Physics
Conservation of Energy
Quick fact
A bouncing ball never returns to its original height because some of its kinetic energy transforms into heat and sound, yet the total energy of the ball and ground system remains constant.
Why this is interesting
You’ve heard that energy is never lost, just transformed. But what does that actually mean for a bouncing ball, a burning log, or your own body?
Read the full explanation
Understanding Conservation of Energy
Imagine you have a savings account called 'energy.' Every time something happens—a ball falls, a car moves, or a plant grows—energy simply moves from one account to another. It never disappears; it just changes form. For instance, when you lift a book, you add gravitational potential energy. When you drop it, that potential energy turns into kinetic energy (motion) and then, upon impact, into sound and thermal energy. The total amount of energy in the universe stays the same. This law means you can track energy through any process, knowing that the sum before equals the sum after.
A deeper explanation
The conservation of energy is a consequence of the uniformity of time: the laws of physics don't change from one moment to the next. In any isolated system, the total energy remains constant over time. This principle applies across all scales—from subatomic particles to galaxies. It explains why perpetual motion machines are impossible: any real process inevitably converts some energy into non-recoverable forms like heat, due to friction or other dissipative forces. This law also underpins the first law of thermodynamics, which states that the change in a system's internal energy equals the heat added minus the work done. Understanding conservation helps engineers design efficient engines, scientists analyze chemical reactions, and everyone make sense of why we cannot 'create' energy, only convert it.