NCERT Solutions for CBSE Class 7 Science Chapter 9: Motion and Time

The NCERT textbook for CBSE Class 7 Science Chapter 9 Motion and Time begins by establishing how we perceive and compare motion. An object is in motion when it changes position with respect to a reference point over time. Slow and fast are relative terms that describe the rate at which this position change occurs. A snail crawling across a leaf exhibits slow motion, covering perhaps 5 centimetres in one minute, while a car on a highway demonstrates fast motion, covering 20 kilometres in the same duration. The chapter emphasizes that we cannot call motion 'slow' or 'fast' without comparison — a bicycle moving at 15 km/h is fast compared to a walking person (5 km/h) but slow compared to a motorcycle (60 km/h). Students learn that this comparison requires measuring both distance travelled and time taken, leading naturally to the concept of speed. Questions in this section typically ask students to arrange objects in order of increasing or decreasing speed based on given distance and time data, testing their ability to perform basic comparisons before formal speed calculations.

CBSE Class 7 Science Chapter 9 Motion and Time introduces uniform motion as motion in which an object covers equal distances in equal intervals of time, regardless of how small those intervals are. If a car travels exactly 10 metres every second for the duration of its journey, it exhibits uniform motion. Non-uniform motion, conversely, occurs when an object covers unequal distances in equal time intervals — a city bus that stops at traffic signals, speeds up, and slows down demonstrates non-uniform motion. The NCERT textbook clarifies that most everyday motion is non-uniform; truly uniform motion is rare in nature but serves as an important idealized concept in physics. Students must understand that for uniform motion, speed remains constant throughout the journey, while in non-uniform motion, speed varies continuously. This distinction becomes critical when students calculate average speed — for uniform motion, speed at any instant equals average speed; for non-uniform motion, we can only calculate average speed over the entire journey. Examination questions frequently present scenarios and ask students to classify the motion as uniform or non-uniform with justification.

The central quantitative concept in CBSE Class 7 Science Chapter 9 Motion and Time is speed, defined as the distance travelled per unit time. The NCERT textbook presents the formula: Speed = Distance/Time. The SI unit of speed is metre per second (m/s), obtained when distance is measured in metres and time in seconds. However, for vehicles and long-distance travel, kilometre per hour (km/h) is more practical. Students must master converting between these units: 1 km/h = 5/18 m/s, and 1 m/s = 18/5 km/h = 3.6 km/h. Most NCERT questions in this chapter involve calculating speed when distance and time are given, or finding distance when speed and time are provided, or determining time when speed and distance are known. The chapter emphasizes that for non-uniform motion, we calculate average speed using total distance and total time. A common error students make is using the formula incorrectly with mismatched units — adding distance in kilometres to time in seconds without conversion. Practice with unit conversion is essential, as examination questions deliberately mix units to test understanding.

CBSE Class 7 Science Chapter 9 Motion and Time introduces distance-time graphs as a powerful visual tool to represent and analyze motion. In these graphs, time is plotted on the horizontal axis (x-axis) and distance on the vertical axis (y-axis). For uniform motion, the graph is a straight line because equal distances are covered in equal times, producing a constant ratio (constant speed). The slope or steepness of this line represents speed — a steeper line indicates higher speed, while a gentler slope shows slower motion. For non-uniform motion, the graph is a curved line because the distance covered in each time interval changes. Students learn to extract information from these graphs: the distance covered in a specific time interval, the time taken to cover a certain distance, and whether motion is uniform (straight line) or non-uniform (curved line). NCERT questions ask students to draw distance-time graphs from given data tables and interpret existing graphs to answer questions about the motion depicted. Understanding that the slope of a distance-time graph represents speed is crucial for Class 8 and Class 9 physics.

The NCERT textbook for CBSE Class 7 Science Chapter 9 Motion and Time dedicates a section to the simple pendulum as a device for measuring time. A simple pendulum consists of a small metallic ball (bob) suspended by a thread from a fixed support. When displaced and released, it swings back and forth in a regular, repeating motion called oscillation. The time taken for one complete oscillation (from one extreme position to the other and back) is called the time period. The chapter explains that for a given pendulum length, the time period remains constant, making it suitable for time measurement. Historically, pendulum clocks were the most accurate timekeeping devices from the 1600s until the 1930s. Students learn that the time period of a simple pendulum depends primarily on its length — longer pendulums have longer time periods, shorter ones swing faster. The chapter includes activities where students measure the time for multiple oscillations (say, 20 swings) and divide by the number to find the time period for one oscillation, reducing measurement error. Questions ask about factors affecting pendulum motion and why it was useful for timekeeping.

The end-of-chapter exercises in CBSE Class 7 Science Chapter 9 Motion and Time contain approximately 10-12 questions covering all concepts taught. These include conceptual questions requiring short written answers, numerical problems involving speed calculations, questions about interpreting or drawing distance-time graphs, and application-based scenarios. Question 1 typically asks students to classify given examples as slow or fast motion. Question 2 often involves distinguishing uniform from non-uniform motion in daily-life scenarios. Questions 3-5 usually present numerical problems: calculating speed when distance and time are given, finding distance when speed and duration are provided, or determining time taken for a journey at a specified speed. Question 6 commonly asks students to convert speeds between km/h and m/s. Questions 7-8 involve distance-time graphs — either plotting data points and drawing the graph, or interpreting a given graph to extract information about the journey. Questions 9-10 relate to the simple pendulum, asking about factors affecting its motion or how it measures time. Question 11 might ask why the odometer and speedometer in vehicles show different types of information. The final questions often require applying multiple concepts together, such as comparing average speeds of two objects that travel different distances in different times.

When solving questions from CBSE Class 7 Science Chapter 9 Motion and Time, students frequently make predictable errors that cost marks in examinations. The most common mistake is mixing units without conversion — using kilometres for distance and seconds for time in the speed formula, yielding meaningless results. Always convert to matching units first: either both in SI units (metres and seconds) or both in practical units (kilometres and hours). Another frequent error is confusing speed with distance or time in word problems; carefully identify what is given and what is asked before selecting the formula. In distance-time graphs, students sometimes plot time on the y-axis and distance on the x-axis (reversed), producing incorrect interpretations. Remember: time always goes on the horizontal x-axis. When calculating average speed for journeys with multiple segments, students often average the speeds rather than using total distance divided by total time — these give different results. For pendulum questions, students sometimes think the mass of the bob affects the time period; experiments show it does not, only length matters (for small oscillations). Finally, in questions asking to classify motion as uniform or non-uniform, students must check if equal distances are covered in equal times, not just if speed is high or low.

CBSE Class 7 Science Chapter 9 Motion and Time includes several important numerical problems that appear frequently in school examinations and require methodical problem-solving. One classic question type provides distance and time for two different objects and asks which is faster — students must calculate both speeds and compare numerically. Another common problem gives speed in one unit (say, m/s) and asks for conversion to another unit (km/h), testing unit conversion skills. A third type presents a journey in multiple segments with different speeds and asks for average speed over the entire journey — this requires calculating total distance and total time separately before dividing. Graph-related numericals provide a table of distance and time values, asking students to plot the graph and determine if motion is uniform, then calculate speed from the graph's slope. Pendulum problems typically give the time for multiple oscillations and ask for the time period of one oscillation, or vice versa. Each problem should be solved in four clear steps: (1) write down given values with correct units, (2) write the formula needed, (3) substitute values and perform the calculation, (4) write the answer with appropriate units and check reasonableness.

Understanding distance-time graphs in CBSE Class 7 Science Chapter 9 Motion and Time lays essential groundwork for velocity-time graphs and acceleration concepts in Classes 9 and 11. In Class 7, students learn that the slope of a distance-time graph represents speed; this same principle extends to Class 9 where the slope of a velocity-time graph represents acceleration. The ability to interpret the shape of a graph — recognizing that a straight line means constant rate and a curve means changing rate — transfers directly to kinematics in higher classes. When Class 9 introduces the three equations of motion (v = u + at, s = ut + ½at², v² = u² + 2as), students who thoroughly understood distance-time relationships in Class 7 find these much easier to grasp. The NCERT Class 7 chapter deliberately avoids the term 'velocity' (using only 'speed'), but the graphing skills learned here are identical to those needed for velocity-time analysis later. Similarly, the concept that area under a graph can represent a physical quantity (which students will use in Class 11 to find displacement from velocity-time graphs) has its roots in the graph interpretation skills developed in this chapter. Students aiming for science stream in Classes 11-12 should master this chapter's graphs thoroughly.

Unit conversion between km/h and m/s is a critical skill tested repeatedly in CBSE Class 7 Science Chapter 9 Motion and Time examinations. The conversion arises because SI units use metres and seconds, while everyday vehicle speeds use kilometres and hours. To convert km/h to m/s, multiply by 5/18 (or divide by 18 and multiply by 5). This works because 1 km = 1000 m and 1 hour = 3600 seconds, so 1 km/h = 1000 m / 3600 s = 5/18 m/s. Conversely, to convert m/s to km/h, multiply by 18/5 or 3.6. Students should memorize these conversion factors rather than deriving them each time during exams. A good practice method is to convert common speeds both ways: 36 km/h = 36 × 5/18 = 10 m/s; 20 m/s = 20 × 18/5 = 72 km/h. Questions often provide speed in one unit and ask for the answer in another unit, or give mixed data (distance in km, time in seconds) requiring conversion before calculation. Examiners specifically design such questions to test whether students blindly apply formulas or understand what the numbers represent. Marks are deducted if the final answer has incorrect or missing units.

CBSE Class 7 Science Chapter 9 Motion and Time teaches concepts that students encounter daily in the real world, making this one of the most practically relevant chapters in the curriculum. Every time a family checks Google Maps for estimated arrival time, the app calculates average speed based on current traffic (distance divided by expected time). When news reports a speeding violation, the concept of speed limits (measured in km/h) and measurement using radar or cameras applies the same principles. Athletes and coaches use precise time measurement to track performance improvements — a sprinter reducing their 100-metre time from 12.5 seconds to 12.2 seconds has increased average speed from 8 m/s to 8.2 m/s. Transportation planning relies on distance-time analysis: train schedules, flight durations, and delivery estimates all depend on calculating time from distance and average speed. Understanding uniform versus non-uniform motion helps interpret fuel efficiency — a car in stop-and-go city traffic (non-uniform motion) consumes more fuel per kilometre than the same car on a highway at steady speed (uniform motion). Even fitness trackers and smartphone apps that count steps and estimate calories use motion detection and time tracking, applying this chapter's foundational concepts through built-in sensors.

Many Class 7 students struggle with CBSE Class 7 Science Chapter 9 Motion and Time because it introduces quantitative physics for the first time, requiring both conceptual understanding and numerical problem-solving skills. CBSETUTOR.ai provides 24×7 AI tutoring that has ingested the complete NCERT Class 7 Science textbook, including every example and exercise from Chapter 9. When a student gets stuck on a speed calculation or cannot interpret a distance-time graph, they can photograph their worksheet or textbook question and upload it to CBSETUTOR.ai. The AI tutor provides step-by-step solutions aligned precisely with NCERT methodology — showing unit conversions explicitly, explaining which formula to use and why, and helping students identify their specific error (whether it is a calculation mistake, unit confusion, or conceptual misunderstanding). Unlike generic video tutorials that cover topics broadly, the AI tutor adapts to each student's specific doubt in real-time. For example, if a student repeatedly makes unit conversion errors, the tutor provides extra practice problems focused on km/h to m/s conversions. Parents across India find that at ₹999 per month (one flat price covering all subjects for Classes 6-12), CBSETUTOR.ai provides personalized support equivalent to an on-demand home tutor but available anytime their child needs help, whether at 6 AM before school or 11 PM while completing homework. A three-day free trial requires no credit card, allowing families to experience how AI tutoring builds genuine understanding of motion, speed, and time measurement.

CBSE Class 7 Science Chapter 9 Motion and Time typically carries 10-12 marks in school term examinations and 8-10 marks in the annual exam, distributed across short-answer (2-3 marks), numerical problems (3-4 marks), and one graph question (4-5 marks). To score full marks, students must follow specific strategies that align with CBSE marking schemes. For conceptual questions asking to 'differentiate' or 'define', write answers in structured points — examiners award marks for each distinct correct point mentioned. For numerical problems, always follow the four-step method: write given values with units, state the formula, show substitution with numbers, and write the final answer with correct units. Even if the final answer is wrong, you can earn partial marks (1-2 out of 3-4) for correct method. Never write just the final number without showing working. For distance-time graph questions, use a sharp pencil and ruler; freehand curves or lines cost marks. Label both axes clearly with quantities and units (for example, 'Time (seconds)' not just 'Time'). When interpreting graphs, write complete sentences — 'The graph shows uniform motion because it is a straight line, indicating constant speed' scores more than just 'uniform motion'. In 2-mark or 3-mark questions, aim to write 2-3 distinct points; single-sentence answers rarely receive full marks even if correct. Finally, allocate time proportionally: a 2-mark question deserves 2-3 minutes, a 4-mark graph question deserves 6-8 minutes. Practice previous years' question papers under timed conditions to build speed and accuracy.