Chapter 5 Measurement of Length and Speed
Traditional Methods of Measurement:
- Arm length, arm length, steps: Different parts of the body, such as arm length, arm length, or number of steps, were traditionally used to measure length.
- For example, farmers measured the fields by steps.
- People like Hardeep have seen measurements being done using weapons in their family.
- Deepa and her friends measured the length of a table according to the length of the hands. They found that everyone’s arm length was different, which led to different results.
Standard Units
- Historically, people in India used units such as the finger, sagittarius, and plank for measurement.
- However, to avoid confusion, a standardized system known as the International Entity System (SI Unit) was introduced.
- The standard SI unit of length is metre (m).
- For shorter lengths, units such as centimetres (cm) and millimetres (mm) are used:
1 Meter = 100 cm
1 cm = 10 mm
- For greater distances kilometres (km) are used:
1 km = 1000 m
Measurement Instruments
- To measure a short length, it is usually 15 cm. The scale is used.
- Flexible measuring tapes are used to measure curves or large dimensions.
- An object such as thread can be used to measure curved surfaces, such as lights around a home. The thread can then be straightened and measured with a measuring scale.
The right ways to measure
- It is important to correctly place the scale with the object being measured for an accurate result.
- The position of the eye should be just above the point to be measured to avoid parallax errors.
- Even if the ends of the scale are broken, measurements can be taken by reading the scale from any whole mark (e.g., from 1 cm).
Measuring curved lines
- To measure curved lines (such as wire or decoration), a thread is used to trace the curve, and then straightened to measure it with a scale.
Description of the situation
- Reference points are used to state the position of an object relative to a certain point. For example, the position of friends’ houses or the distance from the bus stand can be indicated using a reference point.
- Dipa and her friends used a measuring lace and fixed a reference point to draw lines on the kabaddi court for the game day.
Reference points and distances
- In one instance, Padma was travelling by bus to visit her grandparents. As she passed by kilometers of stones, each one of which showed the decreasing distance of Delhi, it showed that she was getting closer to her destination.
- Reference point: In this case, Delhi became the reference point for measuring the distance from its location to its destination. Each kilometer of stone was showing its changing position relative to the reference point.
Speed and relaxation
- Momentum is defined as the change in position relative to the reference point.
- Activity 5.2: Students were asked to observe their surroundings and note which objects are stationary and which are moving.
- The position of moving objects (such as a grazing cow) varies relative to a fixed reference point.
- Stationary objects (such as trees) remain stationary, i.e., they do not change with respect to the reference point.
Types of Motion:
- Linear motion
- Circular motion
- oscillatory motion
Linear motion : When an object moves in a straight line. For example, when you drop a rubber, it falls straight down. Pushing a ball rolling in a box or a straight line are also examples of linear motion.
Circular motion: When an object moves on a circular path. For example, tying a rubber to a thread and twisting it in a circular manner imitates circular motion. Merry-go-rounds are common examples of circular motion.
Oscillatory motion: When an object rotates back and forth at a fixed point, such as a swing or pendulum spinning back and forth.
Periodic motion
If an object repeats its motion after a certain interval of time, it is said to be a periodic motion. Both circular and oscillatory motions can be periodic if they are repeated continuously.