NCERT Class 7 Science Chapter 8
Measurement of Time and Motion
This chapter introduces CBSE Class 7 students to the concepts of time, speed, and different types of motion. Students learn to measure time using various instruments, calculate speed using the formula speed = distance/time, and differentiate between uniform and non-uniform motion. The chapter also explores how motion is described using distance-time graphs.
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Key Terms
- Motion
- The change in the position of an object with respect to its surroundings over a period of time.
- Speed
- The distance covered by an object per unit of time, calculated using the formula: Speed = Distance ÷ Time. The SI unit of speed is metres per second (m/s).
- Uniform Motion
- Motion in which an object covers equal distances in equal intervals of time, maintaining constant speed throughout.
- Non-uniform Motion
- Motion in which an object covers unequal distances in equal intervals of time, meaning its speed changes over time.
- Distance-Time Graph
- A graphical representation of an object's motion where distance is plotted on the Y-axis and time on the X-axis. A straight line indicates uniform motion.
- Oscillation
- A repetitive back-and-forth or to-and-fro motion, such as the swinging of a pendulum. The time for one complete oscillation is called its time period.
Frequently Asked Questions
What is the formula for speed in Class 7 Science?▾
Speed is calculated using the formula: Speed = Distance ÷ Time. If distance is in metres and time is in seconds, speed is in metres per second (m/s). If distance is in kilometres and time is in hours, speed is in kilometres per hour (km/h).
What is the difference between uniform and non-uniform motion?▾
In uniform motion, an object covers the same distance in every equal interval of time (constant speed), like a car on a highway at steady speed. In non-uniform motion, the distances covered in equal time intervals are different, like a car in city traffic.
How do you read a distance-time graph?▾
In a distance-time graph, the X-axis shows time and the Y-axis shows distance. A straight line with a slope indicates uniform motion — the steeper the line, the faster the speed. A curved line indicates non-uniform motion, and a horizontal line means the object is at rest.
What is a simple pendulum and how is it used to measure time?▾
A simple pendulum consists of a string with a bob (small weight) attached. It swings back and forth in a regular pattern. The time for one complete swing (time period) remains constant for a given length, making it useful for measuring time accurately.
What are the SI units of distance, time, and speed?▾
The SI unit of distance is the metre (m), the SI unit of time is the second (s), and the SI unit of speed is metres per second (m/s). For longer distances, kilometres (km) and hours (h) are commonly used.
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