MAKING LAYERED HAIL STONES IN THE CLASSROOM
Teacher Notes
The idea that a hail stone is layered because it has made several trips up and down in a cloud is sometimes a hard concept for students to understand. To add to the confusion, the idea of super cooled water attaching itself to a nucleus to make the hail stone larger really boggles some students down.
I have tried several ways to demonstrate the above concepts without much success. This is an experiment that I have worked on with some success, and will welcome any suggestions or improvements to make the demonstration better. Since dry ice is used, you might want to do it as a demonstration or a lab for your students. You know your students and how safe they are.
A different twist to this is to use different flavors of fruit juices or to use colored water instead of water. (Kind of a wild way to spice up a punch bowl would be to have different layered ice cubes with different flavors and colors!)
MAKING HAILSTONES IN THE LAB
STUDENT EXPECTATIONS:
Upon completion of this activity, students will be expected to have a better understanding of:
How hail forms in the atmosphere.
Why hailstones are layered
What accretion is.
What supercooled liquids are.
STATE STANDARDS:
The following Colorado Model Content Standards for Science wil be met or exceeded: (Unless otherwise note, the standards for grades 5 through 8 are used.)
Standards: 1, 2.1, 2.1, 3.1, 3.2, 4.1, 4.2, 4.3, 5 and 6
The following TEXAS Essential Knowledge and Skills for Science will be met or exceeded: (Unless otherwise noted, the TEKS for middle school science are used.)
6.7A,B, 6.2A,C,D,E 6.3A,B,C,D, 6.4A,B, 7.8B, 6.12B,C 7.1A,B, 7.2A,B,C,D,E, 7.3A,C,D, 7.4A,B, 7.12C, 7.14A,B, 8.1A,B, 8.2A,B,C,D,E, 8.3A,C,D,E, 8.4A,B, 8.5A,B,C, 8.10B, AND 8.12B,D
ACTIVITY NOTES
Hail stones are formed when supercooled water collects on a nucleus which is many times an ice crystal that grows larger by accretion. The nuclear particle will be carried upward in the cloud by updraft winds, collecting more supercooled water, thus causing the nucleus to grow larger. Each time the nucleus stone is carried upward the stone accretes more and more water which freezes on impact with the stone. A layered ring forms around the sone, almost like the growth rings on trees. The updraft winds are very powerful and the hail stone grows even larger sometimes than a softball. When the hail stone becomes too heavy to overcome these strong winds, it falls to Earth sometimes at speeds exceeding 80mph causing extreme damage, and possible death to wildlife, crops, livestock, and in rare cases people.
Supercooled water or supercooled liquid is when a substance is cooled below its normal freezing point and remains a liquid. This usually happens in an area of low pressure and where the substance has no nuclei to freeze on. The more pure the water is and the smaller the particle is, the easier it is to become supercooled. When a supercooled liquid comes into contact with another surface, it instantly solidifys.
Accretion is the process of an object to gather material on its outside layer becoming larger and more dense. ( Hail accretes supercooled water on its outside layer and the stone becomes larger.)
MATERIALS
About ½ pound of dry ice 2 Large Styrofoam cups Gloves
Marble, bb, or dice (Stone nuclei) Water
String Pen or pencil
Super glue Towel
(OPTIONAL MATERIALS)
Food coloring 2 Large Styrofoam cups for each color or juice
OR
Various colors of fruit juices
METHODS
1. Place one of the Styrofoam cups inside the other. (This helps insulate your hail making system.)
2. Pour about 300ml water in the cups
3. Attach a 6 to 8 inch string to your nuclei with super glue being careful to not get super glue on yourself nor your clothing
4. Place your stone nuclei on the block of dry ice and press it down on the block with a towel for about one minute, being careful to not put your unprotected skin on the dry ice.
5. Place a small piece of dry ice (about 1 cubic inch) in the cup of water. (Use gloves or tongs when handling dry ice!)
6. Use the string attached to the nuclei to hold on to the nuclei, then dip the nuclei in the cold water in the cup for about 5 seconds and immediately place it back on the dry ice for about 30 seconds.
7. Repeat step 6 10 times.
8. Let the nuclei set on the dry ice about 3 minutes, and start step 6 and 7 again for the next layer. If you have used optional materials, now is the time to change colors, as this begins a new layer of accreted ice on your hail stone.
9. Repeat the procedure for as many layers of ice you can get on your hail stone, or as directed by your instructor.
RESULTS
(Answer in complete sentences and proper grammar.)
1. Did your nuclei accrete and freeze water to it?
2. If not, explain why you think it did not work for you.
3. If the answer to #1 is yes, about how much larger did your stone become?
CONCLUSIONS
(Yes, these must be in complete sentences with proper grammar too.)
1. What is meant by a supercooled liquid?
2. Give an example (other than a hail stone) of something that goes through an accretion process.
3. Explain how this lab exercise demonstrated how a hailstone increases its size in the atmosphere.
4. Why do some hail stones get much larger than others?
5. List five precautions you should take if you are threatened by a hail storm.
A.
B.
C.
D.
E.
6. Explain how this lesson and activity may have helped you better understand how hail is formed.