Physics 11 · Physics · Lesson 5.2
Mechanical Energy & Conservation
- Level
- Grade 11
- Reading time
- 12 min reading
- Review
- Last reviewed 2026-09-03
- Standard
- Accuracy standard
- Errata
Abstract
Kinetic and potential energy.
What is the conservation of mechanical energy?
Short answer
The conservation of mechanical energy states that when only conservative forces like gravity act, the total mechanical energy — kinetic plus potential — of a system stays constant. Energy converts between kinetic and potential forms, but the sum does not change. Friction and other non-conservative forces transfer some of it to thermal energy, so mechanical energy is then no longer conserved.
Concept preview
What you will be able to do
- 01Calculate kinetic energy (½mv²) and gravitational potential energy (mgh)
- 02Apply the work–energy theorem (W_net = ΔKE)
- 03Use conservation of mechanical energy to solve motion problems
An object can carry mechanical energy in exactly two ways: because it is moving (kinetic energy) or because of its position (potential energy). Their sum is the total mechanical energy, . Almost every mechanics problem in this chapter is really about energy sloshing back and forth between these two stores.
School Plan
Mechanical Energy & Conservation
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Related topics
Frequently asked questions
- When is mechanical energy not conserved?
- When non-conservative forces such as friction or air resistance act, they convert some mechanical energy into heat, so the mechanical total drops.
- What are the two forms of mechanical energy?
- Kinetic energy (energy of motion) and potential energy (stored energy, such as gravitational potential energy).