Energy is one of the most fundamental concepts in physics. It represents the capacity to do work or cause change in any system. Energy is a scalar quantity, meaning it has magnitude but no direction, and it is measured in joules in the International System of Units. We can see energy in motion, like a moving ball, or stored in systems, like a compressed spring.
Energy exists in many different forms throughout the physical world. The two fundamental categories are kinetic energy, which is the energy of motion, and potential energy, which is stored energy. Kinetic energy depends on mass and velocity squared, as shown by the formula KE equals one-half m v squared. Potential energy includes gravitational potential energy, which depends on height, and elastic potential energy in springs. Other important forms include chemical energy in batteries, electromagnetic energy in light, and nuclear energy in atomic reactions.
The Law of Conservation of Energy is one of the most fundamental principles in physics. It states that energy cannot be created or destroyed, only transformed from one form to another. The total energy of an isolated system remains constant. We can see this in a pendulum, where kinetic energy and potential energy continuously transform into each other, but their sum stays the same. Einstein's famous equation E equals m c squared shows that mass and energy are equivalent and interchangeable.
Kinetic energy is the energy of motion, described by the formula KE equals one-half m v squared. The velocity has a squared relationship, meaning that doubling the speed quadruples the kinetic energy. We see kinetic energy everywhere: in moving vehicles, flowing water that powers hydroelectric plants, wind that turns turbines, and even in the molecular motion of gases. Rotational kinetic energy follows a similar principle but uses moment of inertia and angular velocity.
Potential energy is stored energy that can be released to do work. Gravitational potential energy depends on height and is given by m g h. Elastic potential energy is stored in compressed or stretched springs, following the formula one-half k x squared. Chemical potential energy is stored in batteries, fuel, and food. Electrical potential energy exists in capacitors and electric fields. When released, all these forms of stored energy convert to kinetic energy, demonstrating energy transformation in action.