Shape and Space: Measurement, 2-D and 3-D Figures, and Position
What you must understand
Shape and space in Grade 3 covers naming and describing 2-D shapes (triangles, quadrilaterals including squares, rectangles, and parallelograms) by their sides and corners, and 3-D objects (cubes, prisms, pyramids, cylinders, cones, spheres) by faces, edges, and vertices. You must measure length in centimetres and metres, find perimeter by adding side lengths, and understand area as the number of square units covering a surface. Symmetry, congruence, and positional language (left, right, above, below, between) also appear.
Traps to watch for
- Perimeter versus area: perimeter is a distance around the edge (in cm); area is a count of squares (in square cm). Mixing units is a common error.
- Shape classification: a square is a rectangle, but a rectangle is not always a square; a rhombus has four equal sides but need not have right angles.
- Counting faces and edges: a cube has 6 faces, 12 edges, and 8 vertices; students frequently count edges as 6.
- Measuring from the end: place the object at the 0 mark, not at the ruler's edge.
- Symmetry: a shape may have more than one line of symmetry, and a diagonal is not always one.
Worked example
A rectangle is 6 cm long and 4 cm wide. Perimeter = 6 + 4 + 6 + 4 = 20 cm. Area = 6 × 4 = 24 square centimetres. Note the different units: the perimeter answer is a length, the area answer is in square units.
Rule of thumb
Ask yourself whether the question is about the distance around (add the sides) or the space inside (multiply length by width). Label every answer with its unit.