Ch 13 introduces quantitative measurement of motion. Students learn to calculate speed, plot distance-time graphs, and distinguish between uniform and non-uniform motion.
Speed = Distance ÷ Time. SI unit: m/s. Also used: km/h. To convert km/h to m/s, multiply by 5/18. Average speed = total distance ÷ total time. Speedometer measures speed in vehicles; odometer measures distance.
Plot time on x-axis and distance on y-axis. Straight line through origin = uniform speed. Steeper line = higher speed. Curved line = non-uniform speed (speed changes). Horizontal line = object at rest.
Download: https://ncert.nic.in/textbook/pdf/gesc113.pdf | Complete book: https://ncert.nic.in/textbook/pdf/gesc1ps.zip
Speed is how fast an object moves (distance/time) — it has no direction. Velocity includes direction (displacement/time). A car going 60 km/h is speed; going 60 km/h north is velocity. This distinction is covered in detail in Class 9.
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