Shape and Space - Lines and Angles (Acute, Obtuse, Right, Straight, Reflex)

An angle is formed when two rays or line segments meet at a common endpoint called a vertex. The size of the angle is measured in degrees ($^{\circ}$) using a tool called a protractor. Visually, you can think of an angle as the amount of 'turn' between two lines.

Acute Angles are those that measure more than $0^{\circ}$ but less than $90^{\circ}$. Visually, these angles appear 'sharp' or narrow, similar to the tip of a pencil or a partially opened pair of scissors.

Right Angles measure exactly $90^{\circ}$. These represent a perfect quarter-turn and are visualized as the 'L' shape found in the corners of a square, a book, or a room. In geometry diagrams, a right angle is uniquely marked with a small square at the vertex instead of a curved arc.

Obtuse Angles measure more than $90^{\circ}$ but less than $180^{\circ}$. Visually, these angles look 'blunt' or wide, like the shape of a reclining beach chair or the hands of a clock showing 4:00.

Straight Angles measure exactly $180^{\circ}$. A straight angle forms a perfectly flat line. Visually, it looks like a single straight line with a vertex point in the middle, representing a half-turn of a circle.

Reflex Angles are angles that measure more than $180^{\circ}$ but less than $360^{\circ}$. Visually, they represent the 'outside' bend of an angle, similar to the angle formed on the back of your elbow when you bend your arm.

Full Rotation or Angles at a Point measure exactly $360^{\circ}$. This represents a complete circle. Visually, if you start at one line and turn all the way back to the start, you have completed a $360^{\circ}$ turn.

Adjacent angles on a straight line always add up to $180^{\circ}$. Visually, if you split a straight line into two or more parts with lines coming out of a single point, the sum of those 'inner' angles will always equal the straight angle ($180^{\circ}$).