Time and Motion PDF

# Time and Motion ## How do speed and time play an important role in our life? **Trigger Time** Why do we need to measure time? In our daily life, we make measurements most of the time. For example, we buy vegetables by weighing them, we measure our body temperature when we are ill, we go to...

# Time and Motion ## How do speed and time play an important role in our life? **Trigger Time** Why do we need to measure time? In our daily life, we make measurements most of the time. For example, we buy vegetables by weighing them, we measure our body temperature when we are ill, we go to school at a fixed time. How do we get to know the time? We know the time with the help of clocks and watches. ## Measurement of Time in Ancient Times In ancient times, people did not have clocks or watches for knowing time. But those people knew the importance of time. Our ancestors used some natural events that repeat regularly after definite intervals of time, to measure time. For example, - The time taken between one sunrise to the next sunrise was called a 'day' or 'solar day'. - The time taken between one new moon to the next new moon was called a 'month'. - The time taken by the earth to complete one revolution of the sun was called an 'year'. ## Activity 1 *Experiential Learning (NEP Guidelines)* Recall and identify the types of motion in the given examples. | Examples of motion | Type of motion (Straight line, circular, periodic) | |---|---| | Earth spinning on its axis | Circular | | Pendulum of a clock | Periodic | | A swing in motion | Periodic | | A moving car on a road on hills | Circular | | A bird flapping its wings | Periodic | | An ant trail moving in search of food | Straight line | ELO: Recall how time was measured in ancient times. ## Do We Know? (Science in Life) *NEP Guidelines* The Maharaja of Jaipur, Sawai Jai Singh II, built the biggest sundial in the world called 'Samrat Yantra' in the year 1728. The sundial is a part of the observatory called Jantar Mantar built at Jaipur. It is the largest and an extremely accurate sun clock that determines the local time. The other Jantar Mantar observatories are located at Delhi, Varanasi and Ujjain. Research on the Internet about the special features of these observatories. ## Simple Pendulum A simple pendulum consists of a small metal ball (called bob) suspended by a long thread from a rigid support, such that the bob is free to swing back and forth. The motion of pendulum was first studied by Galileo. A simple pendulum is shown in the Figure 9.3(a). ### Some Terms Related to Simple Pendulum: 1. **Length of the pendulum:** The length of the string (thread) from the point of suspension to the centre of the bob is called the length of the pendulum. In Figure 9.3(b), 'l' is the length of the pendulum. 2. **Mean position of the bob:** The position of the bob when it is at rest is called its mean position. In Figure 9.3(b), the position A is the mean position of the bob. 3. **Extreme positions of the bob:** The positions where the bob is at the maximum distance from the mean position are called the extreme positions. In Figure 9.3(b), the positions B and C are the extreme positions of the bob. 4. **Oscillation of the pendulum:** One complete to-and-fro motion of the bob about its mean position is called an oscillation of the pendulum. For example, the motion of the bob from A to B, then from B to C and back to A is called one oscillation. 5. **Amplitude of the pendulum:** As the pendulum oscillates to-and-fro, the maximum displacement of the bob from its mean position on either side is called the amplitude of the pendulum. Thus, the displacement AB or AC is called amplitude of the pendulum. 6. **Time period of the pendulum:** The time taken by the bob of a pendulum to complete one oscillation is called the time period of the pendulum. In Figure 9.3(b), the time taken by the bob of the pendulum to travel from A to B and then B to C and finally back to A is called the time period of the simple pendulum. 7. **Frequency of the pendulum:** The number of oscillations made by a pendulum in 1 second is called its frequency. **Frequency (f) = 1 / Time period (T)** ## Activity 2 *Experiential Learning (NEP Guidelines)* To determine the time period of a pendulum - Set up a simple pendulum as shown in Figure 9.4 with the thread carrying the bob at its lower end and tied at its upper end from a rigid support (like an iron stand). - Switch off the nearby fans. - Let the bob of the pendulum come to rest at its mean position. Mark the position of the bob on the floor below it (A). - To set the pendulum in motion, hold the bob gently and move it slightly to one side, say at B. Now, gently release the bob from its displaced position B. (Do not push the bob while releasing it.) Ensure that the bob does not spin on its axis while oscillating. - Start the stopwatch when the bob is at one of the extreme positions. Keep on counting the number of oscillations made by the pendulum bob. - Measure the time that the pendulum bob takes to make 20 complete oscillations. Repeat the same activity by pulling the bob to a greater or a lesser distance from the mean position, by changing bob and then, by changing the length of the pendulum. **Question Time** 1. How does the length of the pendulum affect the time period of a pendulum? 2. How does the change in material of the bob affect the time period? 3. If the mass of the pendulum is doubled, will it change its time period? ## Do We Know? (Science in Life) *NEP Guidelines* Italian scientist Galileo Galilei was the first one to make use of the pendulum. Once Galileo was sitting in a Cathedral (church) in Pisa (Italy). There, he saw a chandelier hanging from the ceiling with a long chain swinging slowly. So, Galileo timed the oscillations by counting the beats of his pulse. On careful observation, he found that while the oscillations of the chandelier gradually slowed down, the time taken by one oscillation still remained the same. In other words, a pendulum of a given length always takes the same time to complete one oscillation. This observation led to the development of pendulum clocks. **Numerical:** A simple pendulum takes 32 seconds to complete 20 oscillations. What is the time period of this pendulum? **Solution:** Time taken for 20 oscillations = 32 s So, time taken for 1 oscillation = 32 / 20 = 1.6 s Thus, the time period of this pendulum is 1.6 seconds. ELO: Explore the latest trends in the measurement of time and recall the different units of measurement for time. ## Look Beyond: (Inquiry Driven) *NEP Guidelines* Research and find out the evolution in the types of devices used to measure time. Write a journal on it and share in class. ## Latest Trend in Measurement of Time The principle of simple pendulum is used in pendulum clocks. The oscillations of the pendulum control the movement of the hands of the clock. A mechanical wristwatch does not have a pendulum. Instead, it has a balance wheel that controls the movements of its hands. These days, most of us use quartz clocks and watches. Quartz has a unique property of oscillating when subjected to a small amount of electric current. In these watches, an electric cell and a quartz crystal are placed in an electric circuit. The quartz clocks are more accurate than pendulum clocks. For measuring short intervals of time, a stop-watch is used. It is started or stopped with the help of a push-button and is used to measure short intervals of time. For example, at sports events it can measure one-tenth of a second. Nowadays, digital stopwatches are also available in the market. These digital watches display time in digits. For the most accurate measurement, atomic clocks are used. These clocks are based on vibrations of atoms for measuring time. A timer is a special type of clock used to record the sequence of an event. It is used in microwaves, washing machines, traffic signals and air conditioners. ## Unit of Time The standard unit of measuring time is second and is written as 's'. The larger units of time are minutes and hours, written as 'min' and 'h', respectively. Some units and their conversions are as follows: - 60 seconds = 1 minute - 60 minutes = 1 hour - 24 hours = 1 day - 30 days = 1 month - 12 months = 1 year - 10 years = 1 decade - 100 years (or 10 decades) = 1 century ## Do We Know? (Science in Life) *NEP Guidelines* Jun Ye, a physicist with the joint venture of the National Institute of Standard and Technology and the University of Colorado Boulder, made instrumental developments to the invention of optical lattice clocks. He has won the 2022 Breakthrough Prize in fundamental Physics. It is accurate to lose one second in every 15 billion years. This clock allows researchers to take more accurate measurements of black holes. It also helps to find the lava underneath rock, water under the desert or depth of the ocean. - All the clocks and watches use the principle of periodic motion for measuring time. - Sundial, sand clock and water clock are some important time measuring devices used in ancient times. - A simple pendulum consists of a small metal ball suspended by a long thread. ## Slow and Fast Motion When you go to school by a bicycle, it takes a long time. But when you go by a school bus, it takes lesser time. You say that a bus moves fast, whereas a bicycle moves slow. An object which takes a longer time to cover a certain distance is said to be slow, whereas an object which takes a shorter time to cover the same distance is said to be fast. ### Digital Learning *NEP Guidelines* - Which is the fastest bird on earth that flies at a speed of 300 km/hour? - Which is the fastest land animal on earth that runs at a speed of 112 km/hour? Even the same object may move fast at one point of time and slow at some other time. A bus may move slowly on a busy road and faster on an empty road. You can find out whether an object is slow or fast by knowing its speed. ELO: Define and calculate the speed of a moving object. ## Speed **Trigger Time** By calculating speed, can we also find the direction of the moving object? The most convenient way to find which of the two or more objects is moving faster, is to compare the distances travelled by them in a unit time. Speed of a moving object is the distance travelled by it in a unit time. When you know the distance travelled by an object and the time taken by it to cover that particular distance, you can calculate the speed of that object by using the formula: **Speed = Distance travelled / Time taken** Suppose, a car travels a distance of 240 km in 4 hours, then its speed will be: Speed = 240 Km / 4 h = 60 km/h Thus, the speed of this car is 60 kilometres per hour. ## Do I know my car? *NEP Guidelines* Explore your car and look around for the devices located on the dashboard that help you to find the speed and the distance travelled. ## Units of Speed The standard unit of distance is metre (m) and that of time is second (s). So, the standard unit of speed is metre per second (m/s). The speed of fast moving objects like cars, trains and aeroplanes is usually expressed in the unit of kilometres per hour (km/h). ## Speedometer and Odometer When you look at the dashboard of the car, you find many instruments on it. A speedometer is an instrument on a vehicle's dashboard that indicates the speed of the vehicle at that interval of time in kilometres per hour (km/h). Odometer is an instrument which shows the distance travelled by the vehicle in kilometres - **An object is said to be in motion when its position changes with time or with respect to its surroundings.** - **Speed of a moving object is the distance travelled by it in a unit time.** - **Speedometer is an instrument which indicates the speed of a vehicle. Odometer is an instrument which shows the distance travelled by a vehicle in kilometres.** ## Multiple Choice Questions *Understanding, Applying* 1. Which of these instruments is likely to help in measuring the speed of an object? - Anemometer - Beaker - Thermometer - Watch 2. A student observes the positions of two vehicles at different instants of time as shown. Which of these statements explains the motion of the vehicles? - Car A is in motion as it changed its position with respect to the surroundings. - Car B is in motion as it changed its position with respect to the surroundings. - Car A is in motion as it did not change its position with respect to the surroundings. - Car B is in motion as it did not change its position with respect to the surroundings. 3. Rajat was investigating the factors affecting the time period of a simple pendulum. He doubled the length of the string of the simple pendulum and calculated the time period. How will it change the time period of the simple pendulum? - Time period will be change to twice - Time period reduces to half - Does not change - Reduces to 1/4th ## Numerical Problems Based on Speed **Numerical 1:** The speed of a moving car is 72 km/h. Calculate its speed in m/s. **Solution:** Here, speed of the car = 72 km/h We know, 1 km = 1000 m And, 1 h = 60 × 60 s = 3600 s So, speed (in m/s) = 72 × 1000 m / 1 × 3600 s = 20 m/s Therefore, the speed of the moving car is 20 m/s. **Numerical 2:** A school bus takes 45 minutes to cover a distance of 27 km. Calculate its speed in km/h and m/s. **Solution:** Here, distance travelled = 27 km Time taken = 45 minutes (to be converted into hours) 45 h = 3/4 h (We know 1 h = 60 minutes) We know, Speed = Distance travelled / Time taken 27 km / 3/4 h = 27 × 4 / 3 km/h = 36 km/h … Therefore, the speed of the bus is 36 km/h. **Numerical 3:** A car moves at a speed of 40 km/h for 15 minutes and then at a speed of 60 km/h for the next 15 minutes. Calculate the total distance covered by the car. **Solution:** (i) In the first case: Speed = 40 km/h Time taken = 15 minutes 15 h = 1/4 h ( We know, Speed = Distance travelled / Time taken) or, Distance travelled = Speed × Time taken Distance travelled = 40 km/h × 1/4 h= 10 km (ii) In the second case: Speed = 60 km/h Time taken = 15 minutes 15 h = 1/4 h … Distance travelled = Speed × Time taken = 60 km/h × 1/4 h = 15 km Total distance travelled = 10 km + 15 km = 25 km Thus, the total distance covered by the car is 25 km. **Trigger Time** - Situation A- Rajiv was driving on a highway at the speed of 50 km/hr. He was not applying brakes to his vehicle as the road was clear and smooth. - Situation B- Nusreen was driving in the city with irregular speed as she needed to apply brakes frequently due to heavy rush. Who among Rajiv and Nusreen was travelling with a uniform speed? **Numerical 4:** The odometer of a car reads 57321.0 km when the clock shows the time as 8.30 am. What is the distance travelled if at 8.50 am, the odometer reading has changed to 57336.0 km? Also calculate the speed of the car in km/h. **Solution:** Here, initial reading of odometer = 57321.0 km Final reading of odometer = 57336.0 km Distance travelled by the car = Initial reading - Final reading = 57336.0 km - 57321.0 km = 15 km Distance travelled by the car is 15 km Time taken = 8.50 am - 8.30 am = 20 minutes = 20/60 h = 1/3 h We know, Speed = Distance travelled / Time taken = 15 km / 1/3 h = 15 km × 3 / 1 h = 45 km/h Thus, the speed of the car is 45 km/h. ## Uniform and Non-Uniform Motion **ELO:** Describe and differentiate uniform and non uniform motion. Suppose, an object (say a car or a scooter) keeps on moving along a straight line path. When it keeps on covering equal distances in equal intervals of time, its speed remains constant. Such a motion of an object is called uniform motion. Thus, an object moving along a straight line path is said to have a uniform motion if its speed remains constant. For example, when a car is moving at a constant speed of 60 km/h, it covers equal distance of 60 km in every 1 hour, 30 km in every half hour and 15 km in every quarter hour and so on. But this may not actually be possible in day-to-day situations due to heavy traffic and bad roads. Thus, in real life situations, you hardly find objects moving at a uniform motion. An object moving along a straight line path is said to have a non-uniform motion when its speed keeps changing (i.e., it does not remain constant). An object having a non-uniform motion travels 'unequal distances' in equal intervals of time, or 'equal distances' in unequal intervals of time. For example, as a train moves out of the railway platform, it covers a distance of 1 km in 10 minutes and the next 2 km again in 10 minutes. The train then picks up speed and travels the next 10 km in 10 minutes. When you calculate the speed of the train for various distances, you realise that the train has not covered the complete distance at the same speed. So, the motion of the train is called non-uniform motion. ## Distance-Time Graph The motion of objects showing relationship between distance travelled and time taken to cover that distance is represented in a diagram formed by drawing their distance-time graphs. A distance-time graph shows how the distance travelled by a moving object changes with time. Graphs are generally plotted on a graph paper. Let us learn to make a distance-time graph (line graph) of the following data: | S.No. | Time | Distance | |---|---|---| | 1. | 0 min | 0 km | | 2. | 1 min | 1 km | | 3. | 2 min | 2 km | | 4. | 3 min | 3 km | | 5. | 4 min | 4 km | | 6. | 5 min | 5 km | 1. Draw two lines at right angle to each other on a graph paper as shown in Figure 9.9. Mark the horizontal line as OX. This is known as X-axis. Similarly, mark the vertical line as OY. This is called Y-axis. The point of intersection of OX and OY is known as the origin 'O'. 2. The quantity that is made to vary at our will is called the independent variable and the other that varies as a result of this change is called the dependent variable. In this case, time is an independent quantity, so time is shown along the X-axis. Label the X-axis by writing 'Time' and its unit 'min' in brackets followed by an arrow (→). In this case, distance is a dependent quantity, so distance is shown along the Y-axis. Label the Y-axis by writing 'Distance' and its unit 'km' in brackets followed by an arrow (→). 3. You should choose suitable scales, so as to represent the large values of 'time' and 'distance' conveniently on the small graph paper. For the motion of the car, scales in this case could be: - Time: 1 min = 1 cm (or 1 big square on X-axis) - Distance: 1 km = 1 cm (or 1 big square on Y-axis) 4. Mark values for the time and the distance on the respective axes according to the scale you have chosen. In this case, for the motion of the car, mark the time 1 min, 2 min, ... on the X-axis from the origin O. Similarly, mark the distance 1 km, 2 km, ... on the Y-axis from the origin O. 5. Observation recorded at S.No. 1 in Table 9.1 shows that at time 0 min, the distance moved is also zero. The point corresponding to this set of values on the graph will, therefore, be the origin itself. After 1 minute, the car has moved a distance of 1 km (see S.No. 2). Mark one point (as pencil dot) on the graph paper where the graph lines representing these two values meet. Similarly, mark in the graph paper the points (as pencil dots) corresponding to the different sets of values. 6. Join all the marked points (or pencil dots) with a pencil line. It is a straight line in this case. This is the distance-time graph for the motion of the car (Figure 9.9). ## Distance-Time Graph for Various Forms of Motion 1. **Distance-time graph for uniform motion [or uniform (constant) speed]:** When the distance-time graph is a straight line, it indicates that the object is moving at a constant speed (or in uniform motion) (Figure 9.10). The slope of a distance-time graph indicates the speed of the object. 2. **Distance-time graph for a non-uniform motion (or changing speed):** When the distance-time graph is a curved line, it indicates that the object is moving with a non-uniform speed (or changing speed) (Figure 9.11). The speed of the moving object is not uniform. 3. **Distance-time graph when the object is stationary (at rest):** After travelling a certain distance, when a moving object stops and comes to rest, then the distance-time graph is a straight line parallel to the time-axis (or X-axis) (Figure 9.12). The speed of the object is zero. ## Assertion-Reason based Questions *Reasoning* In the following questions, two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answers to these questions from the codes (a), (b), (c) and (d) as given below. -(a) Both A and R are true and R is the correct explanation of the assertion. -(b) Both A and R are true but R is not the correct explanation of the assertion. -(c) A is true but R is false. -(d) A is false but R is true. 1. Assertion: Modern-day watches use quartz crystal instead of pendulums for measuring time. Reason: Quartz clocks or watches measure time more accurately. 2. Assertion: The motion of a car with constant speed along a straight line is considered a non-uniform motion. Reason: An object moving along a straight line with constant speed is said to have a uniform motion. 3. Assertion: A person sitting in a moving train appears to be at rest to another person sitting next to him. Reason: An object is said to be at rest when it does not change its position with respect to its surroundings. ## Complete the Flowchart for Revision **MOTION** **PERIODIC MOTION** - Simple - example - Frequency **DISTANCE TRAVELLED AND TIME TAKEN** - -time graph - Curved line **SPEED (DISTANCE TRAVELLED PER UNIT TIME)** - Non-uniform motion, Examples - Uniform motion, Examples ## Competency Based Discussion: Measurement of Time- Then and Now ## Exercise *According to NEP Guidelines* **A. Oral Questions:** 1. What is the use of knowing your walking speed? 2. You are running along a circular path. Will your motion always be periodic? **B. Science Riddles:** 1. I am always in motion, yet I never move. What am I? 2. I am the smallest measure of time, but I am not a clock. What am I? **C. Multiple Choice Questions:** *Applying, Analysing* Tick (✔) the correct options. 1. A person starts riding at 9:00 am to reach a location that is about 175 km away from the starting point. He drives at an average speed of 70 km/hr. When is the person likely to reach his destination? - 10:00 am - 10:30 am - 11:00 am - 11:30 am 2. Richa notices the swing of a pendulum as shown in Figure A. She notices that the bob of the pendulum starts from position A to C and come back to A in 2 seconds. What is the time period of the pendulum? - 1 second - 2 seconds - 4 seconds 3. The time and position of a moving car covering a distance of 3 km is shown in the image. What can be concluded from the position of the car? - It was moving at a uniform speed of 60 km/hr - It was moving at a non-uniform speed of 60 km/hr - It was moving at uniform speed as it covered 3 km in 3 min - It was moving at non-uniform speed as it covers 3 km in 3 min 4. The distance between Mysore and Srirangapatnam is about 100 km and the time taken to reach from Mysore to Srirangapatnam is 4 hrs. Calculate the average speed of the train (km/h) while travelling between the two stations. - 20 km/hr - 25 km/hr - 30 km/hr - 50 km/hr 5. A student wants to measure the speed of a ball rolling down a ramp. He found a few instruments which are listed in the table A. Which of these are required to measure the speed of the ball? - Hourglass and thermometer - Balance scale and stopwatch - Only stopwatch - Measuring tape and thermometer 6. The table B lists a few motions which relate to measuring time. Which of these motions can be considered as a periodic motion? - Only P - Only Q - Both P and Q - Both Q and R **D. Case/Source based Questions:** *Understanding, Applying, Analysing* Observe the graph carefully and answer the questions that follow. Soham goes to the football ground to play football. The distance-time graph of his journey from his home to the ground is shown in the graph. 1. What does the graph between the points B and C indicate about the motion of Soham? - Soham is at rest. - Soham is moving at a constant speed. - Soham is in uniform motion. - Soham is in non-uniform motion. 2. The speed of Soham between 8 and 12 minutes of his journey is - 18.75 m/min - 19.75 m/min - zero - 2.7 m/min 3. During which time period Sohan showed the highest speed? **A. Very Short Answer Questions:** *Understanding, Reasoning* 1. What kind of watch will you use to accurately measure short intervals of time? 2. The weight of a pendulum-bob is doubled. What will happens to its time period? 3. Which one is better to use for measuring time- a water clock or a sundial? Give a reason. **B. Short Answer Questions:** *Understanding, Reasoning, Analysing* 1. State the principle used for measuring time in watches and clocks. 2. Rahul switches off a fan and the fan blades start to slow down. Is the motion of the fan periodic in this case? Why/Why not? 3. A few activities are shown in the given images. Which of these motions are oscillatory in nature? Give a reason in each case. 4. A train is moving with constant speed. It stops after some time when the brake is applied. How does the speed of train change? Is the motion during braking- uniform or non-uniform? Give a reason. **C. Long Answer Questions:** *Logical Thinking, Applying* 1. In a distance time graph based on the motion of a car- - What type of motion does a car show which is not moving with a constant speed? - What type of motion does a straight line represents? - How is the average speed of the car different from its speed? 2. When two objects are moving with same speed but in different directions, how will you determine which one is moving faster? Draw a distance time graph to show their motion. 3. The three graphs P, Q and R are speed vs time graphs of three cars. - Identify the graphs from the clues and give a reason for the answer. - Mr Sharma is a gentle driver. He lets the car pick up speed slowly. - Ms Bala sometimes goes on a drive on an empty road. She enjoys cruising along at the same speed. 2- Ms Reema is a racing car driver. She has just started a race. 4. Radhika travelled from Lucknow to Ghaziabad by car for a distance of 512 km. She started at 8am from Lucknow and drove at an uniform speed of 80 km/hr. She took a halt after 140 km from 9 am to 9:30 am and then drove at a speed of 100 km/hr till the next 400 km. Find out the total time taken to travel. 5. A car starts from rest at 5.00 pm. The distances covered by the car at various instants of time are recorded as follows: | Time (pm) | Distance (km) | |---|---| | 5.00 | 0 | | 5.30 | 30 | | 6.00 | 60 | | 6.30 | 90 | | 7.00 | 120 | | 7.30 | 150 | - Draw a distance-time graph for the given data. - What distance was covered by the car at 6.15 pm? **D. Application Based Questions:** 1. You are going to Mathura by car. You look at a milestone that reads 'Mathura 4 km away' at 4:00 pm. At 4:05 pm you see a milestone that reads 'Mathura 1 km away'. What is the speed of your car in km/minute? 2. You are drawing water from a well. The speed at which you pull the bucket out is 0.5 m/s. It takes 5 seconds to pull out the bucket. What is the length of the rope? (Assume that no part of the rope is hanging out when you start pulling it.) 3. A car moves at a speed of 20 km/h for 15 minutes and then at a speed of 60 km/h for the next 15 minutes. Calculate the total distance covered by the car. 4. During an experiment, object A covers a distance of 50 m in 10 s, while object B covers the same distance in 20 s. Find the ratio of the speed of object A to the speed of object B. Also, calculate the difference between their speeds. ## Enrichment Activities *According to NEP Guidelines* **Digital Learning** Research on the Internet about biological processes in the body of some animals that are nearly periodic. Write a journal on it. **Critical Thinking** How would you go through your day if you had no instrument for measuring time? Write a diary entry and show it to your teacher. **Extended Learning** *NEP Guidelines* **Story time:** Once upon a time there were two good friends, the rabbit and the tortoise. They decided one day to have a race amongst them to find who was the fastest. The starting point was decided as the mango tree and the finishing point was the pond. The distance between the two points was 500 m. The squirrel blowed the whistle and the race started. The tortoise, according to its nature, walked slowly whereas the rabbit ran fast and reached the middle point (250 m) within 15 mins where there was a neem tree. He looked at the tortoise left far behind and thought of taking a nap as he knew he would win, but the tortoise kept on walking continuously. The tortoise reached the midpoint after 15 mins of the rabbit reaching it. It kept on walking and walking and reached the end point in 1 hour from the starting point. Then the rabbit woke up, looked back to find the tortoise but he realised that his friend had won the race. - Who amongst the two was running faster? - Who moved in slow motion? - On what basis do we decide whether the tortoise is running fast or slow? - What do you learn from the story? ## My Progress Card | S.No. | Topics | I understand | I do not understand | |---|---|---|---| | 1. | Measurement of Time in Ancient Times | | | | 2. | Measurement of Time | | | | 3. | Unit of Time, Motion, Speed | | | | 4. | Numerical Problems Based on Speed | | | | 5. | Uniform and Non-uniform Motion | | | | 6. | | | | | 7. | | | | | | | | |