Energy – Forces, Fields, Interactions
The idea of energy may be useful in theoretical physics, but it is not a very tangible concept. Here, an older term may be more useful that is used both in physics and in everyday language: force.
Physicists consider everything that triggers a change in speed as a force. Figure skaters use muscle force to push their bodies up from the ground and then are pulled back onto the ice by gravitational force. They skate elegantly by taking advantage of the interaction between gravitational force, the inner forces of the ice, and the ice skates. Forces also interact between the sun and the planets of the universe and also between an electron and an atomic nucleus.
All known forces, such as muscle force, explosive force, friction force, buoyancy, and magnetism, can actually be derived from the four fundamental forces: gravitational, electromagnetic, and two different kinds of nuclear forces, which act over comparatively short distances.
Gravitation is the only one of the four fundamental forces that affects all objects in the universe, as gravitation is a direct result of the spatial and temporal structure. In contrast, the electromagnetic interactions only affect electrically charged particles (electrons) or objects (magnets).
Fields
Before discussing topics such as heat, work, or tsunamis, we need to first consider the third concept that, besides energy and force, fields exist to describe physical processes. Electric, magnetic, and gravitational fields are everywhere. They summarize in easily understandable ways how forces influence a particle at a certain point.
The relationship between energy, force, and a field can best be explained by an example: An electron with the electric charge “E” travels at high speed through a four-inch (ten-cm)-long cable toward the positive pole of a battery.
During this time, the electron reacts to an electric field (E), which keeps getting stronger and accelerates the electron with a force F = e x E. The amount of electric energy converted into kinetic energy of the electron is the product of the force and the distance over which the force was active; F multiplied by four inches (F x 10 cm).
FRICTION
Friction force is a less talked about force in physics. Rather than a fundamental concept, friction force is rather a collective term for processes where (technically usable) energy is converted into heat or lost in a different way.
Without friction, a car engine would only need to run at the start, electricity could be stored forever, and spaceships would not require a heat shield during re-entry into the atmosphere.