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DO NOW
DO NOW
Try this: Draw two line segments that are perpendicular to each other (90 degrees) and that bisect each other (cut each other in half). An example of this is the coordinate plane (X-Y axes). Try to draw this as exactly as possible.
Try this: Draw two line segments that are perpendicular to each other (90 degrees) and that bisect each other (cut each other in half). An example of this is the coordinate plane (X-Y axes). Try to draw this as exactly as possible.
LEARNING TARGET
LEARNING TARGET
I can explain how to use a compass and straight edge to draw a precise perpendicular bisector, and to bisect an angle.
I can explain how to use a compass and straight edge to draw a precise perpendicular bisector, and to bisect an angle.
I DO
I DO
Do you want your drawing kits? Let's talk a little first ...
Safety: compasses are sharp on one end. When we are using drawing kits, be mindful of how you're moving and the people around you.
Safety: compasses are sharp on one end. When we are using drawing kits, be mindful of how you're moving and the people around you.
Care of Tools: compasses are precision instruments. If they become bent or loose, they will no longer work properly. So you can see through them, the straight edge (and other tools) are clear plastic. Take care not to break or drop them.
Care of Tools: compasses are precision instruments. If they become bent or loose, they will no longer work properly. So you can see through them, the straight edge (and other tools) are clear plastic. Take care not to break or drop them.
Storage of Tools: when you're done with a particular tool (and at the end of the class), carefully return all pieces to their storage case, and return your case to the bin.
Storage of Tools: when you're done with a particular tool (and at the end of the class), carefully return all pieces to their storage case, and return your case to the bin.
Let's get our kits!
What's in there?
2 drawing compasses (one takes a pen or pencil, the other has built-in lead).
Eraser, extra lead, pencil sharpener, pencil
Straight edge (AKA a ruler)
Protractor (for drawing angles)
2 triangles (for drawing certain angles and triangles)
WE DO
WE DO
Get out one of the compasses (your choice) and the straight edge. Let's talk about how it works.
Get out one of the compasses (your choice) and the straight edge. Let's talk about how it works.
Make sure the point of the compass and the tip of the pencil or lead are lined-up when the compass is all the way closed. Take care not to force any part of the compass, particularly the knobs used to tighten the pencil or lead. These should be tight, but not so tight that you strip the screw.
At its most basic, a compass is used to draw perfect circles. To do this, the needle point goes where you want the center of the circle to go. The pencil will draw the circle around that point. Let's try drawing our first circle. Open the compass about halfway, put the needle point in the center of your paper.
Hold onto the leg of the compass with the needle point (not the one with the pencil) and rotate it around with the pencil lightly touching the paper. Alternatively, hold the compass and spin the paper. When you get back to the start, your lines should meet exactly.
YOU DO
YOU DO
How do you use a compass to create a perpendicular bisector?
How do you use a compass to create a perpendicular bisector?
Draw a line about 4 inches long in the center of a paper with the straight edge
Adjust your compass so it's a little more than half as wide as your line
Place the point of the compass on one end of your line, and draw arc segments above and below the line
Repeat step 3 on the other end of your line
Use your straight edge to connect the intersections of the two sets of arcs. You did it!
Straight edge tip: Put your pencil on the point you want to connect, and move the straight edge against the pencil. Repeat on the other side.
Here is an animation of this in action.
How do you use a compass to bisect an angle?
How do you use a compass to bisect an angle?
Use your straight edge to draw two lines that form an acute angle
Adjust your compass so it's about halfway through your angle and draw an arc that intersects both rays of the angle (with the point at the vertex)
Place the point of the compass on the intersection of the arc with one of the rays, and draw an arc segment outside of the ray
Repeat step 3 on the other intersection
Use your straight edge to connect the intersections of the two arc segments with the vertex of the angle. You did it!
Here is an animation of this in action.
Practice these two processes, and turn in your best version of each one for a 3. For a 4, Get creative and use these two processes together to create something unique (make sure you are correctly using both processes still).
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