Parts of a circle
Nine names, each drawn on its own circle so the picture can be matched rather than the sentence remembered — including the four pairs that get mixed up.
Reference chart
Parts of a circle
Center
The exact middle
Radius
Center to edge
Diameter
Across the center
Chord
Edge to edge, off-center
Circumference
The whole way round
Arc
Part of the way round
Sector
The slice of pizza
Segment
A chord and its arc
Tangent
Touches at one point
Everything here is measured from the center. A radius reaches it, a diameter crosses it (so d = 2 × r), a chord misses it, and a tangent never touches the inside at all.
What's on this chart
The usual version of this page is one circle with nine leader lines pointing at it. That answers the question "what is this line called", which is not the question a child arrives with. They have been told to find the sector, or to measure a chord, and what they need is to know which part of their own circle that is. So every name here gets a circle of its own, and the page is used by matching rather than by reading.
Why this chart helps
Four of the nine are only ever confused with one other, and they are drawn to be told apart. A chord and a diameter are the same kind of line — both join two points on the edge — and the only difference is whether it passes the center, so the center dot is marked on both drawings and the diameter runs straight through it. A sector and a segment are the same region cut two different ways: the sector keeps its two radii and is the slice of pizza, the segment has the chord straight across and is the crust without the point. Side by side that difference is visible before a word is read.
More printable charts
- Naming 2D shapes
Print Count the straight sides on a shape, then read its name below it. - Quadrilateral family
Print Follow the branches to see which names a shape inherits. - Lines of symmetry
Print Fold each shape in your mind and count the matching halves. - Types of angles
Print Find the picture that matches yours, and the name is under it. - Angles in parallel lines
Print Match each numbered pair to its position around the transversal. - Perimeter formulas
Print Follow the traced edge on the figure, then read the formula under it. - Area formulas
Print Match your shape to a figure and use the letters drawn on it. - Volume formulas
Print Find your solid, then multiply the base area by how tall it stands.