Measurement & Data
Ordering Objects by Length
Comparing and ordering up to three objects by length.
Longer, Shorter, or the Same?
Before measuring how long something is with a number, it helps to first compare lengths directly — deciding which of a few objects is longest, which is shortest, and which are the same length.
Definition — Length
To compare two objects fairly, line up one end of each object together, then look at where the other ends land. The object whose far end reaches further is longer. To order three or more objects, compare them two at a time.
Worked Example — Ordering Three Pencils
Worked Example — Using a Middle Object to Compare
Tip
Common Mistakes
Comparing two objects without lining up their starting ends, leading to a wrong conclusion about which is longer.
Always align one end of both objects first — like lining up the bottoms of two pencils — before comparing where the other ends land.
Judging length by an object's overall size or width instead of by how far it stretches from end to end.
Length only depends on the distance from one end to the other, not how wide, thick, or heavy the object is.
Key Takeaways
- Length is the distance from one end of an object to the other.
- Line up one end of two objects evenly before comparing their lengths.
- Objects can be ordered by comparing them two at a time, even using a middle object to compare two that aren't lined up directly.
Summary
Ordering objects by length compares them directly, without using numbers yet. The next lesson takes that same idea further by measuring length with a number, using a simple repeated unit.
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