Ch 12 explores friction — the force that opposes relative motion. Students learn types of friction, its causes, advantages and disadvantages, and methods to increase or reduce it.
Friction opposes the relative motion between surfaces in contact. Static friction: opposes the start of motion (highest). Sliding friction: while surfaces slide over each other. Rolling friction: while an object rolls (least). Friction depends on the nature (roughness) of surfaces and the force pressing them together.
Advantages: walking (grip), writing, braking vehicles, holding objects. Disadvantages: wears out surfaces (shoes, tyres), produces heat, slows motion. Reducing friction: lubricants (oil, grease), ball bearings, polishing surfaces, streamlined shapes (cars, planes, fish).
Download: https://ncert.nic.in/textbook/pdf/hesc112.pdf | Complete book: https://ncert.nic.in/textbook/pdf/hesc1ps.zip
Treads increase friction between the tyre and the road, especially on wet surfaces. The grooves channel water away, preventing the tyre from sliding (aquaplaning). Worn-out tyres with smooth surfaces are dangerous because they offer less grip.
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