Key Concepts: Kinetic Energy & Potential Energy

Kinetic Energy (KE)

• The energy of motion: KE = ½mv².
• Doubles when speed doubles? No — quadruples (KE ∝ v²). Doubling speed quadruples the energy.
• Always positive or zero (never negative).

Potential Energy (PE)

• Gravitational PE: Energy due to position in a gravitational field. PE = mgh (near Earth's surface).
• Elastic PE: Energy stored in a deformed elastic object. PE = ½kx² (spring).
• Potential energy depends on a reference point — only changes in PE are physically meaningful.

Mechanical Energy

• Total mechanical energy = KE + PE.
• When only conservative forces act, mechanical energy is conserved: KE₁ + PE₁ = KE₂ + PE₂.
• A falling ball converts PE to KE. A rising ball converts KE to PE.