Plane Figures: Positions of a Straight Line

Age
6-9.

Materials

 * A transparent pitcher and vase
 * Water
 * Red dye
 * A level, two plumb lines, with a red line (cord)
 * A red stick
 * A globe

Presentation

 * 1) Dye the water in the pitcher red (because red is always used to highlight the subject of a presentation) and pour some into the vase, which is placed in the center of the table.
 * 2) Observe the surface of this water and describe it: it is still.
 * 3) This will be a point of reference.
 * 4) Agitate the pitcher and place it next to the vase.
 * 5) Let's wait without saying anything until the surface of this water becomes like the other.
 * 6) When it is exactly like the point of reference, the surface can be identified as horizontal.
 * 7) Place the red stick alongside the vase so that it aligns perfectly with the water.
 * 8) This stick represents a line which goes on in both directions.
 * 9) When it has the same position as the surface of the still water, it is a horizontal line.
 * 10) Drop the stick in the water and wait until it is still (like the point of reference).
 * 11) This stick represents one of the lines that make up the surface of the water.
 * 12) This is a horizontal line.
 * 13) Remove the stick.
 * 14) A straight line is horizontal when it follows the direction of still water (horizontal &lt; horizon: Greek horizon &lt; horas, boundary, limit; thus the horizon is the boundary of the visible earth in all directions, where it seems that the sky touches the water.
 * 15) Bring the children up the hill to see the horizon.
 * 16) Hold the plumb line until it is still.
 * 17) This will be the point of reference now.
 * 18) Get another plumb line and wait without touching it, without a word, until it is exactly like the point of reference.
 * 19) Place the red stick along the red cord, so that it coincides just as the stick on the surface on the water.
 * 20) This straight line which goes on in both directions infinitely is vertical, because it follows the direction of the plumb line.
 * 21) This is a vertical line (vertical: Latin verticalis &lt; vertex, whirlpool, vortex, crown of the head, summit, highest point, &lt;vertere, to turn; therefore vertex can be applied to anything which turns like a whirlpool, or to the highest point, like the crown of the head or the summit).
 * 22) A vertical line is one which points to the vertex, that is, the topmost point in the sky over our heads (zenith).
 * 23) It passes through the center of the earth and on to the nadir (opposite of zenith).
 * 24) Take the plumb line and hold it still again.
 * 25) Let's imagine that this is a straight line which goes on in both directions - up to the zenith and down through the center of the earth to the other side.
 * 26) Use the globe to show that a vertical line is relative to the position of the observer.
 * 27) Place the points of reference for the two opposite elements in front on the child.
 * 28) What is the median? Hold the red stick horizontally.
 * 29) When a straight line follows the direction of the surface of still water, what is it? A horizontal line.
 * 30) Hold the stick vertically.
 * 31) When a straight line follows the direction of the plumb line what is it? A vertical line.
 * 32) Hold the stick obliquely.
 * 33) Is this straight line like the surface of water? The plumb line?
 * 34) When a straight line is neither horizontal or vertical, it is oblique.
 * 35) Turn the stick 360o identifying its position as it turns - horizontal, oblique, oblique, oblique....vertical, oblique, oblique, oblique, oblique, horizontal, oblique ...etc. (oblique: Latin obliquus, slanting, sloping, not straight, not right, devious)
 * 36) So what is straight, right, and normal?
 * 37) The horizontal and vertical line.
 * 38) The oblique line runs contrary to the true, contrary to vertical or horizontal.

Variation
Classified nomenclature and commands. Demonstrate use of the level for determining lines in the environment.