Mathematics activities

Build a classroom balance

by

Diane L.Smith and Alan F.Smith - Tucson, Arizona

To measure the growth of your Manduca, you will need to use a balance or scale. You can build your own balance using simple materials found around your classroom or home.

You 'll need

Pencil sharpener Hole punch or wood burning tool Small hacksaw Scissors Three pencils One straight pin Two small cups (clear plastic is nice) String Block of styrofoam (about 4 " x 4 " x 1 ") Masking tape Paper clips or coins (to use as weights)

 

 

 

 

 

 

 

 

 

 

 

 

Directions

1. Sharpen two of the pencils and insert them into the styrofoam block about one-half inch apart to form 2 parallel vertical supports.
2. Push the straight pin through the erasers at the tops of these two pencils to form a bridge.
3. Use the hacksaw to cut a shallow groove across the midpoint of the third pencil. Position this pencil so that the pin is resting in the groove. This arrangement forms the arm of the balance,and the groove prevents the arm from sliding out of position.
4. Using the hole punch,make three equally-spaced holes around the top of each of the two cups (if you Íre using hard plastic cups,a drill may work be er for making the holes). Tie lengths of string through each hole and secure each cup with masking tape to the arm as shown in the drawing.Trim off any excess string.
5. Finally, calibrate your balance – add an equal number of quarters or paper clips to each cup. If the arm is horizontal, then your balance is calibrated. If not, add weight to the higher end of the arm by taping bits of tape to that end of the pencil until it 's horizontal.
6. The scale is now ready to use! Larvae and pupae can be weighed by putting the insect in one cup and balancing it with weights such as paper clips, or with standard gram or ounce weights.

Activity suggestions

Paper clips make excellent units of measure for the larger caterpillars (i.e.,5th instars). Obviously, the smaller the clip, the more distinct will be the changes in growth. What makes a good standard unit of measure? Ask students to bring in what they believe would make good standard units of measure (e.g., beads, macaroni, pennies). Visualize daily changes in weight by making a paper clip "graph". Link together paper clips of each day 's measurement to form a chain. Tack this to the bulletin board with a label. Add each day 's chain in order across the board, and soon you will have a graphical representation of growth rate.

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