Ch 11 introduces force as a push or pull that changes an object's state of motion or shape. Students classify forces into contact and non-contact types and learn about pressure.
Contact forces require physical contact: muscular force (push, pull), friction (opposes motion). Non-contact forces act from a distance: gravitational (pulls objects toward earth), electrostatic (charged objects attract/repel), magnetic (magnets attract/repel). Force can change speed, direction, or shape of an object.
Pressure = Force ÷ Area. Same force over smaller area = more pressure (why nails are pointed). Liquid/gas pressure acts in all directions. Atmospheric pressure: weight of air pressing on us (~101.3 kPa). We don't feel it because body pressure balances it.
Download: https://ncert.nic.in/textbook/pdf/hesc111.pdf | Complete book: https://ncert.nic.in/textbook/pdf/hesc1ps.zip
Camels have wide, padded feet that spread their weight over a large area, reducing pressure on the sand. Humans have small feet, concentrating weight on a small area, creating high pressure that sinks into loose sand.
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