Class 9 Science Chapter 7 Work, Energy and Simple Machines – Revision Notes

Quick revision notes for Class 9 Science Chapter 7 (Work, Energy and Simple Machines). These Class 9 Science Chapter 7 notes are ideal for quick revision just before exams.

Work

• W = F × d (force × displacement in direction of force).
• No displacement or perpendicular displacement = no work.

Energy

• KE = ½mv² (kinetic, motion).
• PE = mgh (gravitational potential).
• Work-energy theorem: net work = change in KE.
• Conservation of energy: total energy constant, only transforms.

Power

• P = W/t; SI unit: watt (W).

Simple Machines

• Mechanical advantage = load/effort.
• Pulleys: change force direction; multiply effort with multiple pulleys.
• Inclined plane: trades distance for reduced force.
• Lever: multiplies force via fulcrum placement.
• Machines don’t reduce total work (ignoring friction) — they trade force for distance.

One-Line Summary

Work (force × displacement) links to kinetic and potential energy through the work-energy theorem and conservation of energy, power measures how fast work is done, and simple machines make tasks easier by trading force for distance without changing total work.

Written by Satish

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