Revision Notes -Chapter 13 – Motion and Time
Distance- Defined as the total length of the path travelled, regardless of direction. It can be calculated by multiplying speed by time and is measured in metres (m) or kilometres (km).
Displacement- Represents the shortest path between the starting point and the end point, measured along a straight line. It may be shorter than the distance travelled, especially in cases where the path taken is curved or circular. Displacement is zero if you return to the starting point.
Motion- Describes the change in position of an object over time. An object is in motion if its position changes with respect to its surroundings and time.
Object at Rest- An object is at rest if it does not change its position over time relative to its surroundings.
Speed- Indicates how fast an object is moving, calculated as distance divided by time, and is measured in metres per second (m/s).
Rectilinear/Translatory Motion- Occurs when an object moves in a straight line without turning or curving.
Class 7 science -Chapter 13 – Motion and Time- Complete Notes
Circular Motion- Involves an object moving in a circle around a fixed centre point, maintaining a constant distance from the centre.
Periodic/Oscillatory Motion- Occurs when an object moves back and forth in a regular pattern over equal time intervals, like a pendulum or a swing.
NCERT Exemplar Solutions- Class 7 Science- Chapter 13 – Motion and Time
Speed Definition-
- Speed is the rate at which an object moves, calculated as distance divided by time. The formula is Speed = Total distance covered / Total time taken.
Units of Speed-
- The primary unit of speed is metres per second (m/s). It can also be expressed as kilometres per hour (km/h) or metres per minute (m/min), always using singular units (e.g., 50 km/h).
Average Speed-
- Average speed accounts for the total distance over the total time, even if the speed varies during the journey.
Slow vs. Fast Motion-
- Motion is relative; an object is considered moving faster if it covers more distance in the same amount of time compared to another.
NCERT Solutions for Class 7 Science Chapter 13-Motion and Time
Measuring Speed-
- Instruments like odometers measure the total distance, whereas speedometers indicate the instantaneous speed.
Calculating Speed-
- Speed calculation involves dividing the total distance by the total time. For example, a car travelling 100 km in 2 hours has an average speed of 50 km/h.
Also Check – Chapter 9 – Motion and Time – 4 Worksheets Solved and Unsolved
Non-uniform vs. Uniform Motion-
- Non-uniform motion occurs when an object’s speed changes due to acceleration, deceleration, or directional changes, as seen in everyday scenarios like a car approaching a stoplight.
- Uniform motion is when an object maintains a constant speed, covering equal distances in equal time intervals, less common due to external forces like friction or air resistance.
Measuring Time-
- Time measurement is crucial for understanding motion. Methods have evolved from observing natural phenomena to using complex devices.
Estimating Time in the Past-
- Shadows- Length and direction of shadows, changing with the sun’s position, were early time indicators.
- Natural Events- Regular occurrences like sunrise marked new days.
Natural Time Measurement-
- Day- Defined from sunrise to sunrise, based on Earth’s rotation.
- Month- Based on the lunar cycle from new moon to new moon.
- Year- The time for Earth to orbit the Sun, marked by seasonal changes.
Measuring Shorter Intervals-
- Shorter intervals led to the development of sundials and water clocks before modern timekeeping devices.
Simple Pendulum-
- Composition- Consists of a heavy bob attached to a thread.
- Rest Position- Known as the mean position when the pendulum hangs directly downward.
- Movement- Exhibits ‘to and fro’ motion, influenced by gravity.
- Oscillatory Motion- One oscillation includes the path from one side to the other and back.
- Time Period- The duration of one oscillation, which is consistent for small amplitudes.
Historical Methods-
- Sundials- Use the shadow of a gnomon to indicate time on a marked surface.
- Water Clocks- Measure time by the flow of water between containers.
- Hourglasses- Use sand flowing through a narrow passage to mark fixed time intervals.
Modern Clocks-
- Pendulum Clocks- Keep time using the regular swings of a pendulum.
- Quartz Clocks- Rely on the consistent vibration of quartz crystals.
- Atomic Clocks- Utilise atomic vibrations, primarily of cesium, to define the second with high precision.
Units of Time and Speed-
- Basic Unit of Time- The second (s), with larger units including minutes (min) and hours (h), where 60 seconds equal a minute and 60 minutes equal an hour.
- Basic Unit of Speed- Meter per second (m/s), with alternative units such as metres per minute (m/min) and kilometres per hour (km/h).
Understanding Time and Speed in Context-
- Time Calculations- Include converting seconds to days and hours to years.
- Practical Use- Age is typically expressed in years, whereas short durations like travel time are not.
- Perception of Time- Estimating one second by saying “two thousand and one” or by the number of heartbeats.
Measurement of Time Intervals-
- Small Intervals- Standard clocks measure down to one second; advanced clocks measure microseconds (one-millionth of a second) and nanoseconds (one-billionth of a second).
- Large Intervals- Historically in centuries or millenniums, and in astronomy, the ages of celestial bodies are in billions of years.
Types of Graphs-
- Bar Graph- Utilises rectangular bars to represent data. The height or length of each bar correlates with the value it represents, making it ideal for comparison.
- Pie Chart- Comprises sectors of a circle, each depicting a proportion of the whole. It’s useful for showing percentages and divisions of a total.
- Line Graph- Connects data points with lines, excellent for observing trends and changes over time.
Distance-Time Graphs-
- Construction- Involves plotting distance on the y-axis and time on the x-axis. The graph’s slope indicates the object’s speed; steeper means faster.
- Uniform Motion- Illustrated by a straight line.
- Non-Uniform Motion- Shown by a curved line, indicating acceleration or deceleration.
Chapter 13 – Motion and Time–Class 7 science- Question and Answer (Fill in the Blanks)
Non-Uniform and Uniform Motion – for Upper Primary School Students
Chapter 13- Motion and Time–Class 7 science- Question and Answer (Solved MCQs)
Class 7 – Science- Chapter 13- Motion and Time- Question Answer (Long Question Answer)
Class 7 -Science- Chapter 13- Motion and Time Question Answer (Short Question Answer)
