Use a ruler and compass to construct circles, copy line segments, and draw perpendicular lines with precision.
A compass lets you draw a perfect circle. Set the compass width to the desired radius, place the pointed end at the center, and swing the pencil end all the way around.
To draw a circle with radius 4 cm, how should the compass be set?
Open the compass so the distance between the point and the pencil tip is exactly 4 cm
If a circle has a radius of 3 cm, what is its diameter?
3 × 2 = 6 cm
To copy a line segment exactly using a compass, measure its length by placing the compass point on one end and the pencil on the other, then transfer that same width to draw a new segment of equal length.
A line segment AB is 5 cm long. How would you use a compass to copy it exactly?
Set the compass to the width of AB, then use that fixed width to mark an identical length elsewhere
Why is a compass more accurate than just eyeballing a length with a ruler?
The compass locks in an exact width, removing the guesswork of reading a ruler by eye
1. To draw a circle with radius 6 cm, how should the compass be set?
2. If a circle has a diameter of 10 cm, what is its radius?
3. What tool is used to draw a perfect circle by hand?
4. A line segment is 8 cm long. What compass width would you use to copy it?
5. Why might you use a compass instead of a ruler to copy a length onto a curved or awkward surface?