Measurement (length)
Measure of length
What is Length?
Length tells us how long something is. We measure the length of objects to know their size, like how long a pencil is or how tall a building is.
Units of Length
There are different units to measure length. For Class 3, we focus on two main systems of measurement:
1. Standard Units (Metric System):
These are units we use all around the world.
– Millimeter (mm): The smallest unit of length. Very tiny things, like the thickness of a paper, are measured in millimeters.
– Centimeter (cm): There are 10 millimeters in 1 centimeter. We use centimeters to measure things like the length of a pencil or a book.
– Meter (m): There are 100 centimeters in 1 meter. We measure larger objects like the length of a room or a playground in meters.
– Kilometer (km): There are 1000 meters in 1 kilometer. We use kilometers to measure long distances, like the distance between two cities.
2. Non-Standard Units:
Before learning about the metric system, students might have measured length using their hand spans, foot lengths, or even using objects like paperclips or pencils. These are called non-standard units because they vary from person to person.
Tools to Measure Length
– Ruler: Measures in centimeters and millimeters. Good for small objects like books or notebooks.
– Measuring Tape: Used to measure larger things like the length of a table or a room. It shows measurements in both centimeters and meters.
Converting Between Units
Understanding how to switch between different units is important:
– 1 meter = 100 centimeters
– 1 centimeter = 10 millimeters
– 1 kilometer = 1000 meters
Examples:
1. A pencil is 15 cm long.
2. A classroom is 7 meters wide.
3. The distance between two towns is 10 kilometers.
Conversion of meters into centimeters and vice-versa
Understanding Meters and Centimeters:
– Meter (m) is a standard unit of length. It is used to measure longer things like the height of a door or the length of a room.
– Centimeter (cm) is a smaller unit of length. There are 100 centimeters in 1 meter.
Converting Meters into Centimeters:
To convert meters into centimeters, we multiply by 100. This is because 1 meter = 100 centimeters.
Example 1:
Convert 5 meters into centimeters.
– Since 1 meter = 100 centimeters, we multiply:
5 x 100 = 500 cm
– So, 5 meters = 500 centimeters.
Example 2:
Convert 2.5 meters into centimeters.
– Multiply 2.5 by 100:
2.5 x 100 = 250 cm
– So, 2.5 meters = 250 centimeters.
Converting Centimeters into Meters:
To convert centimeters into meters, we divide by 100. This is because 100 centimeters = 1 meter.
Example 1:
Convert 300 centimeters into meters.
– Since 100 centimeters = 1 meter, we divide:
300 ÷ 100 = 3 m
– So, 300 centimeters = 3 meters.
Example 2:
Convert 250 centimeters into meters.
– Divide 250 by 100:
250 ÷ 100 = 2.5 m
– So, 250 centimeters = 2.5 meters.
Summary:
– To convert meters to centimeters: Multiply the number of meters by 100.
– To convert centimeters to meters: Divide the number of centimeters by 100.
Conversion of Kilometers into meters
Understanding Kilometers and Meters:
– Kilometer (km) is a larger unit of length. It is used to measure long distances, like the distance between two cities or towns.
– Meter (m) is a smaller unit of length. We use meters to measure shorter distances, like the length of a room or the height of a tree.
Important fact:
1 kilometer = 1000 meters
Converting Kilometers into Meters:
To convert kilometers into meters, we multiply by 1000. This is because 1 kilometer = 1000 meters.
Example 1:
Convert 3 kilometers into meters.
– Since 1 kilometer = 1000 meters, we multiply:
3 x 1000 = 3000 m
– So, 3 kilometers = 3000 meters.
Example 2:
Convert 5.5 kilometers into meters.
– Multiply 5.5 by 1000:
5.5 x 1000 = 5500 m
– So, 5.5 kilometers = 5500 meters.
Summary:
– To convert kilometers to meters: Multiply the number of kilometers by 1000.
Kilometers x 1000 = Meters
Word problem
Word Problem 1: Measuring Length
John has a rope that is 5 meters long. He cuts 2 pieces from the rope, each measuring 120 centimeters. How much rope is left?
Solution:
1. Convert 120 cm to meters:
120 cm = 1.2 m
2. Total length of 2 pieces:
1.2 x 2 = 2.4 m
3. Subtract the total length of the pieces from the original rope:
5 – 2.4 = 2.6 m
Answer: John has 2.6 meters of rope left.
Word Problem 2: Conversion between Kilometers and Meters
A school is organizing a race. The total race is 3 kilometers long. After running 1200 meters, how much more distance do the students need to run?
Solution:
1. Convert the total race distance to meters:
3 km = 3000 m
2. Subtract the distance already run:
3000 – 1200 = 1800 m
Answer: The students need to run 1800 more meters.
Word Problem 3: Measuring Height
A tree is 8 meters tall. A nearby bush is 150 centimeters tall. What is the difference in height between the tree and the bush?
Solution:
1. Convert the height of the bush to meters:
150 cm = 1.5 m
2. Subtract the height of the bush from the height of the tree:
8 – 1.5 = 6.5 m
Answer: The difference in height is 6.5 meters.