Work, Energy & Power
The transformation and transfer of mechanical energy.
Mechanical work occurs when a force causes displacement of an object. Energy represents the capacity to perform this work, and power measures the rate of energy transfer.
This unit explores the conversion between kinetic energy (motion) and gravitational potential energy (position), culminating in the Law of Conservation of Mechanical Energy.
Key Takeaways
- •Work is a scalar quantity calculated as the dot product of force and displacement vectors.
- •Mechanical energy is conserved in systems where only conservative forces (like gravity) perform work.
- •Power is measured in Watts (Joules per second) or Horsepower.
Core Concepts & Definitions
1The Work-Energy Theorem
The net work done by external forces on a system equals the change in its total kinetic energy.
•W_net = ΔKE = KE_final - KE_initial.
•Negative work occurs when force opposes the displacement direction (e.g. friction).
2Conservative vs Non-Conservative Forces
Conservative forces (gravity, springs) conserve mechanical energy. Non-conservative forces (friction, drag) dissipate energy as heat.
•Total mechanical energy E = KE + PE.
•In conservative systems, ΔE = 0.
Quick Revision Notes
- •1 Watt = 1 Joule per second. 1 Horsepower (HP) ≈ 746 Watts.
- •Friction always does negative work on moving objects, converting mechanical energy to heat.