Acute, right, or obtuse?
An angle is how far one arm has swung from the other. Open it slowly. The name keeps changing under you: acute, a square corner, obtuse, a straight line, and on round to a reflex.
120° obtuse
Obtuse: bigger than a square corner, but not a straight line.
Drag the end of the moving arm to open and close the angle.
Jump to a kind
Ready to try some? Types-of-angles worksheets
Where it usually goes wrong
An angle gets judged by how long its arms are drawn. Two angles of 30° look different if one is drawn with arms twice as long, and a child asked which is bigger will reliably pick the larger drawing. The arms only say where the drawing stopped. The angle is the amount of turn between them.
Try this
- Open the arm slowly through a square corner. The name changes at exactly 90° and again at 180°, and nowhere in between.
- Stop somewhere near 89° and 91°. Nothing visible happens to the corner, and the name is different — the boundary is a definition, not something the shape does.
- Keep going past a straight line into the reflex angles. Most angle worksheets never show one, so it is worth seeing that they exist.
Where this goes next
Every angle fact on top of this one — triangles totaling 180°, angles in parallel lines, the angles inside a polygon — assumes you can already see turn as a quantity.