Measurement of | Class 7 Science Notes

Speed

Speed is a measure of how fast an object is moving. When comparing the motion of different objects, speed helps us determine which object is moving faster or slower.

Speed is defined as the distance covered by an object in a unit time. The unit time can be one second, one minute, or one hour, depending on the context.

Mathematically, speed is calculated as:

Speed = Total distance covered ÷ Total time taken

The SI unit of speed is metre per second (m/s), as distance is measured in metres and time in seconds. However, speed can also be expressed in other units such as kilometres per hour (km/h), where distance is in kilometres and time in hours.

To convert speed from km/h to m/s, multiply by (1000 m / 1 km) and divide by (3600 s / 1 h), which simplifies to multiplying by 5/18.

An example illustrates this: Swati's school is 3.6 km from her house, and it takes her 15 minutes to reach school by bicycle. To find her speed in m/s, convert 3.6 km to 3600 m and 15 minutes to 900 seconds. Then,

Speed = 3600 m ÷ 900 s = 4 m/s.

Students are encouraged to look up train timetables, note distances and times between stations, and calculate speeds of various trains, comparing passenger, express, and superfast trains.

Speed is a fundamental concept in understanding motion and is essential for describing how quickly objects move in everyday life and scientific contexts.

📊 Diagram: Fig. 8.10 shows boys running a race on a straight track, illustrating that the runner ahead at a given time is moving faster.

🧪 Activity: Activity 8.4 involves students using railway timetables to find distances and times between stations, calculating the speeds of different trains, and comparing which train is fastest.

🔗 Connection: This section introduces speed, leading to the relationship between speed, distance, and time in the next section.