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HAIL STONE IMPACT
STUDENT EXPECTATIONS
Upon completion of this unit, students will be expected to know
or have an understanding of:
- How and why local convective, possibly severe, storms develop.
- How hailstones form and the conditions under which they form.
- The identification of and how to test the variables that may
influence the damage caused by hail.
- How data for various sized hailstones are collected and analyze
the impact damage with graphs.
- What atmospheric factors may affect the size of hailstones?
- How to compare and analyze insurance damage data for several
counties.
- How to test several materials for their resistance to hail damage
and explain their findings.
- The impact a severe hail storm can have on a community.
- The impact a severe hail storm can have on crops.
- The impact a severe hail storm can have on wildlife.
STATE STANDARDS
The following Colorado Model Content Standards for Science will
be met or exceeded: (Unless otherwise noted, the standards for grades
5 through 8 are used.)
Standards 1, 2.1, 2.2, 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, 6.7B, 6.8B, 6.12B,C, 6.14C,
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.RA,B, 8.5A,B,C, 8.10B, 8.12B,C
TEACHER NOTES/BACKGROUND
Usually when we think of hail, it is associated with violent thunderstorms.
In the Great Plains, the storms can be enormous systems covering
many square miles. Closer to the Rocky Mountains, the thunderstorms
are often much smaller in size. Regardless of the way they form,
these storms can develop hazardous characteristics to people, property,
and animals.
Convective Storms: These storms form when cold air masses
meet relatively warm, moist air masses and a strong convective current
develops as a result. As the warm moist air rises, it begins condensing
droplets and releasing tremendous amounts of energy. The latent
heat of vaporization of water is about 540 calories/gram. In other
words, 540 calories of heat energy is released for every gram of
water that condenses. When some thunderstorms are estimated to have
up to 200 million tons of water in them, there is almost an unimaginable
amount of energy in them! This energy increases the force of the
updraft and accelerates the development of the storm. The droplets
continue to cool and move further upward in the atmosphere where
they become supercooled. (Liquid water below 0° C)
So, how is hail formed? In general, hail is formed when
the supercooled water droplets crystallize onto a frozen raindrop
that has become suspended high up in a cloud. This may happen in
several ways. Sometimes the frozen droplets travel up and down in
the cloud growing into a layered hailstone. Other stones form while
suspended in one place, while still others form around a raindrop
that is carried high into the cloud and freezes.
Eventually the mass of the hailstone increases to the point that
the force of gravitational pull exceeds the force of the updraft
and the stone falls to the surface. Falling rain and hail create
a downdraft of cold air as they move downward. Hailstones may vary
in size from a pea to an orange, or in some rare instances even
larger. On the plains just east of the Rocky Mountains, ½
to ¾ inch diameter hailstones are common.
Early beliefs were that hailstones fell directly downward, but
subsequent research indicates that often hailstones not only travel
vertically, but horizontally in the cloud sometimes shooting out
the side of the cloud and appearing to come from a cloudless sky!
Economic impact of hail: In some regions of the country,
hail is the major cause of storm damage. Hailstones break windows,
dent vehicles, strip agricultural crops to their stems, and in some
cases have even killed livestock. A hail storm can devastate the
economy of a small farming community in just a few minutes. It can
also have a devastating affect on the hatching season of many game
birds and other wildlife.
ACTIVITY DESCRIPTION
In this activity, students will work in teams of 2 to study the
formation of convective storms and formation and structure of hail
stones. Each team will test mock hailstones of varying sizes to
investigate the impact and damage caused by hailstones. The teams
will also be required to graph and analyze the collected data.
MATERIALS
- 5 to 10 mock hailstones of various masses, and diameters. (Metallic
balls or lead shot work well, but glass or clay marbles of various
sizes can be used, but for safety should be covered with tape
or something to prevent breakage.)
- A soft grade of Styrofoam material measuring approximately 6
x 24 inches.
- Aluminum foil
- A 6 to 8 foot ladder with gravity apparatus (see drawing)
- Metric ruler and calipers if available
- A waterproof marker for labeling impact craters
- Large sheet of white butcher paper
- Activity worksheet HTML version
or
- Activity worksheet
PDF version
APPARATUS
A gravity drop apparatus can be a simple grooved piece of wood
or metal set at a slight incline so the “hailstone” will
gently roll off when released. A more elaborate spring-loaded platform
can be constructed if desired.
Set up the ladder and attach the ring stand with gravity drop apparatus
to it. .The distance to the top of the target does not have to be
exactly eight feet, as long as it is constant for all tests.
When setting up the apparatus, make certain all components are
securely fastened together. The ladder should be sturdy and in good
repair. Be certain to review proper ladder usage safety rules with
your students and supervise them appropriately.
PROCEDURE
- In this activity, you will drop a spherical "mock hailstone"
from a height of 6 to 8 ft., and determine its impact by measuring
the depth and diameter of the impact crater created in the foam.
If possible, use a gravity drop apparatus similar to the diagram.
- Cover your foam board with aluminum foil and place under platform.
- Select a "hailstone" as directed by your teacher.
- Find its mass in grams using a balance.
- If available, use a caliper to find its diameter, if no caliper
is available, use a metric ruler and measure the diameter as accurately
as possible.
- Drop your hailstone from the known height.
- Measure the diameter and depth of the impact crater formed in
the foam board.
- Record all measurements in your data table.
- Move the foam board so a non-dented area is in the target area.
- Repeat the procedures with different size and mass hailstones.
- When all data is collected, form a graph and spreadsheet (if
a computer is available) for analysis.
- If time allows drop each hailstone 5 times and record the data
each time.
- With another Styrofoam board, repeat the procedures, but tilt
the board at an angle assigned by your teacher.
ANALYSIS
Construct a line graph of the mass and crater depth of the hailstones.
Is there a relationship illustrated by this graph?
Construct another graph with actual diameter and crater diameter.
Is there a relationship illustrated by this graph?
Explain some similarities and differences from real hail and the
"mock hail".
CONCLUSIONS
Discuss or have students write up what it would be like to have
many of the "hail dents" in a single square foot. As an
extension, you might have them call an insurance agent for annual
damage figures from your city/county/state due to hail. Discuss
or have students find out what part of the year do most hail storms
happen and why. Have them decide if a steep pitched roof would be
less likely to sustain damage from hail or more damage. Ask them
what happens to livestock and wildlife during a hail storm. You
might want them to discuss or research what type of building materials
for roofs would be damaged most or least.
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