铅笔是中学生常用的文具之一。利用它可以做许多物理实验,简单易行。 自制“螺旋模型” 取一张白纸,剪成直角三角形,斜边用墨水划线,直角的贴近铅笔绕在上面(如图1沿y轴绕),设螺矩为d,铅笔的圆周长为C,则推导出d=C/z·y,为 Pencil is one of the stationery commonly used by middle school students. Use it to do many physical experiments, simple and easy. Self-made “spiral model” take a white paper, cut into a right triangle, oblique side ink line, right angle of the pencil around (as shown in Figure 1 along the y axis around), set the screw pitch d, the pencil’s circumference For C, we derive d=C/z·y, which is