Conservation of Energy

The conservation of energy tells us that in a closed system, the total amount of energy stays the same even though it can change form, such as from motion to heat or from chemical to electrical energy. This works because energy is a bookkeeping quantity: interactions can move it around or convert it, but they do not make it appear from nothing or vanish on their own. In physics, this principle is deeply connected to the symmetry of nature in time, and it is one of the most reliable tools for predicting how systems behave.

Use this formula when you want to track how energy changes in a system without being lost to the outside, such as in mechanics, circuits, heat transfer, or chemical processes. It is especially useful for finding speeds, heights, temperatures, or amounts of work when different energy forms are involved.

• Forgetting that energy conservation applies to the whole system, not necessarily to one object alone
• Mixing up energy forms and treating potential energy as if it were always gravitational potential energy
• Ignoring energy losses like friction, air resistance, or heat when the problem says the system is not perfectly isolated