Compass (drafting) Facts for Kids

Using a compass to draw a circle

A compass is a handy tool used for drawing perfect circles or parts of circles called arcs. You can also use it to measure distances, especially on maps. Compasses are useful in many areas like mathematics, drafting, and navigation.

Most compasses are made of metal. They have two main parts, called legs, that join at a hinge. You can move these legs closer or farther apart to change the size of the circle you want to draw. One leg has a sharp, pointy part called a spike. The other leg holds a pencil or a pen.

There are two main types of compasses:

Mechanical compass: This type uses a mechanical pencil.
Normal compass: This type holds a regular pen or pencil.

To make the compass work well, you need to adjust how much the pencil or pen sticks out.

A divider is a special type of compass. It has two legs, and both ends have a sharp spike. Dividers are used to measure distances or lengths. They are called dividers because they can help you divide a larger distance into smaller, equal parts using geometry.

How to Use a Compass
Compasses in Geometry
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How to Use a Compass

To draw a circle, first press the leg with the spike firmly into the paper. Then, place the pencil or pen tip on the paper. Carefully move the pencil around in a full circle. It's important not to change how far apart the legs are while you are drawing. You can make a circle bigger or smaller by moving the legs farther apart or closer together before you start drawing.

You can also use dividers to measure distances on a map. First, set the distance between the two spikes on the divider to match a known distance on the map's scale. Then, you can use the divider to "walk" along a path on the map. By counting how many times the divider fits along the path, you can figure out the real distance.

Compasses in Geometry

In plane geometry, which is about shapes on a flat surface, people use "compass and straightedge" drawing. This means you only use a compass to draw circles and a straightedge (like a ruler without markings) to draw straight lines.

While real compasses are used on paper, the compass used in proofs in geometry is an imaginary, perfect tool. This ideal compass draws perfectly accurate circles. One idea of this perfect tool is the "collapsing compass." It can draw a circle from a certain point with a certain radius, but then it "collapses" and cannot be used to draw another circle of the same size without resetting it. This is different from a real compass, which can draw many circles of the same size without being reset.