L2 · Angles as motion: arms, vertex, rotation

Learning goal

“I can name the parts of an angle - two arms that meet at a vertex - and I can describe an angle as a turn: one arm stays still while the other rotates around the vertex.”

Arm — one of the two lines that form an angle. Arms can be line segments or rays.

Vertex — the point where the two arms of an angle meet.

Rotation — a turn around a point. An angle can be the amount of rotation of one arm around the vertex.

Hinge — a joint that lets one part turn around a fixed point, like the hinge of a door. A hinge works like a vertex.

Worked example

Two sticks are joined at one end by a pin. Step 1: The two sticks are the arms of the angle. Step 2: The pin end - the one point where both arms meet - is the vertex. Step 3: The opening between the sticks is the angle itself. The vertex is just the meeting point; the arms are just the sides. The angle is the OPENING. Say it plainly: arms make the sides, the vertex is the corner point, and the angle is the opening between the arms.

Check yourself — explain it

The vertex of an angle is...

Paired problem — example still visible

A gate hangs from a post. The gate turns on the post. Which part works like the vertex? -> The post (the fixed point the gate turns around)

Faded completion — last step is yours

"Two arms meet at a ___. The opening between the arms is the ___" -> vertex; angle

Ready to practise?

10 scored questions with a 3-rung hint ladder. Mastery needs 8/10 plus both gate questions.

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