Question
Compare and contrast kinetic and potential energy.
Answer
Kinetic energy and potential energy are both forms of energy, are measured in joules, and can be converted into one another. They differ in what property of a system stores the energy.
| Feature | Kinetic energy | Potential energy |
|---|---|---|
| Physical basis | Motion | Relative position, arrangement, composition, or condition |
| Common macroscopic model | for translational motion | near Earth's surface; for an ideal spring |
| Microscopic examples | Translational, rotational, and vibrational motion of particles | Energy associated with interactions among particles, charges, nuclei, or bonds |
| Reference dependence | A speed must be measured in a chosen reference frame | A zero of potential energy must be chosen for the interaction |
In a mechanical system, energy may shift between kinetic and potential forms. As an ideal pendulum moves downward, gravitational potential energy decreases while kinetic energy increases. At the lowest point, its speed and kinetic energy are greatest; at a turning point, its speed is zero and its gravitational potential energy is greatest relative to the chosen zero.
In chemistry, the internal energy of a sample includes microscopic kinetic and potential contributions. Temperature tracks average molecular kinetic energy in the relevant model, while changes in molecular arrangement or interactions can change potential energy. During a phase change, energy can change the arrangement of particles even while the temperature remains constant.
The total energy of an isolated system is conserved. Kinetic and potential energy may change individually while energy is transferred between forms or to other forms such as thermal energy.
Evidence boundary
This is a conceptual comparison. No particular system, zero of potential energy, or numerical process is specified. The equations shown are standard models with limited domains: mgh assumes a nearly uniform gravitational field, and 1/2 kx^2 assumes an ideal linear spring. Microscopic potential energy depends on the interactions included in the chosen model.
Sources
These references support the concepts and methods used in the explanation above.