s Talk About the Weather Name 1. What are the microscopic dust particles that water vapor attaches to during condensation called? Evaporation nuclei Condensation nuclei Clouds Rain 2. Temperature is a measure of the average amount of motion of molecules. True False 3. The point where temperatures cool and water vapor becomes visible is called. 4. When there is enough water vapor in the air for condensation to occur, the air is: Saturated Pressurized Condensed Precipitating 5. Weather refers to the state of the atmosphere at a specific time and place. True False
Teacher Resource Let s Talk About the Weather Follow-up Name 1. Briefly describe how clouds form. 2. Why did the red alcohol move up in the plastic tube when your thermometer was placed in hot water? 3. Briefly define dew point. 4. When there is enough water vapor in the air for condensation to occur, the air is considered to be? 5. Why is weather important to agriculture?
Careers in Agriculture