Shapes and Angles - Angles in Shapes and Names

An angle is formed when two rays or line segments meet at a common endpoint called the vertex. Visually, you can think of an angle as the space or 'opening' between two fingers when you spread them apart.

A Right Angle measures exactly $90^{\circ}$. It looks like a perfect 'L' shape or the corner of a square. When you see a small square symbol in a corner, it indicates a right angle.

An Acute Angle is any angle that measures more than $0^{\circ}$ but less than $90^{\circ}$. Visually, it is 'sharper' and narrower than a right angle, similar to the tip of a pencil or a slice of pizza.

An Obtuse Angle is an angle that measures more than $90^{\circ}$ but less than $180^{\circ}$. It appears 'blunt' and wide, like the hands of a clock showing 4 o'clock or an open laptop screen tilted back.

A Straight Angle measures exactly $180^{\circ}$. It looks like a perfectly straight line. You can imagine two rays pointing in opposite directions from the same vertex to create this flat appearance.

Shapes are defined by their number of sides and angles. For example, a triangle has 3 sides and 3 angles, while a quadrilateral (like a square or rectangle) has 4 sides and 4 angles. If you change the angles of a shape without changing the side lengths, the name of the shape can change (e.g., a square becoming a rhombus).

Angles are measured in degrees using a tool called a protractor. A protractor is a semi-circular device with markings from $0^{\circ}$ to $180^{\circ}$. To measure an angle, place the center point of the protractor on the vertex and align the zero line with one side of the angle.