Using Experiments To Teach Agriscience

Glen Miller

The Agricultural Education Magazine, April 1996, Volume 68 Issue 10, p. 6-8.

YOU ARE DIFFERENT!!!! YOU ARE UNIQUE!!! STUDENTS LIKE TO COME TO YOUR CLASS!!! STUDENTS LEARN FROM YOU!!!! STUDENTS REMEMBER WHAT YOU TEACH!! STUDENTS APPLY WHAT YOU TEACH TO THE REAL WORLD!!!

Many teachers are really worried about increased science being integrated into the agricultural education curriculum. They ask themselves "What will keep the principal from replacing me with a science teacher?" Relax, you really are different, and what makes you so special is what makes agricultural education so special - it is real.

Experiments in agriscience are old and they are new. They are as old as seeds wrapped in paper towels to check germination rates, and they are as new as recombinant DNA.

This is not new. We have always taught the scientific principles which form the foundation of agricultural mechanics. We have not always named the principle for the student. Agricultural mechanics is a perfect vehicle to teach physical science. Scientific experiments are directly translated into applications in agricultural mechanics. I would like to share some experiments I find useful in teaching scientific principles through agricultural mechanics. One experiment that develops student interest and can be directly translated into an agricultural mechanics wood construction activity, is the holding power of different fasteners. In this experiment, I assemble several different stud and plate configurations using glue, 8 penny smooth box nails in a toenail configuration, and 16 penny smooth box nails nailed on an end grain basis

The lumber is placed in a device developed by Dr. Clinton Jacobs. This device consists of a lever arm that has a fulcrum with a 10 inch to 4 inch ratio. The end of the lever arm has a 1/2 inch square hole which accepts the drive end of a torque wrench. A bending beam type foot pound torque wrench is then placed in the hole and the lumber is pulled apart

Allow the students to predict the force required to destroy the joints. Students will almost always assume the nail joint will be the strongest. In the test done for the photographs in this article, the 8 penny toe nail joint read 70 foot pounds on the torque wrench while the 16 penny end nailed joint produced 100 foot pounds and the hot glue joints require a pressure of 145 foot pounds. (Note: Be careful if you choose to duplicate this experiment. The glue joint will fail forcefully without warning.)

Another effective translation of physical science in agricultural mechanics was created

by Dr. Phillip Buriak. Dr. Buriak developed an outstanding exercise in the conservation of energy that can be translated into power train exercises on production or horticulture machinery. In this experiment. students can visualize gear ratios and speed on a familiar ten speed bicycle.

By placing an inch pound torque wrench on each axle, the input and output torque of the ten speed can be measured through all ten gears. Students can then directly observe the relationship between a speed ratio and torque ratio. The principle of the conservation of energy is revealed on a familiar speed bicycle. Dr. Buriak has included this activity is thc book he co-authored with Edward W. Osborne entitled Physical Science Applications in Agriculture (1996) published by Interstate Publishers, Inc., Danville, Illinois.

The scientific principle underlying the practical use of electricity is a mystery to many. Students have great difficulty visualizing magnetic lines of force and the induction of current in conductors. One experiment that helps students visualize magnetic lines of force is the placing of a bar magnetic on the screen of your overhead projector. Place a piece of acetate over the magnet and turn the projector on. Sprinkle iron filings or shavings out of the metal cutting band saw on the acetate. The filings will align themselves with the magnetic lines of force. Dr. James A. Walters published a terrific experiment in the May 1990 issue of the School Shop (Tech Directions) magazine. In his experiment, he constructed a device consisting of four pieces of copper pipe placed one inside of each other. The pipe sizes are 1 1/4 inches, I inch, 3/4 inch, and 1/2 inch by 36 inches in length. The pipes are placed one inside the other with short lengths of 14 gauge copper wires used as spacers and soldered in place.

The experiment consists of dropping a cow magnet (purchased from a veterinary supply house) through the inner most pipe. Then drop a piece of 1/2 inch cold rolled steel cut and shaped to resemble the cow magnet. Students will immediately notice the difference in speed between the cow magnet and the piece of 1/2 inch mild steel.

The obvious question to ask the students is WHY? Why does the magnet fall at a slower rate than the mild steel. The magnet falling through the copper pipe induces a current in the pipe. It is the same scientific principle involved in the generation of electricity, the operation of an electric motor, the ability of a coil to step up or step down electricity. As the current is induced. a magnetic field is also created which is the same polarity as the magnet. The magnet is repelled by the magnetic field it is creating.

A very simple experiment can be used to illustrate several important scientific principles. The operation of a Venturi is a concept that is easily demonstrated with a soda straw, a cup of water, and in air Source.

The air is discharged across the top of the tube at a high speed, just as a venturi in a carburetor speeds the air above the tube that reaches into the gasoline Supply. The effect is the same, but much less flammable.)

This same experiment can be used for thermodynamics illustrations. The mist coming from the tube immediately cools the air in the area. This mist can be safely directed toward students to illustrate the principle of evaporative cooling. As the water changes to a gas, it absorbs heat. As refrigerants evaporate inside an evaporator, they also absorb heat. You can probably think of other experimental uses for this activity.

Other experiments I find useful include the principle of work. Using a tool box, I call a student forward to lift the tool box. The student is asked to hold the tool box, and the other Students are asked to tell me what is happening. It is relatively easy to get the concept that the student holding the tool box is applying force to the bottom of the box. The concept of work follows when then students think through the process of lifting the tool box from the floor. Two measurements are then taken, the weight of the tool box and the distance it was lifted. You and the students can then compute the foot pounds (distance x weight) required to move the box.

The concept of torque is also easily illustrated in a humorous way. Ask a student to come forward and hold one end of an eight foot 2 X 4. The instructor can then use a spring scale, such as a fish scale, to place a load on the far end of the 2 X 4. Instruct the student to resist the effort to twist. Of course, the leverage of the 2 X 4 easily overcomes the strongest student. only a few pounds of force is required to twist the student.

A wealth of experiments exists that make teaching exciting. A great way to share your teaching experiments is through our professional organization and the Ideas Unlimited Contest. Take a moment today and share one of your great teaching experiments with someone else.