CCSS.Math.Content.4.MD.C.5a
The standard
An angle is measured with reference to a circle with its center at the common endpoint of the rays, by considering the fraction of the circular arc between the points where the two rays intersect the circle. An angle that turns through 1/360 of a circle is called a "one-degree angle," and can be used to measure angles.
Common Core State Standards for Mathematics
What this standard means
Students need to see an angle as a turn, not just a pointy corner. They should connect one full turn to 360 equal parts, with each part called one degree. They also need to understand that angle size depends on the amount of turn between two rays, not on how long the rays are.
Mastery looks like explaining that a 90 degree angle is one quarter of a full turn and a 180 degree angle is half a turn. Students often get stuck thinking longer rays make bigger angles, or seeing degrees as marks on a protractor instead of parts of a circle.
Ways to teach it
- Have students use two straws fastened with a brad to model quarter turns, half turns, and full turns on a paper circle.
- Ask students to write how a clock hand turning from 12 to 3 is related to 360 degrees.
- Show three angles with different ray lengths and ask students to circle any that have the same amount of turn.
- Connect angles to skateboard or scooter turns, such as a 180 turn, 90 turn, and full 360 spin.
Plan a lesson for CCSS.Math.Content.4.MD.C.5a
Generate a complete lesson plan aligned to this standard, with objectives, activities, and materials. Free, no account needed.
Related standards
- CCSS.Math.Content.4.MD.C.5b
An angle that turns through n one-degree angles is said to have an angle measure of n degrees.
- CCSS.Math.Content.HSF-TF.A.1
Understand radian measure of an angle as the length of the arc on the unit circle subtended by the angle.
- CCSS.Math.Content.8.G.A.1b
Angles are taken to angles of the same measure.
- CCSS.Math.Content.4.MD.C.5
Recognize angles as geometric shapes that are formed wherever two rays share a common endpoint, and understand concepts of angle measurement: