Conservation of Energy

The law of conservation of energy states that energy cannot be created or destroyed, but it can be converted from one form to another.
This principle is a constant across all energy conversions and transformations.
It’s integral part of all physics and can be applied to all systems, from tiny quantum particles to the vast galaxies.

A closed system is a physical system that doesn’t exchange matter with its surroundings, and isn’t subject to external force fields.
In a closed system, the total amount of energy is always conserved.
An open system can exchange both energy and matter with an external environment, thus its total energy might not be constant.

An example of the conservation of energy is a pendulum. At the highest points of its swing (end extremes), it possesses maximum potential energy but zero kinetic energy. At the lowest point (middle of its path), it exhibits maximum kinetic energy and minimum potential energy. However, the total energy remains the same.
Another example is the energy changes in a roller coaster. When the roller coaster climbs to the top of a steep hill, it has maximum potential energy. As it begins to descend, potential energy is converted into kinetic energy, reaching its peak at the bottom of the hill. Even though the type of energy is changing, the total amount of energy is conserved.

Energy transformation refers to the process of changing one form of energy to another.
In many daily activities or devices, energy conversions are common. For example, a toaster converts electrical energy into heat energy to toast bread, and a car engine turns the potential energy stored in fuel into kinetic energy that moves the vehicle.
Along with these transformations, some energy is often lost, mostly as heat due to friction or resistance. This might make it seem like energy isn’t conserved, but in reality, that energy has simply been transferred to the surroundings.

Power is the rate at which energy is converted from one form to another. It’s measured in watts (W), with one watt representing a conversion of one joule of energy per second.
Efficiency of an energy conversion device is the fraction of input energy that gets converted into useful output. The rest of the energy is often transferred in non-useful forms like heat or sound.
No real-life device is 100% efficient due to inevitable energy losses, but the conservation of energy assures that total energy is conserved, even if not all of it is usefully transformed.