Conservation of energy
High School
Definition
The principle that energy cannot be created or destroyed, only transformed from one form to another, so the total energy of an isolated system stays constant. For example, a falling object converts gravitational potential energy into kinetic energy.
Worked examples
A 2 kg ball at 5 m height has \(PE = mgh = 2 \times 10 \times 5 = 100\) J. At ground level, \(KE = \frac{1}{2}mv^2 = 100\) J.
Gravitational potential energy transforms entirely into kinetic energy; total energy stays 100 J.
A compressed spring (elastic PE) launches a cart, giving it kinetic energy as the spring releases.
Stored elastic potential energy converts to motion energy without any energy being lost or created.
Common mistakes
- Energy is lost as heat in friction, so conservation of energy is violated. → Friction converts kinetic energy to thermal energy; total energy is still conserved. Heat is a form of energy — energy changes form but the total amount remains constant.
- At the highest point of a swing, all energy disappears because velocity is zero. → At the highest point, kinetic energy is zero but potential energy is maximum; total energy is constant. Energy shifts between forms continuously — zero KE means maximum PE at that instant.
- A battery creates new energy to power a device. → A battery stores chemical potential energy and transforms it into electrical energy. Batteries don't create energy; they release energy that was stored during manufacture or charging.
Where you'll use it next
You'll apply conservation of energy to solve mechanics problems in physics, understand chemical reactions and metabolism in biology, analyze power generation and efficiency in engineering, and study thermodynamics.
Found in 1 StudyPug lesson
Conservation of energy
11th Grade11thPhysics
See also
Reviewed by Pat Cheng, M.Ed. — StudyPug Curriculum Lead · Last updated June 6, 2026