Master Chapter 8 Class 7 - Measurement of Time and Motion (Curiosity) with comprehensive NCERT Solutions, Practice Questions, MCQs, Sample Papers, Case Based Questions, and Video lessons.
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Welcome to Chapter 8. Our journey begins as we watch television with Prerna, a student who loves to run. She’s the fastest runner in her school, and as she watches a replay of an Olympic sprint, she is amazed. She sees runners crossing the finish line so close together that they look like a single blur. Yet, the timer on the screen can tell them apart, measuring the race down to a thousandth of a second.
Prerna thinks about her own races at school, where her teacher uses a handheld stopwatch. Then she thinks about all the other ways we tell time: the watch on her mother's wrist, the clock on her school wall, the time on her sister's mobile phone, and even her uncle's talking watch . We are surrounded by devices that measure time.
This sparks a deep question in her mind: We are so good at measuring time now, but what about in the ancient past? How did people measure time when there were no clocks, no batteries, and no phones?.
This chapter is an investigation into that very question. It is a journey into one of the most fundamental concepts of our universe: Time. We will explore how humanity learned to measure it, and then, how we used that knowledge to measure something just as important: Motion.
Long before any of us were born, our ancestors were also obsessed with time. They started by noticing that many events in nature repeat themselves in definite, predictable intervals.
The Sun rises and sets, giving us the day.
The Moon changes its shape in a perfect cycle, giving us the month.
The seasons change in a reliable pattern, giving us the year.
These natural cycles were great for making calendars, but they were not very helpful for measuring smaller parts of a day. This challenge sparked human ingenuity, leading to the invention of the first "clocks". We will explore these amazing ancient devices:
Sundials: These devices used the changing position of a shadow cast by the Sun to mark the passage of the day. We will learn about the world's largest stone sundial, the Samrat Yantra at Jantar Mantar, which is so precise it can measure time down to two-second intervals! .
Water Clocks: These devices used the steady flow of water to measure time. We will learn about the Ghatika-yantra from ancient India, a clever "sinking bowl" clock that was used to announce the time to entire towns .
Sand Clocks (Hourglasses): These used the flow of sand from one bulb to another.
Candle Clocks: These were candles with markings that showed how much time had passed as they burned down.
We will even build our own simple water clock using a plastic bottle, just to see how these ancient principles work .
For centuries, these clocks were good, but they were not perfect. Water flow could change, and sundials did not work at night. The world needed a truly reliable, constant, and predictable way to measure time.
The breakthrough came from a simple observation. The chapter tells the story of the great scientist Galileo Galilei. While sitting in a church, he watched a lamp suspended from the ceiling swinging back and forth. Using his own pulse as a timer, he made a revolutionary discovery: no matter how wide or narrow the swing, the lamp always took the same amount of time to complete one full swing .
This is the principle of the pendulum. It is an oscillatory motion—a motion that repeats itself over a fixed interval of time .
We will investigate this ourselves by building our own simple pendulum (a bob hanging from a string). We will measure its time period—the exact time it takes for one complete oscillation. And like Galileo, we will discover its secret: the time period of a pendulum is incredibly constant.
This single discovery changed the world. It led to the invention of the first modern pendulum clocks and is the basic principle behind all timekeeping today, from quartz watches to ultra-precise atomic clocks .
Now that we have a way to reliably measure time in a standard unit—the second (s) —we can finally return to Prerna's world of sports.
Knowing the time of a race is one thing. But how can we compare runners in different races? How do we answer the question, "Who is faster?"
To do this, we need a new concept that combines time with distance. That concept is Speed.
What is Speed? We will define speed as the distance an object covers in a unit of time (for example, how many metres it covers in one second).
The Formula: We will learn the fundamental formula that scientists and engineers use every day:
Speed = Total distance covered / Total time taken
The Units: We will learn the standard units for speed, like metres per second (m/s) and kilometres per hour (km/h) .
This chapter is a big leap. We are connecting an ancient human quest—the desire to measure time—with the fundamental physics of how things move. You will learn new terms like 'oscillation' and 'time period' and, for the first time, use a core scientific formula: Speed = Distance / Time. It can be a challenge to link Galileo's swinging lamp to a math problem about a train .
This is exactly where Teachoo becomes your best training partner. We excel at breaking down these big concepts. We will walk you through the pendulum experiment step-by-step, and then show you exactly how to use the speed formula with clear, simple examples. We help you build the confidence to not just learn the formula, but to use it like a scientist to measure the world.
Finally, once we know how to calculate speed, we can begin to describe it.
Think about a train traveling between two stations. Does it move at the same speed the entire time? Of course not. It starts slowly, speeds up, cruises, and then slows down again to stop.
This leads us to our final, important classification of motion:
Non-uniform Motion: This is when the speed of an object moving in a straight line keeps changing (like the train starting and stopping) . This is what we experience most of the time in our daily lives.
Uniform Motion: This is when an object moves along a straight line at a constant, unchanging speed (like the train cruising for a while between stations) . An object in uniform motion covers equal distances in equal intervals of time.
This is also why we almost always talk about average speed. When we say a car's speed was 60 km/h for a trip, we don't mean it was always 60. We mean that was its average speed over the total distance and total time of the journey .
This chapter will take you on a journey from ancient sundials to modern physics. You will learn not just how to tell time, but how to measure it, and how to use it to unlock the secrets of motion.
To get started on this exciting journey, click on any topic link to begin your exploration.