Ward’s Convection Currents Lab Procedure – Part 1

Setup A1. Before beginning, fill the 250mL beaker with tap water and heat it up on the hotplate. Set the hot plate to 5. 2. Fit two plastic lids on each of 4 Styrofoam cups. Set the clear plastic box onto the four Styrofoam cups as shown

in Figure 1. Carefully fill the box with cold tap water to within 3-4cm from the top. Let the water become calm before proceeding.

Figure 1

3. Using the pipette, carefully place 3 spots of red food coloring onto the bottom of the box as show in Figure 1. Insert the pipette all the way down to the bottom of the box before squeezing out the dye. Each spot should be about 2-4 cm in diameter. Try to minimize disturbing the water as you insert and remove the pipette.

4. Take the beaker of hot water from step 1, and using tongs, carefully pour some water into a Styrofoam cup and position it beneath the center dye spot in the box. The plastic lid spacers you fitted on the corner cups should provide you with enough clearance to gently slide the cup with hot water under the spot. Keep the beaker set to the side to the cool down, and turn off the hotplate so it can cool down as well.

5. Now position yourself so you can view the box from the side at eye level, and observe what happens to the 3 spots over the next 5 minutes. Be sure to look for changes in all 3 spots. Write you observations on your lab sheet.

6. Sketch what you observed on Diagram 1 on your lab sheet. Use arrows to show the direction of flow.7. Using two hands under the box, carefully empty the water into a sink and begin Setup B.

Setup B1. Before beginning, fill the 250mL beaker with tap water and heat it up on the hotplate. Set the hot plate to 5.2. Setup the box and cups just like in Setup A. Add three spots of red food coloring just like Setup A as well. 3. This time, fill two Styrofoam cups with hot water and position them beneath the two outside spots. Observe

what happens over the next 10 minutes, and then sketch what you observed in Diagram 2 on your lab sheet. Be sure to look for changes in the middle spot. Use arrows to show direction of flow.

4. Carefully empty the water from the box into a sink, and begin Setup C.

Setup C1. Before beginning, fill the 250mL beaker with tap water and heat it up on the hotplate. Set the hot plate to 5.2. Set up the plastic box once again as in Setups A and B and fill with cold tap water to within 3-4 cm from the top.

Let the water become calm. Next, place two spots of food coloring near one end of the box.3. Fill two Styrofoam cups with hot water and position one cup full of hot water beneath each spot.4. Use a plastic spoon to obtain a blue ice cube from your instructor. Carefully set the cube into the water at the

opposite end of the box from your dye spots. Use the spoon to steady the ice cube until it stops moving.5. Position yourself at eye level with the side of the box, and observe the water as the ice cube melts. Sketch your

observations in Diagram 3 on your lab sheet. Use arrows, once again, to indicate flow direction.

Ward’s Ocean Currents Lab Procedure – Part 21. Before beginning, fill the 250mL beaker with tap water and heat it up on the hotplate. Set the hot plate to 5.2. Set up the clear plastic box as shown in Figure 2. Place the wood block at one end to incline the box.3. Add about 800 mL of room temperature water to the box (from your tan buckets). Let the water become calm

before proceeding.4. Next, place 25mL of room temperature water in a small beaker. Add one level teaspoon of salt and one drop of

yellow food coloring to the water and stir until the salt dissolves. Carefully and slowly pour the solution into the raised end of the box as shown in Figure 3. Position yourself at eye level along the side of the box, and observe what happens to the solution. Describe what occurs on your lab worksheet.

5. Place 25mL of ice water in a beaker, and stir in a drop of blue food coloring. DO NOT POUR IT INTO THE BOX YET! Predict on your lab worksheet what will happen when you pour the blue ice water into the box.

6. Now, carefully and slowly pour the blue ice water into the raised end of the box. Describe what happens on your lab worksheet.

7. Rinse and refill your beaker with 25mL of hot water, and stir in a drop of red food coloring. Predict what will happen when this solution is poured into the box on your lab worksheet.

8. Carefully and slowly pour the hot water into the raised end of the box. Describe what happens on your lab worksheet.

9. Next, add a level spoonful of salt and a drop of green food coloring to 25mL of ice water. Stir until the salt dissolves, and then carefully pour the solution into the box as you did with the other solutions. Describe what happens on your lab worksheet.

10. Use colored pencil to fill in Diagram 4 on your lab worksheet, showing the relative positions of each of the solutions in the box following these steps.

Ward’s Coriolis Effect Lab Procedure – Part 31. Tape a Northern Hemisphere projection map to the turntable. Have one person spin the map

counter clockwise. Have another person take the red pen and try to draw a radius from the North Pole outward to the edge of the projection on the turntable while the map is spinning. Just draw it straight (your pen should curve). Repeat with the blue pen but this time start at the equator and draw the straight radius in towards the North Pole.

2. Tape a Southern Hemisphere projection map to the turntable. Have one person spin the map clockwise. Have another person draw a radius with the black marker from the South Pole to the equator. Repeat with the green marker from the equator the South Pole. Sketch your drawings in your lab worksheet.

Describe how these marker paths represent a. the direction of air mass flowing from the North Pole toward the

equatorb. the direction of air mass flowing from the South Pole toward the

equatorc. the direction of air mass flowing from the equator toward the

North Poled. the direction of air mass flowing from the equator toward the

South Pole

This part will be done as a class – watch the following videos and take notes on your lab handout.Video 1: https://youtu.be/iv5WL1W4-WI Video 2: https://www.youtube.com/watch?v=mcPs_OdQOYU&feature=youtu.be Video 3: https://www.youtube.com/watch?v=i2mec3vgeaI&fbclid=IwAR17hWUZnfNSNUIE_KSTU7rNQWISvWZJzajaSyXYASvY4XwYx-31g6CIRoI

Name: ___________________________________________ Date: ______________________________ Period: _______

Ward’s Convection Currents Lab – Student Worksheet

Part 1: Convection CurrentsThe earth’s atmosphere is heated in several ways by the transfer of energy from the sun. All of the energy that

the earth receives from the sun travels through space as radiation. Radiation is the transfer of heat energy in the form of infrared rays. When the oceans and land surfaces absorb some of the sun’s energy, in the form of ultraviolet rays, it is radiated back from the earth to the atmosphere in the form of infrared rays. These infrared rays cannot pass through the atmosphere into space, but are instead trapped by carbon dioxide and other atmospheric gases which absorb them. This process is called the “greenhouse effect” and helps to form a kind of heat blanket around the earth.

While radiation is responsible for atmospheric heating, some heating is due to conduction and convection. In conduction, heat energy is transferred directly from one substance to another by contact. As the molecules are in a substance are heated, they move faster.

Air heated by radiation or conduction becomes less dense and rises. The cooler, denser air above it begins to sink. As it does so, the cooler air pushes the warmer air upward. At the same time, the sinking cold air is now warmed by its proximity to the earth’s surface and begins to rise. This continuous rising and falling of air forms convection currents.

Since warm air is less dense than cool air, it also exerts less pressure on the earth than an equal volume of cooler air. As a result, the atmospheric pressure beneath a warm air mass is generally lower than the pressure below a cold air mass. When a dense, cool air mass moves into a region of low pressure, it forces the warmer, less dense air upward. In general, cool air is always moving towards areas of lower pressure. These pressure differences in the atmosphere are the result of the unequal heating that causes convection, and ultimately create the conditions behind the formation of winds and the general movement of air worldwide.

Pre-Activity Questions1. If one beaker contains 100mL of cold water, and another contains 100mL of hot water, which beaker contains

more molecules? Why?

2. Atmospheric pressure is the pressure exerted on the earth by the force of gravity pulling the air towards the earth’s surface. Where air is rising from the surface, will the atmospheric pressure be increased or decreased? Why?

Activity Observations – Setup A5. Now position yourself so you can view the box from the side at eye level, and observe what happens to the 3

spots over the next 5 minutes. Be sure to look for changes in all 3 spots. Write you observations here:

6. Sketch what you observed on Diagram 1 below. Use arrows to show the direction of flow.

Diagram 1

Activity Observations – Setup B3. Observe what happens over the next 10 minutes, and then sketch what you observed in Diagram 2 below. Be

sure to look for changes in the middle spot. Use arrows to show direction of flow.

Activity Observations – Setup C5. Position yourself at eye level with the side of the box, and observe the water as the ice cube melts. Sketch your

observations in Diagram 3 below. Use arrows, once again, to indicate flow direction.

Post-Activity Questions1. The house pictured here in Figure 3 has a glass “sun space” attached to its south side. Vents allow air to flow

from the house into the sun space, and vice versa. Put several arrows on the dashed line to show the direction the air will flow as the air in the sun space is warmed by the sun.

2. Which situation would result in a decrease in atmospheric pressure at the earth’s surface? (Circle one)Air gets hot and begins to rise OR Cold air is sinking to the surface

3. Go back to the three diagrams you constructed for the lab. Label the spots in each diagram that became areas of lower pressure.

4. From your knowledge of onshore and offshore breezes, explain why the wind would blow in from the sea toward the land during the afternoon.

Diagram 2

Diagram 3

5. A “monsoon effect” may happen in the summer as air over a continent becomes much warmer than air over the ocean. Fill in the blanks in the following statements:

As air over the continent becomes hotter, it will begin to ____________ (sink, rise). This causes

___________________ (lower, higher) pressure over the continent. The flow of air will be

___________________ (away, toward) the center of the continent.

Part 2: Ocean Density CurrentsAnyone visiting the seashore is struck by the constant motion of water traveling on the surface of the ocean in

the form of waves. But beneath the surface, water is also moving in giant streams called currents. All ocean currents are derived from the same major factors: wind patterns and differences in water density.

There are two principal types of currents: surface and deep. Surface currents usually have a depth of several hundred meters and are driven by global wind patterns. In contrast, deep currents move slowly at a depth beneath the surface of the ocean and are driven mainly by differences in water density.

The water density is affected by changes in temperature and salinity. The large amounts of dissolved solids in ocean water make it more dense than pure freshwater. Salinity is the term used to describe the amount of dissolved solids in the water, since most of these solids are in the form of salts. As salinity increases, so does the density of the water.

Temperature also affects the density of ocean water, with the density increasing as the water grows colder. When water is cooled, it contracts and its molecules are crowded more closely together. As a result, the water becomes more dense and sinks. The temperature of ocean water is basically determined by the amount of infrared radiation it receives from the sun. The densest ocean water is found in the cold temperatures of the polar regions, whereas waters in equatorial regions heat up, expand, and become less dense. These equatorial waters, driven by surface winds, tend to flow towards the poles. One their way there, the waters carried by surface currents return to the atmosphere a large portion of the heat accumulated in the tropics. When large masses of water of unequal densities meet, they generally do not mix.

Activity Observations – Part 24. Position yourself at eye level along the side of the box, and observe what happens to the solution. Describe

what occurs:

5. Place 25mL of ice water in a beaker, and stir in a drop of blue food coloring. DO NOT POUR IT INTO THE BOX YET! Predict what will happen when you pour the blue ice water into the box.

6. Now, carefully and slowly pour the blue ice water into the raised end of the box. Describe what happens:

7. Rinse and refill your beaker with 25mL of hot water, and stir in a drop of red food coloring. Predict what will happen when this solution is poured into the box:

8. Carefully and slowly pour the hot water into the raised end of the box. Describe what happens:

9. Next, add a level spoonful of salt and a drop of green food coloring to 25mL of ice water. Stir until the salt dissolves, and then carefully pour the solution into the box as you did with the other solutions. Describe what happens:

10. Use colored pencil to fill in Diagram 4 on your lab worksheet, showing the relative positions of each of the solutions in the box following these steps.

Post-Activity Questions1. How would an increase in evaporation affect the density of ocean water?

2. Which would contain more water molecules – a beaker containing 100mL of hot water or a beaker containing 100mL of cold water? – Explain.

3. When seawater freezes in polar regions, most of the salt is left behind. How would this effect the density of the water that is left unfrozen?

Part 3: Coriolis EffectRemember that Earth is not still - it rotates. The movement of wind is affected by the rotation of Earth. Because of this, winds do not blow directly north or south. The Coriolis effect causes the winds to change direction; winds in the Northern Hemisphere curve to the right while winds in the Southern Hemisphere curve to the left. Record your observations from the turntable activity below:

Describe how these marker paths represent a. the direction of air mass flowing from the North Pole toward the equator

b. the direction of air mass flowing from the South Pole toward the equator

c. the direction of air mass flowing from the equator toward the North Pole

d. the direction of air mass flowing from the equator toward the South Pole

Take notes from the videos below:

To Summarize: Global winds appear all over the world because of the following reasons: 1. Uneven heating of the Earth's surface, 2. Pressure differences, 3. Coriolis Effect