Comparing and Measuring Length for Primary 1

Length

Performance Objectives

By the end of the lesson, students should be able to:

1. develop the idea of length;
2. compare length of two or three objects;
3. order similar objects according to length using symbols e.g. ;
4. measure length and distance in their units
5. apply the length and ordering of lengths in our environment

What is Length?

Length tells us how long something is from one end to the other.

When you want to know how long a pencil is, or how tall a person is, you are thinking about length. Length helps us describe the size of objects.

Some objects are long, and some are short. Some are tall, and some are not tall.

Comparing Lengths of Objects

We often compare objects to see which one is longer or shorter. To compare lengths, objects can be placed side-by-side.

Comparing Two Objects

When comparing two objects, one can be longer than the other, or shorter than the other. Sometimes, two objects can have the same length.

For example, a school ruler is usually longer than a pencil. A small book is shorter than a big book.

When comparing the height of people or objects that stand upright, we use the words ‘tall’ and ‘short’. A tall person is someone with a great height, while a short person has a small height. A tall tree is higher than a short bush.

Comparing Three Objects

When comparing three objects, we can find the longest object, the shortest object, or objects that are of similar length.

Imagine three different sticks. One stick might be very long, another might be medium, and the third might be very short. By placing them next to each other, it is easy to see which is the longest and which is the shortest.

Ordering Lengths of Objects

Ordering lengths means arranging objects from the shortest to the longest, or from the longest to the shortest.

Arranging from Shortest to Longest

To arrange objects from shortest to longest, first find the shortest object. Then find the next shortest, and so on, until the longest object is placed last.

Arranging from Longest to Shortest

To arrange objects from longest to shortest, first find the longest object. Then find the next longest, and so on, until the shortest object is placed last.

Using Symbols to Order Lengths

We can use special symbols to show how lengths compare:

1. The symbol $<$ means "is shorter than" or "is less than".
2. The symbol $>$ means “is longer than” or “is greater than”.

For example, if a red stick is shorter than a blue stick, we can write:

$$ \text{Red stick} < \text{Blue stick} $$

If a green rope is longer than a yellow rope, we can write:

$$ \text{Green rope} > \text{Yellow rope} $$

When ordering three objects, such as Stick A, Stick B, and Stick C, where Stick A is the shortest, Stick B is medium, and Stick C is the longest, we can write:

$$ \text{Stick A} < \text{Stick B} < \text{Stick C} $$

This means Stick A is shorter than Stick B, and Stick B is shorter than Stick C.

<!– SUREPASS_VISUAL
type: ai
format: image
use_case: educational_diagram
description: An illustration showing three pencils of different lengths arranged in order from shortest to longest. Below them, text labels indicate their names (e.g., Pencil A, Pencil B, Pencil C) and the comparison using symbols: Pencil A < Pencil B < Pencil C.
alt: Three pencils arranged from shortest to longest, labelled Pencil A, Pencil B, Pencil C. Below them, the text "Pencil A < Pencil B

Measuring Length

Measuring length means finding out exactly how long something is. For Primary 1, we can measure length using non-standard units. Non-standard units are things like your hand span, footsteps, or a stick.

Measuring with Non-Standard Units

Non-standard units are useful for understanding the idea of measurement before using standard tools like rulers.

1. Hand Span: The distance from the tip of your thumb to the tip of your little finger when your hand is stretched out.
2. Footstep: The length of one step you take.
3. Stick or String: A piece of stick or string can be used to mark and compare lengths.

How to Measure the Length of an Object

The procedure involves the following steps:

1. Choose an object to measure, for example, a table.
2. Choose a non-standard unit, such as your hand span.
3. Place your hand at one end of the table.
4. Mark where your hand span ends.
5. Move your hand and place the start of your hand span at the mark you just made.
6. Count how many hand spans it takes to cover the entire length of the table.
7. The number of hand spans is the length of the table in hand spans.

For example, a table might be 5 hand spans long, or a classroom might be 10 footsteps long.

Measuring Tools

Tools like rulers and measuring tapes are used to measure length more accurately. These tools have markings that help us find the exact length of objects. For Primary 1, it is important to know that these tools exist and are used for measuring, even if we are still learning to use non-standard units.

Applying Length and Ordering in Our Environment

The idea of length and ordering lengths is used in many ways in our daily lives:

1. Comparing Heights: Children compare their heights to see who is taller or shorter.
2. Arranging Objects: Books on a shelf can be arranged from the shortest to the tallest.
3. Building and Construction: Builders measure the length of wood or bricks needed for a house.
4. Playing Games: In races, we measure distances to see who runs the longest or shortest distance.
5. Making Clothes: Tailors measure the length of fabric to make clothes that fit well.

In school, children often line up for assembly or to go to the playground. Sometimes, they are asked to line up from the shortest to the tallest. This is an example of ordering by length (height) in our environment.