Work and Energy 9 Science — Revision Notes
Work is done when force causes displacement in its direction. Energy is capacity to do work, and understanding energy conservation and transformation is ke
TL;DR: Work is done when force causes displacement in its direction. Energy is capacity to do work, and understanding energy conservation and transformation…
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Work is done when force causes displacement in its direction. Energy is capacity to do work, and understanding energy conservation and transformation is ke
Work and Power
- Work = Force × Displacement × cos(θ), where θ is angle between force and displacement
- Work done is zero if force is perpendicular to displacement
- Power = Work/Time, measured in watts (W)
- 1 watt = 1 joule per second
Kinetic and Potential Energy
- Kinetic energy: KE = 1/2 mv², energy of motion
- Potential energy: PE = mgh, energy of position relative to reference point
- Elastic potential energy stored in springs: PE = 1/2 kx²
Law of Conservation of Energy
- Total mechanical energy (KE + PE) remains constant in isolated systems
- Energy cannot be created or destroyed, only transformed
- At highest point of motion, all energy is potential; at lowest point, mostly kinetic
Energy Transformations
- Falling object: PE converts to KE, total energy constant
- Bouncing ball: KE converts to PE on impact, some lost as heat/sound
- Pendulum: oscillates between maximum PE and maximum KE at lowest point
Key Terms
- Work: Force applied over distance in direction of force (unit: joule)
- Energy: Capacity to do work
- Kinetic Energy: Energy due to motion of object
- Potential Energy: Energy due to position or configuration of object
- Power: Rate of doing work (unit: watt)
Frequently Asked Questions
Can work be negative?
Yes, when force opposes displacement (angle > 90°), work is negative, reducing object's energy.
Why is energy conserved but work can vary?
Energy is conserved in total, but work done by different forces varies; sum of work equals change in kinetic energy.
What happens to mechanical energy when friction acts?
Friction converts mechanical energy to heat; total energy is conserved but mechanical energy decreases.
More 9 Science Revision Notes
- Matter in Our Surroundings
- Is Matter Around Us Pure
- Atoms and Molecules
- Structure of the Atom
- The Fundamental Unit of Life
- Force and Laws of Motion
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