Modeling the Difficulties
you will not discharge a firearm, in this activity you will
assemble a projectile-hurling device called a potato cannon.
By analyzing the spread pattern of paint soaked projectiles,
you can observe a similar relationship between scatter and
activity page will offer:
Hands-on activity in assembling and operating a potato cannon
opportunity to emulate the work of a forensic scientist
arena for critical thinking
TEACHER NOTE: CAUTION!
students MUST wear eye protection during this investigation.
You should warn students about the dangers of inappropriate
use of this launcher, both in and out of class. Also, remind
students to use care when cutting the potato slices.
- Safety goggles
- PVC pipe section - about 1.5 feet (45 cm) long and about
a 2-inch (5 cm) diameter
- Dowel - about 2 feet (30 cm) long and narrow enough to
fit inside the pipe
- Water-based paint
- Paper targets
the Potato Cannon
- Use a knife to cut several uniform slices of raw potato.
Each slice should be about one inch (2.5 cm) thick, with
a diameter greater than that of the pipe opening (5 cm).
- Before you proceed to the next step, make sure that everyone
in the class is wearing safety goggles.
- Position a potato slice on a table. Place one end of the
pipe on top of the potato slice. Gently, but steadily, push
down on the slice so that a circular plug is cut by the
- Use the dowel to push the plug about four inches (10 cm)
into the pipe. Remove the dowel.
- Turn the pipe over and position the other end over another
potato slice on top of the table.
- Again push down on the potato to form a second plug at
the opposite end of the pipe. Use the dowel to push this
plug about one inch (2.5 cm) into the tube. Once the plug
is inserted, keep the dowel inserted in the pipe. SEE DIAGRAM.
- Obtain a handful of lentils. Coat the lentils with a thickened
layer of water based paint.
- Carefully load the lentils onto the end of the pipe opposite
the dowel (in which the plug was pushed in four inches).
This is the muzzle of your potato cannon. SEE DIAGRAM.
- Tape a sheet of white paper to a nearby wall.
- Position the muzzle one foot from this target.
- While holding the PVC pipe, push in the dowel so that
it "pops" out the other plug along with its lentil load.
SEE DIAGRAM. NOTE: Try to apply quick, even pressure when
pushing the dowel. You will need to mimic this pressure
when you repeat the activity.
- Examine the recorded scatter pattern made by the impact
of the lentils. Measure and record the circumference of
the scatter pattern.
- Repeat the activity, but this time position the loaded
muzzle two feet from the target.
- Measure and record the circumference of this scatter
- Why were two plugs of potato needed for this cannon?
- Would the cannon fire if the plugs did not form an airtight
- How did the distance to the target affect the spread of
- How does the friction between the "load" plug and the
chamber wall affect the air blast?
- Why was it important to apply the same amount of pressure
to the dowel during the two tests?
On Your Own
might the size of the projectiles affect the scatter pattern?
Think about it. Then design an inquiry strategy that would
determine if and how projectile size affects scatter. Share
your plan with your instructor. With the instructor's permission,
perform this experiment and report your results back to the
Unlike a shotgun or pistol can leave powder burns formed by
the hot gases and materials that escape from the muzzle of
the fired weapon. Explain how these burns might be used to
infer the distance between weapon and victim.
All bones are formed around a living matrix of cells. It is
these cells that repair bone fractures and injuries, and it
is the minerals deposited around living bone cells that account
for a bone's hard and inflexible characteristics. To observe
this rubbery protein structure, remove the meat from a chicken
bone. An adult can boil the bone to further remove the soft
tissue. Then, seal the cleaned bone in a jar full of vinegar.
After several days remove the bone and rinse it off in running
water. You'll observe that the bone is now soft and rubbery
and can be tied into a knot! (For a more detailed activity
about bone density, see Getting
the Minerals Out.)
A great introduction to the field of forensic science.
Wounding Factors and Effectiveness
An FBI site on handguns and the wounds they inflict.
more Web links on this topic - visit our Resources
activities in this guide were contributed by Michael DiSpezio,
a Massachusetts-based science writer and author of "Critical
Thinking Puzzles" and "Awesome Experiments in Light & Sound"
(Sterling Publishing Co., NY).
Academic Advisors for this Guide:
Corrine Lowen, Science Department, Wayland Public Schools,
Suzanne Panico, Science Department, Fenway High School, Boston,
Anne E. Jones, Science Department, Wayland Middle School,