Lesson 8: Work, Energy & Power
Energy is the capacity to do work. It can never be created or destroyed — only converted from one form to another. Understanding energy conservation is fundamental to engineering, environmental science, and everyday life.
Key Concepts
Work
W = F·d·cos θ. Work is done on an object when a force causes displacement in the direction of the force. Measured in joules (J). If the force is perpendicular to motion, no work is done.
Kinetic Energy
KE = ½mv². Energy of motion. Doubling speed quadruples KE. When you do positive work on an object, its kinetic energy increases (Work-Energy Theorem: W_net = ΔKE).
Potential Energy
Stored energy. Gravitational PE = mgh (mass × g × height). Spring PE = ½kx². When an object falls, gravitational PE converts to KE.
Conservation of Energy
In a closed system with no friction: KE + PE = constant. A roller coaster at the top of a hill has maximum PE/minimum KE. At the bottom: maximum KE/minimum PE.
Power
P = W/t = F·v. The rate of doing work. Measured in watts (W = J/s). A 100W light bulb uses 100 joules every second. Horsepower is another unit: 1 hp ≈ 746 W.
🔬 Virtual Lab: Energy Conservation on a Ramp
Set the height and mass of a ball. Launch it down the ramp and watch PE convert to KE in real time with live bar charts.
✅ Check Your Understanding
1. When a ball rolls down a hill (no friction), what energy conversion occurs?
2. If you double the speed of an object, its kinetic energy:
3. Power is defined as: