Class 7 Science Chapter 9 Question Answers - Time and Motion

Short Types Questions

Measuring time has been important in human history for various reasons such as predicting seasonal changes, determining the duration of events, and measuring work hours.

Q.2. Name some instruments used to measure time.

Some instruments used to measure time are sundials, water clocks, hourglasses, mechanical clocks, and digital clocks.

Q.3. Who was Christiaan Huygens, and what was his contribution to the measurement of time?

Christiaan Huygens was a Dutch mathematician, physicist, and astronomer who invented the pendulum clock in 1656, which revolutionized the measurement of time.

Q.4. What is the difference between speed and average speed?

Speed refers to how fast an object is moving, while average speed is the total distance traveled divided by the time taken to travel that distance.

Q.5. How can distance and time graphs be used to analyze motion?

Distance and time graphs show how an object's position changes over time. By analyzing the slope of the graph, we can determine the object's speed, and by looking at the shape of the graph, we can determine whether the object is moving at a constant speed or accelerating.

Long Types Questions

Measuring time has been vital for human history as it has helped in organizing daily activities, such as work, travel, and communication. It has helped in the development of calendars, time zones, and the standardization of time. Time keeping has also been crucial in scientific discoveries, such as the study of planetary motion and the measurement of speed. Overall, measuring time has contributed to the progress and development of human society.

Q.2. What were some of the instruments used to measure time in ancient civilizations? How were they different from modern-day timekeeping devices?

Ancient civilizations used various methods to measure time, such as sundials, water clocks, and hourglasses. These devices relied on natural phenomena such as the sun, water flow, and sand to measure time. Modern-day timekeeping devices, such as clocks and watches, use more precise methods, such as quartz crystal oscillation and atomic clocks. Thus, modern devices are more accurate and reliable compared to ancient timekeeping instruments.

Q.3. Explain the concept of periodic motion. How is it used to measure time?

Periodic motion refers to any motion that repeats at regular intervals. The simple pendulum is an example of periodic motion, where the pendulum swings back and forth in a regular motion. By measuring the time it takes for the pendulum to complete one full swing, we can calculate the time accurately. Periodic motion is used in modern-day clocks, where the oscillation of a quartz crystal is used to measure time accurately.

Q.4. What is the difference between speed and average speed? How are they calculated?

Speed is the rate of change of distance with respect to time, while average speed is the total distance traveled divided by the total time taken. Speed is calculated by dividing the distance traveled by the time taken, while average speed is calculated by dividing the total distance by the total time. For example, if a car travels 100 km in 2 hours, its speed is 50 km/h, while its average speed is also 50 km/h if it travels the same distance in the same time.

Q.5. Why is it important to measure speed and drive safely? How can distance and time graphs help analyze motion?

Measuring speed is crucial for safe driving as it helps in maintaining the appropriate speed limit and avoiding accidents. Distance and time graphs help in analyzing the motion of an object by plotting the distance traveled on the y-axis and the time taken on the x-axis. The slope of the graph represents the speed of the object, and any changes in the slope indicate changes in speed or motion. By analyzing the graph, we can determine the speed of the object, the time taken, and the distance traveled, which can help in making informed decisions while driving.